Wastewater reuse in agriculture requires...

EUROPEAN COMMISSIONEURO-MEDITERRANEAN PARTNERSHIP

Development of Tools and Guidelines for the Promotion of the Sustainable Urban

Wastewater Treatment and Reuse in the Agricultural Production in the Mediterranean

Countries

(MEDAWARE)Task 5: Technical Guidelines on Wastewater Utilisation

June 2005

TECHNICAL GUIDELINES ON WASTEWATER UTILISATION 1/171

MEDAWAREMEDAWARE ME8/AIDCO/2001/0515/59341-P033 ME8/AIDCO/2001/0515/59341-P033

Table of Contents

Table of Contents..................................................................................................1

List of Tables.........................................................................................................2

List of Figures........................................................................................................2

1. Introduction........................................................................................................2

1.1 Objectives and Content of this report..........................................................2

2. The Wastewater reuse and the regulatory status..............................................2

2.1 California-Wastewater Reuse Regulation...................................................2

2.2 U.S.EPA Water Reuse Guidelines..............................................................2

2.3 The WHO Guidelines..................................................................................2

2.4 Standards applied in various countries.......................................................22.4.1 Reuse standards in Cyprus.......................................................................................2

2.4.2 Reuse standards in France.......................................................................................2

2.4.3 Reuse standards in Italy............................................................................................2

2.4.4 Reuse standards in Israel.........................................................................................2

2.4.5 Reuse standards in Jordan.......................................................................................2

2.4.6 Reuse standards in Lebanon....................................................................................2

2.4.7 Reuse standards in Morocco.....................................................................................2

2.4.8 Reuse Standards in Palestine...................................................................................2

2.4.9 Reuse Standards in Spain........................................................................................2

2.4.10 Reuse Standards in Turkey.....................................................................................2

2.5 Comparison of reuse standards and standards for irrigation in various

countries............................................................................................................2

2.6 EU environmental legislation on water quality.............................................2

2.7 General conclusions and comparison.........................................................2

3. Pathogens and Public Health............................................................................2

3.1 Pathogenic Microoganisms.........................................................................23.1.1 Bacteria..................................................................................................................... 2

3.1.2 Viruses...................................................................................................................... 2

3.1.3 Protozoan.................................................................................................................. 2

3.1.4 Helminths.................................................................................................................. 2

3.2 Survival of Pathogens on Food Crops.........................................................2

3.3 Survival of pathogens on non- food crops...................................................2


3.4 Reduction of Pathogens through Wastewater Treatment...........................2

3.5 Removal of Parasites through Stabilization Ponds.....................................2

3.6 Removal of Parasites by secondary and tertiary treatment.........................23.6.1 Removal of Pathogens by Primary Sedimentation....................................................2

3.6.2 Filtration.................................................................................................................... 2

3.7 Advanced Wastewater treatment................................................................23.7.1 Reduction of Pathogens through Disinfection Processes..........................................2

3.7.2 Disinfection with chlorine...........................................................................................2

3.7.3 Disinfection with Ozone (O3).....................................................................................2

3.7.4 Disinfection with UV radiation....................................................................................2

4. Groups of population at risk and epidemiological evidence of human health

effects associated with wastewater irrigation........................................................2

4.1 Groups of population at risk........................................................................2

4.2 Human Health effects associated with wastewater irrigation......................2

4.3 Effects of use of untreated wastewater.......................................................24.3.1 Effects on farm workers or wastewater treatment plant workers...............................2

4.3.2 Effects on consumers of vegetable crops.................................................................2

4.4 Effects of use of treated wastewater...........................................................24.4.1 Effects on farm workers or nearby populations.........................................................2

4.4.2 Effects on consumers of vegetable crops.................................................................2

4.5 Exposure to raw wastewater.......................................................................2

4.6 Exposure to partially treated wastewater....................................................2

4.7 Risks to consumers related to unrestricted irrigation..................................2

4.8 Effects on farm workers or wastewater treatment plant workers.................2

4.9 Effects on consumers of vegetable crops...................................................2

4.10 Evidence from microbiological studies of crops irrigated with treated

wastewater........................................................................................................2

4.11 Studies on contamination of vegetable crops with nematode eggs...........2

4.12 Human Safety and Control........................................................................2

5. Crops.................................................................................................................2

5.1 Categorization of Crops..............................................................................2

5.2 Restrictions on types of crops irrigated with wastewater.............................2

5.3 Crop selection considerations and criteria..................................................2


5.3.1 Effects of salinity on crops........................................................................................2

5.3.2 Toxicity hazards on crops.........................................................................................2

6. Irrigation Methods..............................................................................................2

6.1 Conventional Surface Irrigation methods....................................................2

6.2 Modern Irrigation methods..........................................................................26.2.1 Flood irrigation..........................................................................................................2

6.2.2 Furrow irrigation........................................................................................................2

6.2.3 Basin Irrigation..........................................................................................................2

6.2.4 Sprinkler.................................................................................................................... 2

6.2.5 Drip systems.............................................................................................................2

6.2.6 Bubbler Irrigation.......................................................................................................2

6.2.7 Advantages and disadvantages of different methods of wastewater irrigation..........2

6.3 Proplems with water quality in irrigation......................................................26.3.1 Salinity...................................................................................................................... 2

6.3.2 Specific Ion toxicity....................................................................................................2

6.3.3 Water infiltration rate.................................................................................................2

6.3.4 Other problems.........................................................................................................2

6.4 Steps to improve irrigation efficiency...........................................................2

6.5 Suitability of irrigation methods...................................................................26.5.1 Natural conditions.....................................................................................................2

6.5.2 Type of crop..............................................................................................................2

6.5.3 Type of technology....................................................................................................2

6.5.4 Previous experience with irrigation............................................................................2

6.5.5 Required labour inputs..............................................................................................2

6.6 Selection between Basin, Furrow or Flood Irrigation...................................26.6.1 Land Characteristics.................................................................................................2

6.6.2 Type of crop..............................................................................................................2

6.6.3 Required depth of irrigation application.....................................................................2

6.6.4 Level of Technology..................................................................................................2

6.6.5 Previous experience with irrigation............................................................................2

6.6.6 Required labour inputs..............................................................................................2

7. Storage of water (reservoirs).............................................................................2

7.1 The need for storage...................................................................................2

7.2 Health impacts associated with storage reservoirs.....................................27.2.1 Loss of disinfectant residual......................................................................................2


7.2.2 Increase in pH...........................................................................................................2

7.2.3 Corrosion and occurrence of hydrogen sulphide.......................................................2

7.2.4 Iron and Manganese.................................................................................................2

7.3 Microbiological Problems............................................................................2

7.4 Physical problems.......................................................................................27.4.1 Sediment buildup......................................................................................................2

7.4.2 Contaminants............................................................................................................2

7.4.3 Temperature..............................................................................................................2

7.5 Open and enclosed reservoirs....................................................................27.5.1 Storage reservoirs open and closed..........................................................................2

7.5.2 Inlet/Outlet Designs...................................................................................................2

7.6 Problems with storage open reservoirs.......................................................2

7.7 Guidelines for avoiding problems in enclosed reservoirs............................2

7.8 Disinfection of tanks....................................................................................27.8.1 Reservoir maintenance and inspections...................................................................2

7.8.2 Other useful points in storage tanks..........................................................................2

References............................................................................................................2


List of Tables

Table 2-1: Representative uses, application methods for reclaimed water and

conditions in which use is allowed in California..................................2

Table 2-2: California water recycling criteriaa........................................................2

Table 2-3i: EPA Recommended Limits for Constituents in Reclaimed Water for

Irrigation..............................................................................................2

Table 2-3ii: EPA Suggested Guidelines for Water Reuse....................................2

Table 2-4: Guidelines for Unrestricted Urban Reuse of reclaimed water in states

of the US.............................................................................................2

Table 2-5: Guidelines for Restricted Urban Reuse of reclaimed water in states of

the US.................................................................................................2

Table 2-6: Guidelines for Agriculture Reuse; Food Crops of reclaimed water in

states of the US..................................................................................2

Table 2-7: Guidelines for Agriculture Reuse; Non-Food Crops of reclaimed water

in states of the US..............................................................................2

Table 2-8: Guidelines for the use of treated wastewater in agriculture a...............2

Table 2-9: Guidelines for the quality of reclaimed water used for irrigation in

Cyprus................................................................................................2

Table 2-10: Microbiological standards for irrigation with municipal wastewater:

comparison of regional guidelines with national and WHO standards 2

Table 2-11: Proposed maximum levels for dissolved and suspended elements

and compounds and for different parameters in effluents for

unrestricted irrigation and discharge to rivers.....................................2

Table 2-12: Allowable Limits for wastewater reuse and criteria for reuse in

irrigation..............................................................................................2

Table 2-13: Jordan Standard numbers 893 (JS #893) of the year 1995 for treated

wastewater disposal...........................................................................2

Table 2-14: Guidelines for Reuse in Irrigation.....................................................2

Table 2-15: Environmental limit values for wastewater discharged into seawater 2


Table 2-16: Environmental limit values for wastewater discharged into surface

waters.................................................................................................2

Table 2-17: Use of wastewater criteria in Morocco...............................................2

Table 2-18: Quality standards of water in order to be used for irrigation in

Morocco..............................................................................................2

Table 2-19: Draft microbiological quality guidelines and criteria for irrigation in

the proposed Spanish national regulation (1995)...............................2

Table 2-20: Turkish water quality criteria for irrigation, according to classes........2

Table 2-21: Classification of irrigation water with respect to resistance of plants

to boron mineral..................................................................................2

Table 2-22: Maximum allowable concentration of heavy metals and toxic

elements in irrigation, water in Turkey................................................2

Table 2-23: The technical limitations and related basis on reuse of water in

irrigation..............................................................................................2

Table 2-24: Suitability of treated domestic wastewater in irrigation without

disinfection..........................................................................................2

Table 2-25: Summary of Water Recycling Guidelines and Mandatory Standards

in the United States and Other Countries...........................................2

Table 2-26: Parameters given in Directive 98/83/EC............................................2

Table 2-27: Quality requirements for bathing water..............................................2

Table 2-28: Characteristics of surface water intended for the abstraction of

drinking water.....................................................................................2

Table 2-29: General conclusions and comparison between the available reuse

guidelines of WHO, recycling criteria of California, U.S.EPA and the

following Directives (76/160/EEC, 75/440/EEC, 98/83/EC)................2

Table 3-1: Epidemiological characteristics of enteric pathogens in terms of their

effectiveness in causing infections through wastewater irrigation.......2

Table 3-2: Microbial pathogens detected in untreated wastewaters.....................2

Table 3-3: Microorganism Concentrations in Raw Wastewater...........................2

Table 3-4: Microorganisms Concentrations in Secondary Non-Disinfected

Wastewater.........................................................................................2


Table 3-5: Survival of viral particles and bacteria in soil and groundwater...........2

Table 3-6: Typical Pathogen Survival Times at 20-300C.......................................2

Table 3-7: Levels of wastewater treatment...........................................................2

Table 3-8: Characteristics of an ideal disinfectant................................................2

Table 3-9: Comparison of different disinfection treatments...................................2

Table 3-10: Removal or destruction of bacteria by different treatment processes2

Table 3-11: Expected removal of excreted organisms in various wastewater

treatment processes. Values are expressed as log10 units 4 log10

units (i.e.equivalent to = 10-4 = 99.9 percent removal)........................2

Table 4-1: Summary of health risks associated with the use of wastewater in

irrigation..............................................................................................2

Table 4-2: Estimated risks from the use of untreated or treated wastewater in

irrigation of viral infection per person per year for various

concentrations of E. colia.....................................................................2

Table 5-1: Groups of cultivated plants..................................................................2

Table 5-2: Categorization of crops in relation to exposed group and health

control measure..................................................................................2

Table 5-3: Water requirements, sensitive to water supply and water utilization

efficiency of some selected crops.......................................................2

Table 5-4: Salt moderately tolerant agricultural crops...........................................2

Table 5-5: Salt moderately sensitive agricultural crops........................................2

Table 5-6: Salt sensitive agricultural crops...........................................................2

Table 5-7: Relative tolerance of selected crops to exchangeable sodium............2

Table 5-8: Chloride tolerance of some fruit crop cultivars and rootstocks............2

Table 5-9: Relative Boron tolerance of agricultural crops1....................................2

Table 5-10: Threshold levels of trace elements for crop production.....................2

Table 6-1: Conventional irrigation methods and suitable crops............................2

Table 6-2: Advantages and disadvantages of different methods of wastewater

irrigation in terms of disease transmission risks, water use efficiency,

and cost..............................................................................................2

Table 6-3: Basic features of some selected irrigation systems.............................2


Table 6-4: Evaluation of common irrigation methods in relation to the use of

treated wastewater.............................................................................2

Table 6-5: Tolerance of selected crops to total dissolved solids in irrigation water,

as determined by research in California, U.S.A..................................2

Table 6-6: Natural conditions and the choice of irrigation type.............................2

Table 6-7: Selection of an irrigation method based on the depth of the net

irrigation application............................................................................2

Table 7-1: Water quality problems associated with storage water facilities..........2

Table 7-2: Problems in the operation of open reservoirs used for the storage of

reclaimed water..................................................................................2

Table 7-3: Management strategies for open reservoirs used for the storage of

reclaimed water..................................................................................2

Table 7-4: Management strategies for enclosed reservoirs used for the storage

of reclaimed water..............................................................................2

Table 7- 5: Problems in the operation of enclosed reservoirs used for the storage

of reclaimed water..............................................................................2


List of Figures

Figure 1-1: The role of engineered treatment, reclamation, and reuse

facilities in the cycling of water through the hydrologic cycle 11

Figure 2-1: EU Water Quality Standards 57

Figure 3-1: Bacterium 66

Figure 3-2: Procaryotic cell 67

Figure 3-3: Virus 67

Figure 3-4: Protozoan 69

Figure 3-5: Helminths (Roundworm) 69

Figure 5-1: Treatments for agriculture wastewater use 111

Figure 6-1: Flood irrigation 123

Figure 6-2: Furrow irrigation 124

Figure 6-3: Basin irrigation 126

Figure 6-4: Sprinkler irrigation 128

Figure 6-5: Center Pivot 129

Figure 6-6: Travelling Gun 130

Figure 6-7: Drip irrigation 131

Figure 6-8: Bubbler irrigation 132


1. Introduction

Agricultural use of water resources nowadays is of great importance due to the

high volumes that are necessary. Irrigated agriculture will play a significant role in

the sustainability of crop production in years to come. However, in the future,

further reduction in the extent of exploitable water resources, together with

competing claims for water for municipal and industrial use, will significantly

reduce the availability of water for agriculture.

The term wastewater reuse is often used synonymously with the terms

wastewater recycling and wastewater reclamation. But they are three different

terms:

Wastewaterreclamation

Involves the treatment or processing of wastewater to make it

reusable (Asano, 1998).

Wastewaterreuse

Or water reuse is the beneficial use of treated water (Asano,

1998)

Wastewaterrecycling

Or water recycling is the use of wastewater that is captured and

redirect back into the same water use scheme (Metcalf and

Eddy, 2003)

The U.S. Environmental Protection Agency (EPA) defines wastewater reuse as,

«using wastewater or reclaimed water from one application for another

application» (EPA, 2004). The deliberate use of reclaimed water or wastewater

must be in compliance with applicable rules for a beneficial purpose (landscape

irrigation, agricultural irrigation, aesthetic uses, ground water recharge, industrial

uses, and fire protection). A common type of recycled water is water that has

been reclaimed from municipal wastewater (sewage). The most common

reasons for establishing a wastewater reuse program is to utilize new water

resources to satisfy the increasing water demands and to attain this target with

the lowest cost possible.


During the last two decades the use of wastewater for irrigation of crops has

been substantially increased (Mara and Cairncross, 1989) due to:

- The increasing scarcity of alternative water resources for irrigation.

- The high costs of fertilisers.

- The assurances that health risks and soil damage are minimal, if the

necessary precautions are taken.

- The high costs of advanced wastewater treatment plants needed for

discharging effluents to water bodies.

- The socio-cultural acceptance of the practice.

- The recognition by water resource planners of the value of the practice.

In Figure 1-1 a general representation of the water usage in nowadays is shown.

This important figure presents the cycling of water from surface and groundwater

resources to water treatment facilities, irrigation, municipal, and industrial

applications, and to water reclamation and reuse facilities. The major pathways

of water reuse include irrigation, industrial use, surface water replenishment, and

groundwater recharge.

Figure 1-1: The role of engineered treatment, reclamation, and reuse facilities in the cycling of

water through the hydrologic cycle (Asano and Levine, 1996).

Surface water replenishment and ground water recharge also occur through

natural drainage and through infiltration of irrigation and stormwater runoff. The


potencial use of reclaimed water for a potable water source is also shown. The

quantity of water that is transferred depends on the watershed characteristics,

climatic and geohydrologic factors, the degree of water utilization for various

purposes, and the degree of direct or indirect water reuse. The water used or

reused for agricultural and landscape irrigation includes agricultural, residential,

commercial, and municipal applications.

As it is already showed, water reuse applications consist of seven categories

described next. The relative amount of water used in each category varies locally

and regionally due to differences in specific water use requirements constraints.

1. Agricultural irrigation represents the largest current use of reclaimed water

throughout the world. This reuse category offers significant future opportunities

for water reuse in both industrialized countries and developing countries.It

separates to agricultural reuse on food crops ( not commercially processed and

commercially processed food crops and surface irrigation of orchards and

vineyards) and agricultural reuse on non- food crops (pasture for milking animals

and fodder, fiber and seed crops).

2. Landscape irrigation is the second largest user of reclaimed water in

industrialized countries and it includes the irrigation of parks; playgrounds; golf

courses; freeway medians; landscaped areas around commercial, office, and

industrial developments; and landscaped areas around residences. Many

landscape irrigation projects involve dual distribution systems, which consist of

one distribution network for potable water and a separate pipeline to transport

reclaimed water.

3. Industrial activities represent the third major use of reclaimed water,

primarily for cooling and process needs. Cooling water creates the single largest

industrial demand for water and as such is the predominant industrial water

reuse either for cooling towers or cooling ponds. Industrial uses vary greatly and


water quality requirements tend to be industry-specific. To provide adequate

water quality, supplemental treatment may be required beyond conventional

secondary wastewater treatment.

4. Groundwater recharge is the fourth largest application for water reuse, either

via spreading basins or direct injection to groundwater aquifers. Groundwater

recharge includes groundwater replenishment by assimilation and storage of

reclaimed water in groundwater aquifers, or establishing hydraulic barriers

against salt-water intrusion in coastal areas.

5. Recreational and environmental uses constitute the fifth largest use of

reclaimed water in industrialized countries and involve non-potable uses related

to land-based water features such as the development of recreational lakes,

marsh enhancement, and stream flow augmentation. Reclaimed water

impoundments can be incorporated into urban landscape developments. Man-

made lakes, golf course storage ponds and water traps can be supplied with

reclaimed water. Reclaimed water has been applied to wetlands for a variety of

reasons including: habitat creation, restoration and/or enhancement, provision for

additional treatment prior to discharge to receiving water, and provision for a wet

weather disposal alternative for reclaimed water.

6. Non-potable urban uses include fire protection, air conditioning, toilet

flushing, construction water, and flushing of sanitary sewers. Typically, for

economic reasons, these uses are incidental and depend on the proximity of the

wastewater reclamation plant to the point of use. In addition, the economic

advantages of urban uses can be enhanced by coupling with other ongoing

reuse applications such as landscape irrigation.

7. Potable reuse is another water reuse opportunity, which could occur either by

blending in water supply storage reservoirs or, in the extreme, by direct input of

highly treated wastewater into the water distribution system.


1.1 Objectives and Content of this report

The objective of this study is to demonstrate that urban wastewater management

can and must be transformed from a disposal-based linear system to a recovery

based closed loop system that promotes the conservation of water and natural

resources while at the same time safeguarding public health and environment.

An attempt is been made to:

Present the quality standards that exists for wastewater reuse and make a

comparison between them

Present pathogens and their impact to human health and how wastewater

treatment reduce their existence

Specify the groups of population at risk and which is the effect from

wastewater irrigation to human health

Review the irrigation methods and develop specifications for storage

reservoirs


2. The Wastewater reuse and the regulatory status

There is not a common regulation of wastewater reuse in the world due to

various climatic, geological and geographical conditions, water resources, type of

crops and soils, economic and social aspects, and country /state policies towards

using wastewater influents for irrigation purposes. Some countries and

organizations have already established reuse standards such as USEPA,

California, WHO, FAO, Israel, France, Italy (EPA, 2004). Most of the developing

countries have adopted their own standards from the leading standards set by

either FAO, WHO, California, etc. There is not any common regulation of

wastewater reuse also at European level.

Most countries where wastewater irrigation is practiced have public health

regulations to protect both the agricultural workers and the irrigated crops

consumers. The regulations may also prohibit such irrigation within specified

periods.

In most industrialized countries, these precautions can usually be met without

major difficulties because of water pollution control requirements for treatment.

Regulations in the industrialized countries reflect their own sanitary conditions.

In developing countries, the technological equipment necessary to produce

effluent of a mandated quality is often unavailable or, if available, not maintained.

The regulatory agencies, if they exist, can seldom enforce the standards.

Irrigation with wastewater is therefore often uncontrolled in these countries, and

both the agricultural workers and the consumers are at risk.

Recent epidemiological studies of untreated wastewater reuse concluded that the

danger of infection was (Khouri, 1994):

1. high with intestinal nematodes;

2. moderate with bacterial infections and diarrheas;

3. minimal with viral infections and diarrheas, and hepatitis A; and


4. High to nonexistent with trematode and cestode infections, schistosomiasis,

clonorchiasis, and taeniasis, depending on local practices and circumstances.

The best way to overcome the legal problems of unenforceable standards in the

developing countries is to set realistic criteria reflecting prevalent disease risks.

This tangible aim would result in fewer risks to health and enforceable standards

that will encourage the safe use of wastewater for irrigation.

2.1 California-Wastewater Reuse Regulation

The fist regulation on wastewater reuse for irrigation was developed in 1918

(Asano and Levine, 1996) and it is considered as the most comprehensive one in

regards to public health. After that, regulations have been developed for

wastewater treatment such as for sludge, ponds, chemical treatment, filtration,

disinfection, nutrient removal. Since 1960, California has promoted wastewater

reuse by drafting regulations and promoting research for: irrigation, industrial and

municipal reuse, groundwater recharge, potable reuse. Today these reuse

schemes have being developed in many contexts beyond California worldwide.

In 2000 the State of California revised the Water Recycling Criteria (Title 22

requlations) which are summarised in Table 2-2 (State of California, 2000). The

representative uses and application methods are listed in Table 2-1.

Table 2-1: Representative uses, application methods for reclaimed water and conditions in which use is allowed in California

General useDisinfected

tertiary reclaimed

water

Disinfected secondary-22

reclaimed water


reclaimed water

Undisinfected secondary reclaimed

waterAll water uses other than potable use or food preparationb and other than groundwater recharge (governed by other regulations)

Allowedb Not allowed Not allowed Not allowed

Irrigation of:Parks, playgrounds, school yards, residencial yards, and golf courses associated with residences

Spray, drip, or surface

Not allowed Not allowed Not allowed

Restricted-access golf courses, cemeteries, freeway landscapes




Not allowed

Nonedible vegetation at other areas with limited public exposurec




Not allowed


Sod farms Spray, drip, or surface



Not allowed

Ornamental plants for commercial use Spray, drip, or surface



Not allowed

All food crops Spray, drip, or surface

Not allowed Not allowed Not allowed

Food crops that are above ground and not contacted by reclaimed water


Drip, or surface Not allowed Not allowed

Fodder (alfalfa), fiber (cotton), and seed crops not eaten by humans




Drip, or surface

Orchards and vineyards bearing food crops


Drip, or surface Drip, or surface

Drip, or surface

Orchards and vineyards not bearing food crops during irrigation




Drip,or surface

Christmas trees and other trees not bearing food crops




Drip, or surface

Food crops which must undergo commercial pathogen-destroying processing before consumption (e.g., sugar beets)




Drip, or surface

a From California Code Regulations,Title 22, Division 4, Chapter 3 Water Recycling Criteria, Sections 60301 et seq., Dec. 2000b Disinfected tertiary effluent is suitable for all water uses that are not for potable use or food preparation, do

not involve incorporation of reclaimed water into drink or food for humans, and do not conflict with provisions of the California Code of Regulations, federal regulations, statute, or other law.

c Disinfected secondary-2.2 reclaimed water and disinfected secondary -23 reclaimed water are suitable for irrigation of landscape vegetation and nonedible plants where(a) the public would have access and exposure to irrigation water similar to that which would occur at a golf course or cemetery, and (b) children do not have direct access and exposure to irrigation water. There is no concern regarding access and exposure when disinfected tertiary reclaimed water is used.

Table 2-2: California water recycling criteriaa

Category of reclaimed water

Total coliformMPN/100ml

Turbidity,NTU

Suitable uses

Disinfected tertiaryb

<2.2 2 average5 maximum

All uses shown in § 1

Disinfected secondary-2.2

<2.2 nae All uses shown in table except irrigation of parks and playgrounds,c food crops coming in contact with reclaimed water, nonrestricted impoundments


<23 nae Same restrictions as disinfected secondary-2.2, except no food crop irrigation, no nonrestricted impoundment, and no watering of yards

Undisinfected secondaryd

nae nae Drip or surface irrigation of fodder, fiber, seed orchard, and tree crops and sugar beets (commercially processed food crops)

aFrom California Code Regulations, Title 22, Division 4, Chapter 3 Water Recycling Criteria, Sections 60301 et seq., Dec.2, 2000.bFiltered through natural undisturbed soils or filter media,such as sand or diatomaceous earth.cUrban areas such as parks, playgrounds, school yards, residencial yards, and golf courses associated with residences.dUndisinfected wastewater means wastewater in which the organic matter has been stabilized, is nonputrescible,and contains dissolved oxygen.ena= not applicable.


2.2 U.S.EPA Water Reuse Guidelines

In 1992, EPA developed the Guidelines for Water Reuse, a comprehensive,

technical document. Some of the information contained in this document includes

a summary of state reuse requirements, guidelines for treating and reusing

water, key issues in evaluating wastewater reuse opportunities, and case studies

illustrating legal issues, such as water rights, that affect wastewater reuse. The

guidelines also include recommended treatment processes, reclaimed water

quality limits, monitoring frequencies, setback distances, and other controls for

various water reuse applications. The guidelines were updated in 2004. The

tables that follow (Tables 2-3i and 2-3ii), summarise the USEPA suggested

guidelines for water reuse according to type of use.

Both reclaimed water quality limits and wastewater treatment unit processes are

recommended because (1) combination of treatment and quality requirements

known to produce reclaimed water of acceptable quality obviate the need to

monitor the finished water for certain constituents; (2) it is considered expensive,

time consuming, and thus in some cases, monitoring for pathogenic

microorganisms is eliminated without compromising health protection and; (3)

treatment reliability is enhanced. The guidelines use faecal coliform organisms as

indicators of pollution and not parasite or virus limits for the following reasons:

Concentration of parasites and viruses is much lower.

The type and concentration of viruses in wastewater are difficult to be

determined accurately because of low virus recovery rates.

There is a limited number of facilities having the personnel and equipment

necessary to perform the analyses.

The laboratory analyses can take as long as 4 weeks to complete.

There have not been any documented cases of viral disease resulting from

the reuse of wastewater in the U.S.

Parasites presence in industrialiazed countries is limited.

Table 2-3i: EPA Recommended Limits for Constituents in Reclaimed Water for Irrigation


Source: EPA, Guidelines for Water Reuse, September 2004, EPA/625/R-04/108; Table 2-7, page 25.


Table 2-3ii: EPA Suggested Guidelines for Water Reuse


1. Unless otherwise noted, recommended quality limits apply to the reclaimed water at the point of discharge from the treatment facility.2. Setback distances are recommended to protect potable water supply sources from contamination and to protect humans from unreasonable health risks due to exposure to

reclaimed water.3. Secondary treatment processes include activated sludge processes, trickling filters, rotating biological contactors, and many stabilization pond systems. Secondary treatment

should produce effluent in which both the BOD and SS do not exceed 30 mg/l.4. Filtration means the passing of wastewater through natural undisturbed soils or filter media such as sand and/or anthracite.5. Disinfection means the destruction, inactivation, or removal of pathogenic microorganisms by chemical, physical, or biological means. Disinfection may be accomplished by

chlorination, ozonation, other chemical disinfectants, UV radiation, membrane processes, or other processes.6. As determined from the 5 day BOD test.7. The recommended turbidity limit should be met prior to disinfection. The average turbidity should be based on a 24 hour time period. The turbidity should not exceed 5 NTU at

any time. If SS is used in lieu of turbidity, the average SS should not exceed 5 mg/l.8. Unless otherwise noted, recommended coliform limits are median values determined from the bacteriological results of the last 7 days for which analyses have been completed.

Either the membrane filter or fermentation tube technique may be used.9. The number of fecal coliform organisms should not exceed 14 100 ml in any sample.10. Total chlorine residual after a minimum contact time for 30 minutes.11. The number of fecal coliform organisms should not exceed 800/100 ml in any sample.12. Some stabilization pond systems may be able to meet this coliform limit without disinfection.13. It is advisable to fully characterize the microbiological quality of the reclaimed water prior to implementation of a reuse program.14. Commercially processed food crops are those that, prior to sale to the public or others, have undergone chemical or physical processing sufficient to destroy pathogens.15. Advanced wastewater treatment processes include chemical clarification, carbon adsorption, reverse osmosis and other membrane processes, air stripping, ultrafiltration, and ion

exchange.16. Monitoring should include inorganic and organic compounds, or classes of compounds, that are known or suspected to be toxic, carcinogenic, teratogenic, or mutagenic and are

not included in the drinking water standards.

Source: EPA, Guidelines for Water Reuse, September 2004, EPA/625/R-04/108; Table 4-13, pages 167-170.


According to the EPA Guidelines for Water Reuse of 2004, the major reuse

categories are, urban, industrial, agricultural, environmental and recreational,

groundwater recharge and augmentation of potable supplies. Quantity and

quality requirements are considered for each reuse application. However,

regulations and guidelines in U.S.A vary from state to state. States such as

Arizona, California, Florida, Hawaii, Nevada, Texas and Washington have

developed regulations or guidelines which provide successful reuse programmes

and long–term experience. The tables that follow (Tables 2-4 to 2-7), list the

standards set by these states.

Unrestricted urban reuse involves the use of reclaimed water where public

exposure is likely in the reuse application, thereby necessitating a high degree of

treatment. States specifying a treatment process generally require a minimum of

secondary treatment and treatment with disinfection. The majority though of

states require additional levels of treatment (e.g. oxidation, coagulation, and

filtration). Table 2-4 gives the guidelines according to some states for unrestricted

urban reuse. Where specified, limits on BOD range from 5 mg/l to 30 mg/l.

Average fecal and total coliform limits range from non-detectable to 20/100 ml.

Higher single sample fecal and total coliform limits are allowed in several state

regulations. Florida on the other hand requires that 75 percent of the fecal

coliform samples taken over a 30-day period be below detectable levels, with no

single sample in excess of 25/100 ml, while Texas requires that no single fecal

coliform count exceed 75/100 ml.

So far, no states have set limits on certain pathogenic organisms for unrestricted

urban reuse, except Florida that requires monitoring of Giardia and

Cryptosporidium with sampling frequency based on treatment plant capacity: for

less than 1 mgd (44 l/s), sampling is required one time during each 5-year period;

for equal to or greater than 1 mgd (44 l/ s), sampling is required one time during

each 2-year period. Samples are to be taken after the stage of disinfection.


Table 2-4: Guidelines for Unrestricted Urban Reuse of reclaimed water in states of the US


Table 2-5 presents the Restricted Urban Reuse requirements. One way of

defining this concept is by saying that it involves the use of reclaimed water

where public exposure to the reclaimed water is controlled, and for that reason

the treatment requirements may not be as strict as in Table 2-4. Most states of

the U.S. do not specify limit values for BOD in contrast with the US EPA which

specifies BOD and SS (see Table 2-3ii).

The use of reclaimed water for irrigation of food crops is prohibited in some

states, while others allow irrigation of food crops with reclaimed water only if the

crop is going to be processed and not eaten raw. Nevada allows only surface

irrigation of fruit or nut bearing trees. Treatment requirements range from

secondary treatment (Nevada) for irrigation of processed food crops, to oxidation,

coagulation, filtration, and disinfection (Arizona, California, Florida, Hawaii, and

Washington). Table 2-6 shows the reclaimed water quality and treatment

requirements for irrigation of food crops.

Table 2-5: Guidelines for Restricted Urban Reuse of reclaimed water in states of the US



Table 2-6: Guidelines for Agriculture Reuse; Food Crops of reclaimed water in states of the US


The use of reclaimed water for agricultural irrigation of non-food crops

corresponds to reduced prospect of human exposure to the water, which results

to less stringent treatment and water quality requirements than other forms of

reuse. In most of the states, secondary treatment followed by disinfection is


required, although Hawaii also requires filtration. Table 2-7 shows the reclaimed

water quality and treatment requirements for irrigation of non-food crops.

Table 2-7: Guidelines for Agriculture Reuse; Non-Food Crops of reclaimed water in states of the

US


2.3 The WHO Guidelines

Other important guidelines that exist for wastewater reuse are the ones published

by the World Health Organization (WHO), and are mainly focused on the needs

of developing countries. WHO guidelines specify the microbiological quality and

the treatment method required to achieve this quality, which is limited to the use

of stabilisation ponds since it is cheaper, simpler and ensure removal of parasites

which is the most infectious agent in the developing world. WHO guidelines are

presented in Table 2-8.

To understand better this table, let’s elaborate on Category A. The WHO has

recommended that irrigation of crops likely to be eaten uncooked, sports fields,

and public parks should be irrigated with wastewater treated by a series of

stabilization ponds. The ponds are designed to achieve a microbiological quality


of less than or equal to 1 intestinal nematode per liter and faecal coliforms less

than or equal to 1000 per 100ml.

The main features of the WHO (1989) guidelines for wastewater reuse in

agriculture are therefore as follows:

Wastewater is considered as a resource to be used, but used safely.

The aim of the guidelines is to protect exposed populations (consumers, farm

workers, populations living near irrigated fields) against excess infection.

Faecal coliforms and intestinal nematode eggs are used as pathogen

indicators.

Nematodes are included in the guidelines since infectious diseases in

developing countries are mainly due to the presence of parasites which are

more resistant to treatment.

Measures comprising good reuse management practice are proposed

alongside wastewater quality and treatment goals; restrictions on crops to be

irrigated with wastewater; selection of irrigation methods providing increased

health protection, and observation of good personal hygiene (including the

use of protective clothing).

Table 2-8: Guidelines for the use of treated wastewater in agriculture a

Category Reuse conditions Exposed group

Intestinal nematodeb

(arithmetic mean no. eggs per litre)c

Faecal coliforms (geometric mean no. per 100ml)c

Wastewater treatment expected to achieve the required microbiological guideline

Α Irrigation of crops likely to be eaten uncooked, sports fields, public parksd

Workers, consumers, public

≤1 ≤1000 A series of stabilization ponds designed to achieve the microbiological quality indicated, or equivalent treatment

Β Irrigation of cereal crops, industrial crops, fodder crops, pasture and treese

Workers ≤1 No standard recommended

Retention in stabilization ponds for 8-10 days or equivalent helminth and faecal coliform removal

C Localized irrigation of crops in category B if exposure to workers and the public does not occur

None Not applicable

Not applicable

Pretreatment as required by irrigation technology, but not less than primary sedimentation

a In specific cases, local epidemiological, sociocultural and environmental factors should be taken into account and the guidelines modified accordingly.

b Ascaris and Trichuris species and hookworms.c During the irrigation period.


d A more stringent guideline (200 faecal coliforms per 100 ml) is appropriate for public lawns, such as hotel lawns, with which the public may cone into direct contact.

e In the case of fruit trees, irrigation should cease two weeks before fruit is picket, and no fruit should be picked off the ground. Sprinkler irrigation should be used.

Source: WHO, 1989

2.4 Standards applied in various countries

2.4.1 Reuse standards in Cyprus

Reuse guidelines in Cyprus have been established since 1990. In Cyprus fresh

water is presently used for the watering of football fields, parks, hotel gardens,

road islands, forests as well as irrigation of permanent crops. Some reclaimed

water covers partly the needs in agriculture. Already some quantities are used for

the following crops: citrus, olives, vines, fodders and landscape. Direct use of

treated wastewater is used for irrigation. The guidelines for irrigation are

standards for Biological Oxygen Demand (BOD) and suspended solids. For crops

the guidelines are: BOD and suspended solids 10mg/l, faecal coli 5 with a

maximum of 15, and the treatment scenario is secondary, tertiary and disinfection

with chlorine. Storage of a period of 7 days before the use is required. This

period is needed for the destruction of pathogens through the sun and for the

worms to settle down.

Besides these strict guidelines, there are practical guidelines about the marking

of the transport system and tap points and irrigation methods. A micro-toxicity

test has been developed for testing the effluent on pollutions. If the effluent

contains toxic components then the source will be excluded for further reuse. For

irrigation water nutrients are desirable. In Cyprus phosphorus is not removed in

waste water treatment plant (WWTP), because it is a nutrient for the crops.

During the storage an additional treatment takes place and the water is more

bacterial safe.

Water resources in Cyprus are limited and, with the rapid development of urban

and rural domestic supplies, conventional water resources have been seriously

depleted. As a result, the reclamation and use of wastewater has become a


realistic option for providing reliable sources of water to meet shortages and to

cover water needs, as well as for meeting wastewater disposal regulations aimed

at protecting the environment and public health. However, the use of wastewater

could itself be associated with severe environmental and health impacts.

Recently, priority has been given to research on animal feeding and human

health aspects. The results indicate that with the treatment level required in

Cyprus, with the irrigation technology available and with the code of practice

suggested, the health and environmental risks fall within acceptable levels

(Jenkins et al., 1994).

Table 2-9: Guidelines for the quality of reclaimed water used for irrigation in Cyprus

No. Allowed to be irrigated BOD5

(mg/l)SS(mg/l)

E. Coli/ 100ml

Eggs of intestinal worms / L*** Treatment required

1 All crops (a) A 10* 10* 5*15** Nil

Secondary and Tertiary and disinfection

2 Amenity areas of unlimited access and vegetables eaten cooked (b)

A 10*15*

10*15**

50*100**

Nil

Secondary and Tertiary and disinfection

3 Crops for humanconsumption.Amenity areas oflimited access.

A 20*30**

30*45**

200*1000**

Nil

Secondary disinfection and storage >7 daysor Tertiary and disinfection.

4 Fodder crops A 20*30**

30*45**

1000*5000**

Nil

Secondary and storage>7 days or tertiary anddisinfection.

B - - 1000*5000**

Stabilization - maturation ponds total retention time >60 days

5 Industrial crops A 50*70**

- 3000*10000** -

Secondary and Disinfection.

B - - 300*10000** -

Stabilization - maturation ponds total retention time >60 days

A Mechanised methods of treatment (activated sludge e.t.c.)B Stabilization Ponds* These values must not be exceeded in 80% of samples per month. Min. No. samples 5.** Maximum value allowed(a) Irrigation of leaved vegetables, bulbs and corms eaten uncooked is not allowed(b) Potatoes, beet-roots, colocasia.


In Cyprus, in order to control the treatment and use of wastewater and thereafter

to safeguard the environment and public health, very strict guidelines have been

formed relating to the quality and the use of treated wastewater (Table 2-9)

(Papadopoulos, 1995). These guidelines are stricter than those proposed by the

World Health Organization (WHO). In addition, the guidelines are followed by a

code of practice intended to ensure protection of public health and the

environment even further and they should be considered to be part of the

guidelines. In Table 2-9 the guidelines for the quality of wastewater used for

irrigation in Cyprus.

2.4.1.1 Code of practice for treated domestic sewage effluent used for irrigation in Cyprus1. The sewage treatment and disinfection must be kept and maintained

continuously in satisfactory and effective operation so long as treated sewage

effluent are intended for irrigation, and according to the license issued under

the existing legislation.

2. Skilled operators should be employed to attend the treatment and

disinfection plant, following formal approval by the appropriate authority that

the persons are competent to perform the required duties, necessary to

ensure that conditions of (1) are satisfied.

3. The treatment and disinfection plant must be attended every day

according to the program issued by the Authority and records to be kept of all

operations performed according to the instructions of the appropriate

Authority. A copy must be kept for easy access within the treatment facilities.

4. All outlets, taps and valves in the irrigation system must be secured to

prevent their use by unauthorized persons. All such outlets must be colored

red and clearly labelled so as to warn the public that the water is unsafe for

drinking.

5. No cross connections with any pipeline or works conveying potable water,

is allowed. All pipelines conveying sewage effluent must be satisfactorily

marked with red tape so as to distinguish them from domestic water supply. In

unavoidable cases where sewage/effluent and domestic water supply


pipelines must be laid close to each other the sewage or effluent pipes should

be buried at least 0.5 m below the domestic water pipes.

6. Irrigation methods allowed and conditions of application differ between

different plantations as follows:

a. Park lawns and ornamental in amenity areas of unlimited access:

Subsurface irrigation methods

Drip irrigation

Pop-up, low pressure and high precipitation rate, low angle

sprinklers (less than 11 degrees). Sprinkling preferably to be practiced

at night and when people are not around.

b. Park lawns and ornamental in amenity areas of limited access, industrial

and fodder crops:

Subsurface irrigation

Bubblers

Drip irrigation

Pop-up Sprinklers

Surface irrigation methods

Low capacity sprinklers

Spray or sprinkler irrigation, is allowed with a buffer zone of about 300

meters.

For fodder crops, irrigation is recommended to stop at least one week

before harvesting and no milking animals should be allowed to graze on

pastures irrigated with sewage. Vetenary Services should be informed.

c. Vines:

Drip irrigation

Minisprinklers and sprinklers (in case where crops get wetted, irrigation

should stop two weeks before harvesting).

Movable irrigation systems are not allowed.

No crops should be selected from the ground.

d. Fruit trees

Drip irrigation

Hose basin irrigation


Bubblers irrigation

Mini sprinklers

No fruits to be collected form the ground except for nut-trees. In case

where crops get wetted irrigation should stop one week before harvesting.

e. Vegetables


Drip irrigation

Crops must not come in contact with the ground or the effluents (only

vegetables which are supported). Other irrigation methods could also be

considered.

f. Vegetables eaten cooked.

Sprinklers


Drip irrigation

Other irrigation methods may be allowed after the approval of the

appropriate Authority Restrictions may be posed to any method of

irrigation by the appropriate authority in order to protect public health or

environment.

7. The following tertiary treatment methods are acceptable:

a. Coagulation plus flocculation followed by Rapid Sand Filtration.

b. Slow Sand Filters.

c. Any other method, which may secure the total removal of helminth ova

and reduce faecal coliforms to acceptable level. Must be approved by the

appropriate Authority.

8. Appropriate disinfection methods should be applied when sewage effluent

are to be used for irrigation. In the case of chlorination the total level of free

chlorine in the effluent at the outlet of the chlorination tank, after an hour of

contact time should be at least 0.5 mg/L and not greater than 2 mg/l.

9. Suitable facilities for monitoring of the essential quality parameters, should

be kept on site of treatment.

2.4.2 Reuse standards in France


France has been irrigating crops with wastewater for years. Because of a new

interest for wastewater reuse, the Health Authorities issued in 1991 the Health

guidelines for reuse, after treatment, of wastewater for crop and green spaces

irrigation (CSHPF, 1991).

In 1991 France enacted a comprehensive national code of practice under the

form of recommendations from the Conseil Supérieur díHygiène Publique de

France (CSHPF) (CSHPF, 1991). These recommendations use the WHO

guidelines as a basis, but complement them with strict rules of application. In

general, the approach is very cautious and the main restrictions given by the

CSHPF are:

The protection of the ground and surface water resources.

The restriction of uses according to the quality of the treated effluents.

The piping networks for the treated wastewaters.

The chemical quality of the treated effluents

The control of the sanitary rules applicable to wastewater treatment and

irrigation facilities

The training of operators and supervisors.

The CSHPF calls for strict observation of these restrictions to ensure the best

possible protection of the public health of the populations concerned (Bontoux,

2000). In fact, the authorizations for wastewater reuse are granted on a case by

case basis after review of a highly detailed dossier.

2.4.3 Reuse standards in Italy

Existing Italian legislation (Angelakis et al. 2003) General Technical Standards –

G.U. 21.2.77 sets the limits depending on the type of vegetables and grazing

crops to 2 and 20 FC/100 cm3, respectively. Moreover, the law prescribes that in

the presence of surface aquifers in direct contact with surface waters, adequate

preventive measures must be used to avoid any deterioration of their quality. A

new law relative to municipal wastewater is being prepared that gives better

attention to the management of water resources and in particular to the reuse of


treated wastewater. Industry will be encouraged to use treated wastewater.

Municipal wastewater treatment companies have already planned to build a

separate supply network for wastewater reuse by industries. In the metropolitan

area of Turin, for example, the two main companies (Azienda Po Sangone (APS)

and CIDIU) have already done so. Finally, a proposal for establishing national

regulations on wastewater recycling and reuse has been implemented. Criteria

proposed are incorporated in the recent legislation (No 258/2000) (Table 2-10),

(Angelakis et al., 2003).

Table 2-10: Microbiological standards for irrigation with municipal wastewater: comparison of regional guidelines with national and WHO standards

Organisation or region

TC (MPN/100 ml) (a) FC (MPN/100 ml) Nematode eggs (no/L)

WHO Not set 1,000(b) 1

Italy 2(b) , 20(c) Not set Not set

a mean value of 7 consecutive sampling daysb unrestricted irrigationc restricted irrigation

Source: Angelakis et al. 2003

2.4.4 Reuse standards in Israel

Israel has put wastewater reuse high on its list of national priorities. This is due to

a combination of severe water shortage, threat of pollution to its diminishing

water resources and a concentrated urban population with high levels of water

consumption and wastewater production. Indeed, relative to its size and means.

Israel has devoted more effort to wastewater reuse than any other country. This

has been reflected by the highest percentage in the world of wastewater effluents

reused for agricultural irrigation and wastewater reuse per capita, and the second

place in overall wastewater reuse (after California). Extensive experience has

been gathered in this field, and a multitude of technologies and approaches are

continuously being practiced and tested.

In Israel, shear necessity has dictated the construction and operation of large-

scale wastewater reuse schemes, mainly those which direct reclaimed


wastewater for reuse in agricultural irrigation. The Ministry of the Environment

has finalized recommendations for effluent quality standards for different

purposes. The recommended values, designed to minimize potential damage to

water sources, flora and soil, call for much higher treatment levels in existing and

future wastewater treatment plants. An agreement in principle has been reached

on the new effluent quality standards, and a techno-economic review of the

standard has been conducted. The objective is to treat 100% of the country’s

wastewater to a level enabling unrestricted irrigation in accordance with soil

sensitivity and without risk to soil and water sources. The proposed maximum

levels of dissolved and suspended elements and compounds and for different

parameters in effluents for unrestricted irrigation and discharge to rivers, are

shown in Table 2-11.

2.4.5 Reuse standards in Jordan

Jordan started to put regulations on wastewater reuse back in 1982. The first

regulation issued was very restricted and prevented the reuse of the effluent for

agriculture. A more liberal and less restricted law was issued in 1988 which

allowed the reuse of the treated wastewater for irrigating forestry and non edible

agricultural crops.

The first Jordanian standard for wastewater reuse was issued by the Ministry of

Water and Irrigation in 1995 which was given the number of 893 in 1995 (JS 893,

1995). The latest (third) version of the standards was given the number of 893

(JS 893, 2002). In 2003, the standards were revised and updated for various

qualities of water resources.

Table 2-11: Proposed maximum levels for dissolved and suspended elements and compounds and for different parameters in effluents for unrestricted irrigation and discharge to rivers Parameter Units Unrestricted Irrigation* Rivers


Electric Conductivity dS/m 1.4BOD mg/l 10 10TSS mg/l 10 10COD mg/l 100 70Ammonia mg/l 20 1.5Total nitrogen mg/l 20 10Total phosphorus mg/l 5 0.2Chloride mg/l 250 400Fluoride mg/l 2Sodium mg/l 150 200Faecal coliforms Unit per 100 ml 10 200Dissolved oxygen mg/l <0.5 <3pH mg/l 6.5-8.5 7.0-8.5Hydrocarbons mg/l 1Residual chlorine mg/l 1 0.05Anionic detergent mg/l 2 0.5Total oil mg/l 1SAR (mmol/L)0.5 5Boron mg/l 0.4Arsenic mg/l 0.1 0.1Barium mg/l 50Mercury mg/l 0.002 0.0005Chromium mg/l 0.1 0.05Nickel mg/l 0.2 0.05Selenium mg/l 0.02Lead mg/l 0.1 0.008Cadmium mg/l 0.01 0.005Zinc mg/l 2 0.2Iron mg/l 2Copper mg/l 0.2 0.02Manganese mg/l 0.2Aluminum mg/l 5Molybdenum mg/l 0.01Vanadium mg/l 0.1Beryllium mg/l 0.1Cobalt mg/l 0.05Lithium mg/l 2.5Cyanide mg/l 0.1 0.005*From soil, flora, hydrological and public health considerations Source: Israel Ministry of Environment, 2003

Table 2-12: Allowable Limits for wastewater reuse and criteria for reuse in irrigation Parameter Unit A1 B2 C3

Biological Oxygen Demand mg/l 30 200 300


Chemical Oxygen Demand mg/l 100 500 500Dissolved Oxygen mg/l >2 - -Total suspended solids mg/l 50 150 150pH Unit 6-9 6-9 6-9Turbidity NTU 10 - -Nitrate mg/l 30 45 45Total Nitrogen mg/l 45 70 70Escherishia Coli Most probable number or

colony forming unit/100 ml100 1000 -

Intestinal Helminthes Eggs Egg/l < or = 1 < or = 1 < or = 11 A Cooked Vegetables, Parks, Playgrounds and Sides of Roads within city limits, 2 B Fruit Trees, Sides of Roads outside city limits, and landscape3 C Field Crops, Industrial Crops and Forest Trees

Source: Medaware, 2005a

Table 2-13 presents the standards of 1995. In the latest standard JS 893, 2002

reclaimed water reuse for irrigation purposes consists of two main groups:

standards group and guidelines group.

It is prohibited to use reclaimed water for irrigating vegetables that are eaten

uncooked (raw). It is prohibited to use sprinkler irrigation except for irrigating golf

courses and in that case irrigation should practiced at night and the sprinklers

must be of the movable type and not accessible for day use. When using

reclaimed water for irrigating fruit trees, irrigation must be stopped two weeks

prior to fruits harvesting and any falling fruits in contact with the soil must be

removed.

Table 2-13: Jordan Standard numbers 893 (JS #893) of the year 1995 for treated wastewater disposal

Quality Cooked Fruit and Flow to Ground Aqua Park Fodder


Parameter, mg/L Except asotherwise indicated

Vegetables Forest Trees and Industrial

and Cereal Crops

Wadis and

Water Bodies

Water Recharge

Culture Crops

BOD <150 <150 <50 <50 ……… <50 <250COD <500 <500 <200 <200 ……… <200 <700DO >2 >2 >2 >2 >5 >2 >1TDS <2000 <2000 <2000 <1500 <2000 <2000 <2000TSS <200 <200 <50 <50 <25 <50 <250PH 6.0-9.0 6.0-9.0 6.0-9.0 6.0-9.0 6.5-9.0 6.0-9.0 6.0-9.0COLOR (UNIT) ……… ……… <75 <75 ……… <75 ………FOG <8 <8 <8 ABSENT <12 <8 <12PHENOL <0.002 <0.002 <0.002 <0.002 <0.001 <0.002 <0.002NO3-N <50 <50 <25 <25 ……… <25 <50NH4-N ……… ……… <15 <15 0.02 - 0.5 <50 ………TOTL –N <100 <100 <50 <50 ……… <75 ………PO4 –P ……… ……… <15 <15 ……… <15 ………Cl <350 <350 <350 <350 ……… <350 <350SO4 <1000 <1000 <1000 <1000 ……… <1000 <1000CO3 <6 <6 <6 <6 ……… <6 <6HCO3 <520 <520 <520 <520 ……… <520 <520Na <230 <230 <230 <230 ……… <230 <230Mg <60 <60 <60 <60 ……… <60 <60Ca <400 <400 <400 <400 ……… <400 <400SAR <9 <9 <9 <9 ……… <12 <9Al <5 <5 <5 <1 ……… <5 <5As <1 <0.1 <0.05 <0.05 <0.05 <0.1 <0.1Be <0.1 <0.1 <0.1 <0.1 0.011-1.10 <0.1 <0.1Cu <0.2 <0.2 <0.2 <0.2 0.01-0.04 <0.2 <0,2F <1.0 <1.0 <1.0 <1.0 1.5 <1.0 <1,0Fe <5.0 <5.0 <2.0 <1.0 0.5 <5.0 <5Li <2.5 0.07-5.0 <1 <1 ………….. <3 <5Mn <0.2 <0.2 <0.2 <0.2 1 <0.2 <0,2Ni <0.2 <0.2 <0.2 <0.2 0.05-0.4 <0.2 <0,2Pb <5.0 <5.0 <0.1 <0.1 0.004-0.15 <0.1 <5Se <0.02 <0.02 <0.02 <0.02 0.05 <0.02 <0,02Cd <0.01 <0.01 <0.01 <0.01 0.0004-0.015 <0.01 <0,01Zn <2 <2 <15 <15 0.05-0.6 <2 <2Cn <0.1 <0.1 <0.1 <0.1 0.005 <0.1 <0,1Cr <0.1 <0.1 <0.05 <0.05 0.1 <0.1 <0,1Hg <0.001 <0.001 <0.001 <0.001 0.00005 <0.001 <0,001V <0.1 <0.1 <0.1 <0.1 ………….. <0.1 <0,1Co <0.05 <0.05 <0.05 <0.05 ………….. <0.05 <0,05B <1.0 <1.0 <2.0 <1.0 ………….. <3.0 <3Mo <0.01 <0.01 <0.01 <0.01 ………….. <0.01 <0,01TFCC* <1000 ………….. <1000 <1000 <10000 <200 ----Salmonella * ………….. ………….. ………….. ………….. <100000 … ----Amaebae&Gardia <1 ………….. ………….. ………….. ………….. … ----Nematodes ** <1 ………….. <1 ………….. ………….. <1 <1

*MPN/100ml, **eggs


Table 2-14: Guidelines for Reuse in Irrigation Fat and grease FOG mg/l 8Phenol Phenol mg/l <0.002


Detergent MBAS mg/l 100Total Dissolved Solids TDS mg/l 1500Total Phosphate T-PO4 mg/l 30Chloride Cl mg/l 400Sulfate SO4 mg/l 500Bicarbonate HCO3 mg/l 400Sodium Na mg/l 230Magnesium Mg mg/l 100Calcium Ca mg/l 230Sodium Adsorption Ration SAR - 9Aluminium Al mg/l 5Arsenic As mg/l 0.1Berelium Be mg/l 0.1Copper Cu mg/l 0.2Floride F mg/l 1.5Iron Fe mg/l 5.0Lithium Li mg/l 2.5(0.075 for citrus crops)Manganese Mn mg/l 0.2Molibdenum Mo mg/l 0.01Nikel Ni mg/l 0.2Lead Pb mg/l 5.0Selenium Se mg/l 0.05Cadmium Cd mg/l 0.01Zinc Zn mg/l 5.0Chrome Cr mg/l 0.1Mercury Hg mg/l 0.002Vanadium V mg/l 0.1Cobalt Co mg/l 0.05Boron B mg/l 1.0


2.4.6 Reuse standards in Lebanon

There are no standards for reuse of wastewater in Lebanon. There are only

standards for its discharge into surface water and sea water. The latter standards

were set in March 2001 in Law No.8/1, and have not been updated so far.

The effluent standards for wastewater discharge into the sea and into Surface

Water are shown in Table 2-15 and 2-16. In both tables column 1 show the

regulated pollution parameters and column 2 gives the emission limit values for

existing facilities. Emission limit values of column 2 will automatically expire when

the Barcelona LBS protocol is ratified by the Republic of Lebanon. In this case

the emission limits values of column 3 will automatically become valid for all kind

of facilities.Table 2-15: Environmental limit values for wastewater discharged into seawater

Parameter for existing facilities for new facilitiespH 5-9 6-9


Temperature 350C 350CBOD5 mg/L 100 25COD mg/L 250 125Total Phosphorus mg/L 16 10Total Nitrogen mg/L 40 30Suspended solids mg/L 200 60AOX 5 5Detergents mg/L 3 3Coliform Bacteria/100ml 2,000 2,000Salmonellae Absence AbsenceHydrocarbons mg/L 20 20Phenol index mg/L 0.3 0.3Oil and Grease mg/L 30 30Total Organic Carbon mg/L 75 75Ammonia mg/L 10 10Ag mg/L 0.1 0.1Al mg/L 10 10As mg/L 0.1 0.1Ba mg/L 10 2Cd mg/L 0.2 0.2Co mg/L 0.5 0.5Total Cr mg/L 2 2Hexavalent Cr mg/L 0.5 0.2Cu mg/L 1.5 1.5Fe mg/L 5 5Hg mg/L 0.05 0.05Mn mg/L 1 1Ni mg/L 2 0.5Pb mg/L 0.5 0.5Sb mg/L 0.3 0.3Sn mg/L 2 2Zn mg/L 10 5Active Cl2 mg/L 1 1Cyanides mg/L 0.1 0.1Fluoride mg/L 25 25Nitrate mg/L 90 90Phosphate mg/L 5 5Sulphate mg/L 1,000 1,000Sulphide mg/L 5 1

Source: Medaware, 2005b

Table 2-16: Environmental limit values for wastewater discharged into surface waters Parameter for existing facilities for new facilitiespH 5-9 6-9


Temperature 300C 300CBOD5 mg/L 100 25COD mg/L 250 125Total Phosphorus mg/L 16 10Total Nitrogen mg/L 40 30Suspended solids mg/L 200 60AOX 5 5Detergents mg/L 3 3Coliform Bacteria/100ml 2,000 2,000Salmonellae Absence AbsenceHydrocarbons mg/L 20 20Phenol index mg/L 0.3 0.3Oil and Grease mg/L 30 30Total Organic Carbon mg/L 75 75Ammonia mg/L 10 10Ag mg/L 0.1 0.1Al mg/L 10 10As mg/L 0.1 0.1Ba mg/L 2 2Cd mg/L 0.2 0.2Co mg/L 0.5 0.5Total Cr mg/L 2 2Hexavalent Cr mg/L 0.5 0.2Cu mg/L 1.5 0.5Fe mg/L 5 5Hg mg/L 0.05 0.05Mn mg/L 1 1Ni mg/L 2 0.5Pb mg/L 0.5 0.5Sb mg/L 0.3 0.3Sn mg/L 2 2Zn mg/L 5 5Active Cl2 mg/L 1 1Cyanides mg/L 0.1 0.1Fluoride mg/L 25 25Nitrate mg/L 90 90Phosphate mg/L 5 5Sulphate mg/L 1,000 1,000Sulphide mg/L 1 1

Source: Medaware, 2005b

2.4.7 Reuse standards in Morocco

The reused water is mainly raw wastewater sometimes mixed with fresh water.

The irrigated crops are mainly fodder crops (4 harvests of corn per year around

Marrakech), fruit trees, cereals and produce (growing and selling vegetables to

be eaten raw is prohibited). Morocco does not have yet any specific wastewater

reuse regulations. Reference is usually made to the WHO recommendations

(Table 2-17). While reducing its environmental impact on the conventional

receiving waters, the lack of wastewater treatment before reuse in inland cities

results in adverse health impacts. Improvement in wastewater reuse methods


and in the quality of reused water for irrigation is recognized as essential. In

karstic areas, the infiltration of wastewater affects groundwater resources to

varying degrees. Lastly, the inadequate sanitation, collection and treatment of

wastewater, mostly in small towns, are often a risk to the eutrophication of dams.

The discharge of raw wastewater to the sea without proper outfalls may affect the

development of tourism by degrading the sanitary quality of beaches and

generating unpleasant odours and aesthetics (Medaware, 2004).

Table 2-17: Use of wastewater criteria in Morocco Category A B CConditionfor realization Irrigation of

cultures to be consumed raw, sport fields, parksiii(+)

Irrigation of cereals, industrial crops, fodder crops, pastures and tree plantations

Local irrigation of cultures of category B if the farmers and public consumers are not exposed to it

Exposed groups FarmersPublicConsumers

Farmers None

Intestinal nematodesi(*)arithmetic mean of the number of eggs per liter

Absence Absence Without object

Fecal coliformesGeometric mean of the number per 100ml ii(+)

≤1000(d) No standard is recommended

Without object

Treatment process for wastewaterCapable of ensuring the required microbiological quality

A series of stabilization tanks designed to obtain the desired microbiological quality or any other equivalent treatment

Retention in the stabilization basin for 8-10 days or any other process which allows an equivalent elimination of the helminthes and the fecal coliforms

Preliminary treatment according to the irrigation technique, but at least primary decantation

i(*) Ascaris, Trichuris(whipworm) and Ankylostomaii(+) During the irrigation periodiii(+)A strict directive(<200 fecal coliforms pe 100ml) is justified for lawn with which the public can have a direct contactSource: Medaware, 2003

Table 2-18: Quality standards of water in order to be used for irrigation in Morocco Parameters Limit values

BACTERIOLOGIC PARAMETERS


1 Fecal coliforms 1000/100ml*2 Salmonella Absence in 513 Bacterium of cholera Absence in 450ml

PARASITOLOGIC PARAMETERS4 Pathogenic parasites Absence5 Eggs, Cysts of parasites Absence6 Larvae of Ankylostomides Absence7 Fluococercaires of Schistosoma haemotobium Absence

TOXIC PARAMETERS(1)

8 Mercury (Hg) in mg/l 0,0019 Cadmium (Cd) in mg/l 0,01

10 Arsenic (As) in mg/l 0,111 Total Chrome (Cr) in mg/l 0,112 Lead (Pb) in mg/l 513 Copper (Cu) in mg/l 0,214 Zinc (Zn) in mg/l 215 Selenium (Se) in mg/l 0,0216 Fluorine (F) in mg/l 117 Cyanide (Cn) in mg/l 118 Phenols in mg/l 319 Aluminium (Al) in mg/l 520 Beryllium (Be) in mg/l 0,121 Cobalt (Co) in mg/l 0,0522 Iron (Fe) in mg/l 523 Lithium (Li) in mg/l 2,524 Manganese (Mn) in mg/l 0,225 Molybdenum (Mo) in mg/l 0,0126 Nickel (Ni) in mg/l 0,227 Vanadium (V) in mg/l 0,1

PHYSICO- CHEMICAL PARAMETERS28 Total salinity (STD) mg/l* 7680

Electric conductivity (CE) mS/cm, 250C* 12TOXIC IONS (affecting sensible cultures)

29 Sodium(Na)Surface irrigation (SAR*) 9Irrigation by spraying (mg/l) 69

30 Chlorine(Cl)surface irrigation (mg/l) 350Irrigation by spraying (mg/l) 105

31 Boron (B) (mg/l) 3VARIOUS PARAMETERS (affecting sensible cultures)

32 Temperature(0C) 3533 pH 6,5-8,434 Suspended solids in (mg/l)

Gravitational irrigationLocal irrigation and irrigation by spraying

2,000100

35 Nitrates (N-NO3) in (mg/l) 3036 Bicarbonate (HCO3) (Irrigation by spraying mg/l) 51837 Sulphates (SO4

-2) in (mg/l) 250*1,000CF/100ml for cultures intended for raw consumption*If electric conductivity (CE) exceeds 3mS/cm, severe restrictions are applied to water when it is to be used for irrigation, but the 50% of the potencial yield can be irrigated with water of 8,7mS/cm(in the case of Barley)*SAR= Sodium adsorption ratio (coefficient of sodium absorption)

Source: Medaware, 2003

2.4.8 Reuse Standards in Palestine


For a long time Palestine did not have any specific wastewater regulation,

References were usually made to the WHO recommendations or to the

neighboured countries standard (Egypt, Jordan). Recently the Environment

Quality Authority with coordination of Palestinian ministries and universities has

established specific wastewater reuse regulations. The draft of Palestinian

legislation for reuse of treated wastewater is still under study in the Palestinian

Standard Institute.

Most of the reuse projects in Gaza Strip and West Bank are using treated

wastewater for irrigation according to WHO and FAO guidelines. The WHO

guidelines are strict in respect of the requirements to keep the number of eggs

(ascaris and hookworms) in effluent below one egg per liter whether the effluent

is used for restricted or unrestricted irrigation using surface and sprinkler

irrigation. This is not applicable in case of restricted irrigation where exposure of

workers and public does not occur.

On the other hand these guidelines are relaxed in the case of faecal coliforms, as

no standard is recommended for these pathogens in the case of restricted

irrigation and 1000 or less per 100 ml in the case of unrestricted irrigation. This is

based on the assumption that the treatment that results in effluent of having less

than one egg per liter of intestinal will be practically safe in case of virus and

bacteria.

In addition to the microbiological quality requirement of effluent used for irrigation

attention also is given to quality parameters of ground water contamination and

of soil structure and crop productivity. These include the nutrients content of the

effluent (mainly nitrate), total dissolved solids, and sodium adsorption ratio and

toxic elements (boron and heavy metals), which is available at FAO guidelines

(PWA, 2000).

2.4.9 Reuse Standards in Spain


Spain has a national legislation and a number of regional regulations. Draft

guidelines were proposed in 1995, taking an approach closer to the California

standards than to those of the WHO (Table 2-19).

The national water law (Ley de Aquas, 29/1985) merely foresees that the

government will establish the basic conditions for the direct use of wastewaters

according to the treatment processes, water quality and foreseen uses.

A Royal Degree to extend this existing Law was published in 2001. The Degree

foresees a standard of 1 nematode egg per litre for all types of irrigation and 10

faecal coliforms per 100ml for unrestricted irrigation. For restricted irrigation the

faecal coliform standards becomes 200 per 100ml and in the case of irrigations of

cereals, industrial crops, fodder crops and pastures, it becomes 500 faecal

coliforms per 100ml. Limits on chlorine are also foreseen. Specific standards for

heavy metals must be respected for the reuse of industial wastewaters.

Table 2-19: Draft microbiological quality guidelines and criteria for irrigation in the proposed Spanish national regulation (1995) Reuse applicationa Intestinal nematodes Faecal or total

coliformsWastewater treatment requirements

Crops that can be eaten raw <1/l < 10/100 mL

Fruit trees and crops that are eaten cooked <1/l < 200/100 mL Secondary treatment

and disinfectionIndustrial crops, cereals, fodder crops and pastures

<1/l< 500/100 mL Secondary treatment

and disinfection

Lawns, wooded areas, and other areas with limited public access

<1/l

< 200/100 mL Secondary treatment and disinfection

Parks, public gardens, lawns, golf courses and other areas with direct public exposure

<1/l

< 10/100 mL Secondary treatment, filtration or equivalent treatment and disinfection

a In the case of spray irrigation, minimum distances to inhabited areas and public ways will be fixed.

Source: Bontoux, 2000


Also a few regional legislations and standards do exist in Andalusia, Baleares,

Catalonia and Canarias. Andalusia (Castillo Martín et al., 1994) and Catalonia

(Salgot et al., 1994) have issued comprehensive wastewater reuse guidelines

essentially following those of the WHO and are encouraging the practice.

Catalonia has guidelines containing limit values for boron, cadmium, olybdenum

and selenium, all relevant for the health of irrigated crops (Salgot et al., 1994).

The microbiological standards are those of the WHO.

Andalusia also has recommendations dating from 1994, largely following the

French approach. However these quidelines specifically exclude the reuse of

wastewater for potable water, street cleaning, municipal heating and cooling, and

the cleaning of urban premises, as well as for the washing the transport of

materials. Groundwater recharge is also restricted. Overall the permitted types of

reuse fall into seven categories.

2.4.10 Reuse Standards in Turkey

Water reuse has been officially legitimized in 1991 through the Regulation for

irrigational wastewater reuse issued by the Ministry of Environment (Medaware,

2003b). Since then, there have been no changes and revisions of the regulation,

however, the applications have not been satisfactorily realized so far.

The most important criteria for evaluating the suitability of treated wastewater for

irrigation use are: public health aspects, salinity (especially significant in arid

regions), heavy metals and harmful organic substances. In addition to standards,

regulations can include best practices for wastewater treatment and irrigation

techniques as well as regarding crops and areas to be irrigated.

In Turkey, the WHO standards have been adopted except the limits for the

intestinal nematodes and the residual chlorine. Concerning the microbiological

standards, the Turkish regulation consists of only faecal coliform parameter and,

it seems to be insufficient and needs to be revised in terms of health aspects. Table 2-20: Turkish water quality criteria for irrigation, according to classes


Quality CriteriaClass I

(Perfect)Class II

(Satisfactory)Class III(Usable)

Class IV(Usable with

care)

Class V(Improper harmful)

EC25 (microhos at 25 oC) ×106 0-250 250-750 750-2,000 2,000-3,000 >3,000Sodium (Na, %) <20 20-40 40-60 60-80 >80Sodium Adsorption Ratio (SAR) <10 10-18 18-26 >26Residual Sodium Carbonate (RSC) in meq/l or mg/l

>1.25<66

1.25-2.566-133

>2.5>133

Chloride (Cl-) in meq/l or mg/l 0-40-142

4-7142-249

7-12249-426

12-20426-710

>20>710

Sulphate (SO4=) in meq/l or mg/l 0-4

0-1924-7

192-3367-12

336-57512-20

575-960>20

>960Total Salt Concentration (mg/l) 0-175 175-525 525-1,400 1,400-2,100 >2,000Boron Concentration (mg/l) 0-0.5 0.5-1.12 1.12-2.0 >2.0 -Class of Irrigation Water * C1S1 C1S2,

C2S2, C2S1

C1S3, C2S3,

C3S3, C3S2

C3S1

C1S4, C2S4,C3S4, C4S4,C4S3, C4S2

C4S1

-

NO3--N or NH4

+-N (mg/l) 0-5 5-10 10-30 30-50 >50Faecal Coliform** 1/100 ml (CFU in 100 ml)

0-2 2-20 20-100 100-1,000 >1,000

BOD5 (mg/l) 0-25 25-50 50-100 100-200 >200TSS (mg/l) 20 30 45 60 >100pH 6.5-8-5 6.5-8.5 6.5-8.5 6.5-9 <6 or >9Temperature (oC) 30 30 35 40 >40

* there exists a diagram that indicates the relationship between SAR and electrical conductivitiy** varies according to type of plantation

Source: Medaware, 2005c

Boron concentrations are known to be important for Turkey’s conditions as the

country is rich in boron sources. The table stating the boron concentrations in

terms of irrigation water is given below in Table 2-21.

Table 2-21: Classification of irrigation water with respect to resistance of plants to boron mineral Classification of irrigation water

Boron concentration (mg/l) sensitive

plants*

Boron concentration (mg/l) semi-sensitive

plants**

Boron concentration (mg/l)tolerable plants***

I < 0.33 < 0.67 < 1.0II 0.33-0.67 0.67-1.33 1.00-2.00III 0.67-1.00 1.33-2.00 2.00-3.00IV 1.00-1.25 2.00-2.50 3.00-3.75V > 1.25 > 2.50 > 3.75

*e.g. walnut, lemon, fig, apple, grape and bean.**e.g. barley, wheat, maize, oats, olive and cotton.***e.g. sugar beet, clover, horse bean, onion, lettuce and carrot. Source: Medaware, 2005c

In the same Part, a table exists on maximum allowable concentration of heavy


metals and toxic elements in irrigation water. It is given below in Table 2-22 and

is adopted from EPA.

There are two more Tables on reuse of treated effluent for irrigation purposes.

Table 2-23 states the technical limitations and related on reuse of water in

irrigation and Table 2-24 indicates the suitability of treated domestic wastewater

in irrigation without disinfection. Both tables are shown in Table 2-23 and Table

2-24 respectively.

Table 2-22: Maximum allowable concentration of heavy metals and toxic elements in irrigation, water in Turkey Elements Max. total amount to

be given to unit area of land(kg/ha)

Maximum allowable concentration in every type of soil and under continuous irrigation

(mg/l)

Maximum allowable concentration in clayey

soil (pH: 6.0-8.5) irrigation less than 20

years (mg/l)Aluminum 4,600 5.0 20.0Arsenic 90 0.1 2.0Beryllium 90 0.1 0.5Boron 680 specified in Table 9 of

the bulletin2.0

Cadmium 9 0.01 0.05Chromium 90 0.1 1.0Cobalt 45 0.05 5.0Copper 180 0.2 5.0Fluoride 920 1.0 15.0Iron 4,600 5.0 20.0Lead 4,600 5.0 10.0Lithium * - 2.5 2.5Manganese 920 0.2 10.0Molybdenum 9 0.01 0.05*/**1

Nickel 920 0.2 2.0Selenium 18 0.02 0.02Vanadium - 0.1 1.0Zinc 1,840 2.0 10.0

* 0.075 mg/l is recommended for irrigation of citrus fruits*/** allowable concentration in only acidic clay soil with high iron content


Table 2-23: The technical limitations and related basis on reuse of water in irrigation


Type of crops Technical limitationsOrchard and vineyards -No spray irrigation

-Fruits falling on ground cannot be eaten-Faecal coliform <1,000/100 ml

Fibrous and seed crops -Surface or spray irrigation-Disinfection and biological treatment are required for spray irrigation-Faecal coliform <1000/100 ml

Feed crops, flowers, vegetables which are not eaten raw

-Surface irrigation-Minimum mechanical treatment


Table 2-24: Suitability of treated domestic wastewater in irrigation without disinfection Arable land

Meadow and

pasture

Vegetables Feed crop

Fruit production

Forestry &

woodlandEffluent of biological treatment plant or pre-treatment effluent (with 2 hours detention time sedimentation tank)

(+) for both NP

& P

(+) for both NP & P

(-) for both NP & P

(+) for NP

(-) for P

(-) for both NP & P (+)

Effluent of aerobic stabilization ponds and lagoons

(+) for NP

(-) for P

(+) for NP(-) for P

(-) for both NP & P

(+) for NP

(-) for P

(-) for both NP & P (+)

NP= no plantationP= plantation (with or with out fruits)Source: Medaware, 2005c

2.5 Comparison of reuse standards and standards for irrigation in various countries

Different approaches for the protection of public health and the environment have

been developed by different countries, but the major determining factor in

choosing a regulatory strategy is economics, specifically the cost of treatment

and monitoring. Most developed countries have established conservatively low

risk guidelines or standards based on a high technology/high-cost approach (e.g.

California standards). Due, however, insufficient operational experience, OM&R

costs, and regulatory control, high standards and high-cost techniques do not

always guarantee low risk and can have adverse effects. A number of developing

countries advocate another strategy of controlling health risks by adopting a low

technology/low-cost approach based on the WHO recommendations. Table 2-25

summarises guidelines and mandatory criteria for reclaimed water use in a

variety of U.S. states and other countries and regions.


The principle behind guidelines is that, better health protection can be achieved

by not only implementing stringent water quality limits but also by defining other

appropriate practices that could provide additional barriers for pathogens

depending on the type of reuse. Such an approach has been proposed in the

new Israeli standards of 1999 (EPA, 2004).

Table 2-25: Summary of Water Recycling Guidelines and Mandatory Standards in the United States and Other Countries



2.6 EU environmental legislation on water quality

The legal status of wastewater reuse is not uniform across Europe. Many

European countries and northern European countries do not have specific

regulations. Some of them have national regulations, laws, recommendations

and other. So far no regulation of wastewater reuse exists at a European level.

The only reference made by the EU on the matter of wastewater is Article 12 of

the European Wastewater Directive (91/271/EEC).

However, in general, water is one of the most comprehensively regulated areas

of EU environmental legislation. Early European water policy began in the 1970s

with the First Environmental Action Programme in 1973 followed by a first wave

of legislation, starting with the 1975 Surface Water Directive and arriving in the

1980 with the Drinking Water Directive. This first wave of water legislation

included water quality standard legislation on fish waters (1978), shellfish waters

(1979), bathing waters (1976) and groundwaters (1980). In the field of emission

limit value legislation the Dangerous Substances Directive (1976) and its

Daughter Directives on various individual substances were adopted.

A second wave of water legislation followed a review of existing legislation and

an identification of necessary improvements. This phase of water legislation

included the Urban Waste Water Treatment Directive (1991) and the Nitrates

Directive (1991). Other elements identified were revisions of the Drinking Water

and Bathing Water Directives to bring them up to date (proposals for revisions

being adopted in 1994 and 1995 respectively), the development of a

Groundwater Action Programme and a 1994 proposal for an Ecological Quality of

Water Directive. In developing its environmental policy, the European Union uses

two main tools:

1. Regulations (documents of general importance, binding and directly

applicable in the whole European Union);

2. Directives (documents not directly applicable but needing an adequate,

binding integration in every national body of laws, generally in 18-36 months).


Therefore the European legislation is characterized by a numerous quidelines

concerning water pollution and water quality. In the following diagram (Figure 2-

1) the EU Water Quality Standards are shown. The Water Framework Directive

2000/60/EC, incorporates the following:

1. The Surface Water Directive (Directives 75/440/EEC and 79/869/EEC). The

Surface Water Directive helps ensure clean drinking water by protecting those

rivers, lakes and reservoirs used as drinking water sources.

2. The Bathing Water Directive (Directive 76/160/EEC). The Bathing Water

Directive safeguards the health of bathers and maintains the quality of

bathing waters.

3. the Dangerous Substances Directive (Directive 76/464/EEC, as amended by

Directive 91/692/EEC, and "daughter" Directives 82/176/EEC, 83/513/EEC,

84/156/EEC, 84/491/EEC and 86/280/EEC)

4. the Fish Water Directive (Directive 78/659/EEC)

5. the Shellfish Water Directive (Directive 79/923/EEC)

The Fish Water Directive and the Shellfish Water Directive's objectives are to

protect fresh water bodies capable of supporting fish life and to protect coastal

and brackish waters in order to support shellfish populations and to prevent

contamination of the harvested product respectively.

The following Directives are not part of the Water Framework Directive

2000/60/EC:

6. the Groundwater Directive (Directive 80/68/EEC) – currently under revision

7. the Urban Wastewater Treatment Directive (Directive 91/271/EEC):

recommended reuse of treated effluents. The directive specified standards for

discharge into fresh water and their catchment but no standards for reuse. It

provides though regulations and permits for all discharge.

8. the Nitrate Directive (Directive 91/676/EEC)

9. the Drinking Water Directive of 15 July 1980 (Directive 80/778/EEC). The

Drinking Water Directive's objective is to safeguard human health by

establishing strict standards for the quality of water intended for human

consumption. The Drinking Water Directive of 1980 has so far provided the


http://www.italocorotondo.it/tequila/module4/legislation/drink_water_directive_80.htm

http://www.italocorotondo.it/tequila/module4/legislation/EC_water_laws.htm#Council%20Directive%2084/491/EEC




consumer security for drinking water quality throughout the EU. However, it

was both out of date as concerns scientific/technical basis (original proposal

was made in 1975) and the managerial approach.

10. the Drinking Water Directive of 3 November 1998 (Directive 98/83/EC). A new

Directive on drinking water (Directive 98/83/EC) was developed aiming to:

review of parametric values, and where necessary strengthening them in

accordance with the latest available scientific knowledge (WHO Guidelines,

Scientific Committee on Toxicology and Ecotoxicology)

increase of transparency: the point of use of water (the "tap") is the point of

compliance with the quality standards; reference values are referred to

ISO/CEN standards; reports on quality are obligatory; consumer must be

informed on drinking water quality and measures that they can take to comply

with the requirements of the Directive -in particular for lead- when the non-

compliance is because of the domestic distribution system (internal pipes,

plumbing etc)

The main changes in parameters are:

66 parameters in the old directive have been reduced to 48 (50 for bottled

waters)in the new one, including 15 new parameters;

Lead standards are reduced from 50μg/l to 10μg/l. Moreover 15 years

transition period is allowed for replacing lead distribution pipes.

Values for individual pesticides and for total pesticides are retained (0.1μg/l /

0.5μg/l), plus additional, more stringent ones introduced for certain pesticides

(0.03μg/l)

Copper standards are reduced from 3 to 2 mg/l

Standards are introduced for new parameters like trihalomethanes,

trichloroethene and tetracholoroethene, bromate, acrylamide etc A presentation

of the parametric values (microbiological, chemical, indicator parameters) and

quality characteristics of water of the following Directives 98/83/EC, 76/160/EEC,

75/440/EEC are shown below. Standards of Drinking Water directive affects the


http://www.italocorotondo.it/tequila/module4/legislation/drink_water_directive_98.htm

quality of the domestic sewage e.g. conductivity, boron, nitrates (salt content

affects crops, many crops are sensitive).Fi

gure 2-1: EU Water Quality Standards


Water Framework Directive2000/60/EC

Directive 98/83/EC (quality of water indended for human consumption) Table 2-26: Parameters given in Directive 98/83/EC

PARAMETERS AND PARAMETRIC VALUESPart A: Microbiological parameters

Parameter Parametric value(number/100ml)

Escherichia coli(E.coli) 0Enterococci 0The following applies to water offered for sale in bottles or containersParameters Parametric valueEscherichia coli(E.coli) 0/250mlEnterococci 0/250mlPseudomonas aeruginosa 0/250mlColony count 220C 100/mlColony count 370C 20/ml

Part B: Chemical parameters

Parameters Parametric value UnitAcrylamide 0.10 μg/lAntimony 5.0 μg/lArsenic 10 μg/lBenzene 1.0 μg/lBenzo(a)pyrene 0.010 μg/lBoron 1.0 mg/lBromate 10 μg/lCadmium 5.0 μg/lChromium 50 μg/lCopper 2.0 mg/lCyanide 50 μg/l1,2-dichloroethane 3.0 μg/lEpichlorohydrin 0.10 μg/lFluoride 1.5 mg/lLead 10 μg/lMercury 1.0 μg/lNickel 20 μg/lNitrate 50 mg/lNitrite 0.50 mg/lPesticides 0.10 μg/lPesticides-Total 0.50 μg/lPolycyclic aromatic hydrocarbons 0.10 μg/lSelenium 10 μg/lTetrachloroethene and Trichloroethene 10 μg/lTrihalomethanes-Total 100 μg/lVinyl chloride 0.50 μg/l


Part C: Indicator parameters

Parameters Parametric value UnitAluminium 200 μg/lAmmonium 0.50 mg/lChloride 250 mg/lClostridium perfringens(including spores)

0 Number/100ml

Colour Acceptable to consumers and no abnormal change

Conductivity 2500 μS cm-1 at 200CHydrogen ion concentration ≥6.5 and ≤9.5 pH unitsIron 200 μg/lManganese 50 μg/lOdour Acceptable to consumers and

no abnormal changeOxidisability 5.0 mg/l O2

Sulphate 250 mg/lSodium 200 mg/lTaste Acceptable to consumers and

no abnormal changeColony count 220 No abnormal changeColiform bacteria 0 Number/100mlTotal organic carbon(TOC) No abnormal changeTurbidity Acceptable to consumers and

no abnormal change

In order to protect the environment and public health it is necessary to reduce the

pollution of bathing water and to protect such water against further deterioration.

The quality requirements for bathing water according to the Bathing Directive

76/160/EEC are shown in the following table (Table 2-27).

Table 2-27: Quality requirements for bathing water

Microbiological parameters G ITotal coliforms/100ml 500 10000Faecal coliforms/100ml 100 2000Faecal streptococci/100ml 100 -Salmonella/litre - 0Enteroviruses PFU/10litres - 0Physico-chemical parameters G IpH - 6-9(0)

Colour - No abnormal change in colour(0)

Mineral oils mg/litre ≤0.3 No film visible on the surface of the water and no odour

Surface-active substances reacting with methylene blue mg/l (Lauryl sulphate)

≤0.3 No lasting foam

Phenols mg/l (phenol indices) C6H5OH ≤0.005 No specific odour ≤0.05Transparency 2 1(0)


Dissolved oxygen % saturation O2 80 to 120 -Tarry residues and floating materials such as wood, plastic articles, bottles, containers of glass, plastic, rubber or any other substance. Waste or splinters

Absence -

Ammonia mg/litre NH4 - -Nitrogen Kjeldahl mg/litre N - -Other substances regarded as indications of pollution

G I

Pesticides mg/litre (parathion, HCH, dieldrin) - -Heavy metals (mg/litre) such as: As, Cd, Cr, Pb, Hg - -Cyanides mg/litre Cn - -Nitrates mg/litre NO3 and phosphates PO4 - -G=guide, I=mandatory, PFU – plaque forming units

(0) provision exists for exceeding the limits in the event of exceptional geographical conditions

Directive 75/440/EEC concerning the quality required of surface water intended for the abstraction of drinking water in the Member States. In Table 2-28 the characteristics of surface water intended for the abstraction of

drinking water are shown below. In the Table 2-28 there are three categories of

A1, A2, A3 (it’s the transformation of surface water of these categories into

drinking water). A definition of categories is explained below:

Category A1: Simple physical treatment and disinfection (rapid filtration and

disinfection) Category A2: Normal physical treatment, chemical treatment and disinfection

e.g. pre-chlorination, coagulation, flocculation, decantation, filtration,

disinfection (final chlorination). Category A3: Intensive physical and chemical treatment, extended treatment

and disinfection e.g.chlorination to break-point, coagulation, flocculation,

decantation, filtration, adsorption (activated carbon), disinfection (ozone, final

chlorination).

Table 2-28: Characteristics of surface water intended for the abstraction of drinking waterParameters A1

GA1I

A2G

A2I

A3G

A3I

1 pH 6.5 to 8.5

5.5 to 9 5.5 to 9

2 Coloration (after simple filtration) mg/l Pt scale

10 20(O) 50 100(O) 50 200(O)

3 Total suspended solids mg/l SS 254 Temperature °C 22 25(O) 22 25(O) 22 25(O)5 Conductivity μs/cm-1 at 200C 1000 1000 1000


6 Odour (dilution factor at 250C 3 10 207* Nitrates mg/l NO3 25 50(O) 50(O) 50(O)8(1) Fúorides mg/l F 0,7 to 1 15 0,7 to 1 0,7 to 179 Total extractable organic chlorine mg/l

Cl10 Dissolved iron mg/l Fe 0,1 0,3 1 5 1 511* Manganese mg/l Mn 0,05 0,1 112 Copper mg/l Cu 0,02 0,05(O) 0,05 113 Zinc mg/l Zn 0,5 3 1 5 1 514 Boron mg/l B 1 1 115 Beryllium mg/l Be16 Cobalt mg/l Co17 Nickel mg/l Ni18 Vanadium mg/l V19 Arsenic mg/l As 0,01 0,05 0,05 0,05 0,120 Cadmium mg/l Cd 0,001 0,005 0,001 0,005 0,001 0,00521 Total chromium mg/l Cr 0,05 0,05 0,0522 Lead mg/l Pb 0,05 0,05 0,0523 Selenium mg/l Se 0,01 0,01 0,0124 Mercury mg/l Hg 0,0005 0,001 0,0005 0,001 0,0005 0,00125 Barium mg/l Ba 0,1 1 126 Cyanide mg/l Cn 0,05 0,05 0,0527 Sulphates mg/L SO4 150 250 150 250(O) 150 250(O)28 Chlorides mg/l Cl 200 200 20029 Surfactants(reacting with methyl blue)

mg/l(laurylsulphate)0,2 0,2 0,5

30 Phosphates 0,4 0,7 0,731 Phenols (phenol index) paranitraniline

4 aminoantipyrine mg/l C6H5OH0,001 0,001 0,005 0,01 0,1

32 Dissolved or emulsified hydrocarbons(after extraction by petroleum ether) mg/

0.05 0.2 0.5 1

33 Polycyclic aromatic hydrocarbons mg/l 0.0002 0.0002 0.00134 Total pesticides (parathion, BHC,

dieldrin)mg/

0.001 0.0025 0.005

35 Chemical oxygen demand (COD) mg/l O2

30

36 Dissolved oxygen saturation rate %O2 >70 >50 >3037 Biochemical oxygen demand (BOD5)

(at 20 °C without nitrification) mg/l O2

<3 <5 <7

38 Nitrogen by Kjeldahl method (exceptNO3) mg/l N

1 2 3

39 Ammonia mg/l NH4 0.05 1 15 2 4(0)40 Substances extractable with chloroform

mg/l SEC01 02 05

41 Total organic carbon mg/l C42 Residual organic carbon after

flocculationand membrane filtration (5 μ) TOC mg/l C

43 Total coliforms 37 °C /100 ml 50 5000 5000044 Faecal coliforms /100 ml 20 2000 2000045 Faecal streptococci /100 ml 20 1000 1000046 Salmonella Not

present in

5000ml

Not present

in 1000ml

=mandatory, G=guide, O=exceptional climatic or geographical conditions


2.7 General conclusions and comparison

To understand better Table 2-29 for example in Directive 76/160/EEC for faecal

coliform/100ml the 100(g) is the guide value and the 2000 is the mandatory

value. For Directive 75/440/EEC it depends from the category for example for

category A1 the guide value is 20 faecal coliforms/100ml. Directive 98/83/EC

does not have value for faecal coliform neither does California guidelines. In

WHO guidelines faecal coliforms must be ≤1000/100ml and in U.S.EPA

guidelines the value depends from the reuse type and from the state.

Table 2-29: General conclusions and comparison between the available reuse guidelines of WHO, recycling criteria of California, U.S.EPA and the following Directives (76/160/EEC, 75/440/EEC, 98/83/EC)

FaecalColiforms

(CFU/100ml)

TotalColiforms

(CFU/100ml)

HelminthEggs

BOD5 Turbidity(NTU)

TSS(ppm)

pH

76/160/EEC 100(g) 500(g) ---- ---- 2(g) ---- 6-9

2,000(m) 10,000(m) 1(m)

75/440/EEC 20 (1) 50(1) ---- <3(1) ---- 25(1) 5.5 -92000(2) 5000(2) <5(2)

20000(3) 50000(3) <7(3)

98/83/EC ---- ---- ---- ---- Acceptable to

consumers

---- ----

California ---- 2,2 ---- ---- 2 ---- ----WHO ≤1000 ---- ---- ---- ---- ---- ----U.S.EPA (*) (*) (*) (*) (*) (*) (*)(1) category A1 as mentioned in table 3-12(2) category A2 as mentioned in table 3-12(3) category A3 as mentioned in table 3-12(*) it depends from the type of reuse and from the state (see Tables 2-4, 2-5, 2-6, 2-7)


3. Pathogens and Public Health

The most important constraint to wastewater reuse has most often been the

concern for the public health. Wastewater does carry pathogenic organisms and,

in general, modern treatment methods (for example, activated sludge) were not

designed to eliminate them. Wastewater disinfection will eliminate them, but it is

relatively costly and beyond the technological and financial capabilities of many

regions in developing countries. Organisms that can survive wastewater,

treatment (without disinfection) include bacteria, protozoa, helminths, and

viruses. Most of these pathogens affect the human body only through ingestion

of waste-contaminated water and food.

The major factors that control the degree of microbial health risk include:

(a) The ability of pathogens to survive or multiply in

the environment

(b) The dose required for infection

(c) The need for, and the presence or absence of,

intermediate hosts and

(d) The susceptibility of the person at risk (constant

exposure may have created (immunity).

These factors are summarized in Table 3-1 which also show the persistence of

various pathogens in the environment. Pathogens affect varied population groups

differently for example consumers of raw vegetables are at greater risk than

those who cook their vegetables. Workers in wastewater-irrigated fields are at

greater risk than those working elsewhere. Some groups may not be affected at

all. It is therefore important to aim health-protection measures at specific exposed

groups.

When we think about reuse of wastewater treatment we think also about the

enteric microorganisms. These microorganisms are responsible for the 90%

waterborne diseases that appear in USA from 1971 until 1994, and many people


affected. The illnesses included infectious hepatitis, cryptosporidiosis, giardiasis,

typhoid fever and gastroenteritis.

Table 3-1: Epidemiological characteristics of enteric pathogens in terms of their effectiveness in causing infections through wastewater irrigation

Pathogen Persistence in environment

Minimum infective

doseImmunity

Concurrent routes of infection

Latency/soil development

stage

Viruses medium low longmainly home

contact and food and water

no

Bacteria Short to Medium Medium to high

short to Medium

mainly home contact and food

and waterno

Protozoa short Low to medium None to little

mainly home contact and food

and waterno

Helminths long low None to littleMainly soil

contact outside home and food

yes

Source: Gerba et al., 1975

The source of these pathogenic microorganisms might be:

The faecal material of infected individuals

Urine

Numbers and types of pathogens vary both spatially and temporally, depending

on the disease incidence in the population producing the wastewater season,

water use, economic status of population and of course from the quality of

potable water (Rose and Carnaham,1992).

3.1 Pathogenic Microoganisms

Microbial pathogens that are present in wastewater can be divided into four

groups: bacteria, viruses and the pathogenic protozoan and helminths. The

enteric are the majority of pathogens because they are excreted in faecial matter

and contaminate the environment.

In Table 3-2 an example of the different microbial pathogens and the major

diseases they cause are given.


Table 3-2: Microbial pathogens detected in untreated wastewaters

Microbial type Major diseases Concetration in wastewaters

Infectious dose

VirusesEnterovirusesPoliovirus

Enterovirus

Echovirus

Coxsackievirus

Hepatitis A virus

Poliomylitis

Gastroenteritis, heart

Anomalies, meningitis

Hepatitis

Medium to High LowAdenovirus Respiratory disease, conjuctivitis

Reovirus Not clearly established

Calicivirus

Norwalk agent

SSRV

Gastroenteritis

Gastroenteritis,

Diarrhea, vomiting, fever

Rotavirus Gastroenteritis

Astrovirus Gastroenteritis

BacteriaVibrio cholerae

Salmonela typhi

Enteropathogenic E.coli

Campylobacter jejunei

Shigella dysinterae

Yersinia enterocolitica

Cholera

Typhoid, Salmonellosis

Gastroenteritis

Gastroenteritis

Dysentery

Yersiniosis

Medium to High

High

High

High

High

Low

High

Protozoa

Giardia intestinalis

Cryptosporidium

Parvum

Entamoeba histolytica

Giardiasis

Diarrhea, fever

Amoebic dysentery

Low to High

Low

Low

Low

Helminths

Ascaris lumbricoides

(Round worm)

Ancylostoma spp.

(Hook worm)

Trichuris trichiura

(Wrip worm)

Strongiloides stercoralis

Ascariasis

Ancylostomiasis

Trichuriasis

Strongyloidasis

Low

Low

Low

Low

Low

Source: Toze, 1997


3.1.1 Bacteria

The simplest of cells are the procaryotic cells,

organisms which have a nuclear membrane. The

Bacteria are the best known and most studied

procaryotes. Procaryotic cells have three

architectural regions (Figure 3-2): appendages

(proteins attached to the cell surface) in the form

of flagella and pili; a cell envelope consisting of a

capsule, cell wall and plasma membrane; and a cytoplasmic region that contains

the cell genome (DNA) and ribosomes. Bacteria are the most common of the

microbial pathogens found in wastewater. Many of them are enteric in origin;

however bacterial pathogens which cause non-enteric illnesses (Legionella spp.,

Mycobacterium spp., and Leptospira) have also been detected in wastewaters

(Wilson and Fujioka 1995; Fliermans 1996; Neuman et al. 1997,). Bacteria are

one-celled organisms visible only with a microscope. They're shaped like short

rods, spheres or spirals (Figure 3-1). They're usually self-sufficient and multiply

by subdivision. Their size is between 0.5–5μm.

Many bacteria, however, prefer the mild environment of a healthy body. Not all

bacteria are harmful. In fact, less than 1 percent of bacteria cause disease, and

some bacteria that live in human’s body are actually of benefit. For instance,

Lactobacillus acidophilus, a harmless bacterium that resides in humans’

intestines, helps the food digestion, destroys some diseases and provides

nutrients to humans’ body. But when infectious bacteria enter the human body,

they can cause illness. They rapidly reproduce, and many produce toxins -

powerful chemicals that damage specific cells in the tissue they've invaded.

That's what makes people ill.

The most common diseases that bacterial pathogens cause in wastewater are

gastrointestinal infection. These infections include diarrhea, cholera, caused by


Figure 3-1: Bacterium

Vibrio cholera and salmonellosis caused by Salmonella species, and dysentery

caused by various Shigella spiecies. Shigella has a short life time and is spread

by contact person-to-person. Typhoid, a disease cause by Salmonella typhiand

has been traced in food stuffs irrigated with wastewater (Bryan, 1977).

Acute Enteritis is caused by the campylobacter, Helicobacter and Arcobacter.

Non-enteric bacterial diseases transmitte by pathogens present in wastewater

include legionellosis a potencially fatal pneumonia which is caused by Legionella

species.

Other

bacteria

that had

been

isolated

from raw

wastewater

and are

less

important

are: Vibrio, Mycobacterium, Clostridium, Leptospira and Yersinia. They do not

usually cause any diseases because their concentrations are too low.

Campylobacter coli is the cause of diarrhea in man. Human faecal material

contains up to 1012 bacteria /g. Most of them are not pathogenic. But an infected

person may excrete high numbers of pathogenic bacteria in their faeces. These

pathogens are transmitted through contaminated water and food and with direct

contact with an infected individual.

3.1.2 Viruses

Viruses are the most important and the most

hazardous of the pathogens found in wastewater. In

its simplest form, a virus is a capsule that contains


Figure 3-2: Procaryotic cell

Figure 3-3: Virus

genetic material - DNA or RNA (Figure 3-3). The main mission of a virus is to

reproduce. However, unlike bacteria, viruses aren't self-sufficient because they

need a suitable host to reproduce and are even tinier than bacteria. Untreated

wastewater can contain a range of viruses which are pathogenic to humans.

Viruses are more infectious, more resistant to treatment processes and require

smaller doses to cause infection than most of other pathogens. They enter the

environment through faecal contamination from infected hosts. The most

commonly found in wastewater are the enteroviruses.

Enteroviruses are small, sigled-stranded RNA viruses and include the poliovirus

types 1 and 2, multible strains of echovirus, enterovirus and coxsackievirus. The

enteroviruses are known to cause a wide range of diseases in humans including

poliomyelitis, upper respiratory infections, acute gastroenteritis, aseptic

meningitis, pericarditis, myocarditis, and viral exanthema, conjunctivitis, and

hepatitis.

Other viruses that have been detected in wastewaters include adenoviruses,

rotaviruses, reoviruses, astroviruses, and caliciviruses such as Norwalk virus and

other small round structured viruses. These viruses can cause a range of

diseases such as: acute gastroenteritis, diarrhoea, pneumonia. The most

infectious of all enteric viruses are the rotaviruses and if present in wastewater

are considered to be a high health risk. Small children are the most sensitive

group of population and have the highest infection rate from these viruses. This

group of population is more at risk because maybe a possibility for developing

the more rare forms of diseases caused by these viruses. Viruses and other

pathogens that exist in wastewater used for irrigation do not get into the fruits or

vegetables unless their skin is broken.

3.1.3 Protozoan

Protozoans are single-celled organisms and can live within humans body as a

parasite and they are transmitted by faecally contaminated food and water

(Figure 3-4). Many protozoans are harmless. Others cause disease, such as the


1993 Cryptosporidium parvum invasion of the Milwaukee water supply, sickening

more than 400,000 people. Often, these organisms spend part of their life cycle

outside of humans or other hosts, living in food, soil, water or insects.

There are a number of them that have been isolated

from wastewater sources. The most important of them

is the protozoan Entamoeba histolytica, which is

responsible for amoebic dysentery and amoebic

hepatitis, Giardia intestinalis, and Cryptosporidium

parvum. The three of them are all enteric pathogens

and have been detected in wastewater which has been

contaminated with faecal material. Infection from the

three can occur after consumption of food or water

which has been contaminated with the cysts or oocysts.

Entamoeba histolytica can be detected in all parts of the world, although it is

more prevalent in tropical regions (Feachem et al., 1983). Cryptosporidium

parvum is connected with a number of outbreaks involving drinking water. The

most serious of these outbreaks was in Milwaukee, Wiskonsin, where it was

estimated that at least 400,000 people became infected (MacKenzie et al.,1994).

3.1.4 Helminths

Helminths are multi-cell parasitic worms the nematodes

(roundworms), the trematodes (flukes), and the

cestodes (tapeworms) are common intestinal parasites

which, like the enteric protozoan pathogens, are usually

transmitted by the faecal- oral route. Helminths have

complex life circles. Helminths parasites detected in

wastewaters include the round worm (Ascaris

lumbricoides), the hook worm (Ancylostoma

duodenale), and the whip worm (Trichuris trichura).


Figure 3-4: Protozoan

Figure 3-5: Helminth

(Roundworm)

The most common helminths are tapeworms and roundworms (Figure 3-5). The

largest of the roundworms range in length from 6 to 14 inches. Helminths exist in

two forms. The first form is an actively growing larva or worm. The larva is found

inside the definitive host and produces eggs or ova. The egg or ovum is the

second form and leaves the host in faecal waste. The ovum is or develops a

protective structure that is resistant to adverse conditions and has the ability to

infect a new host.

The largest of the tapeworms - they can grow to be 25 feet or longer. Tapeworms

are made up of hundreds of segments, each of which is capable of breaking off

and developing into a new tapeworm. The infective stage of helminth is either the

adult organism or larvae because the egg constitude the infective stage of the

organisms. The eggs and larvae are very resistant and may survive common

disinfection procedures.

It has been estimated that 25% of the world’s population have been infected with

the round worm nematode Ascaris lumbricoides (Toze, 2004). A number of other

helminthes are developed in certain regions of the world. For example

Strongloides stercoralis a soil transmitted parasitic nematode, is endemic in

northern Australia (Toze, 2004). Strongloides infections are rare in the more

southern regions of the continent. If a wastewater reuse plant is considered in

such a region this parasite must be considered.

Helminth infections are a problem for infants and that chronic infection begins at

a young age. Chronic Helminth infections affect the physical and mental

development of children (Khurro, 1996). Helminth eggs need a period of five to

ten days before they are able to cause infection. In contaminated soil the eggs

can remain infectious for upto ten years (Toze, 2004). This means that soils

which have been in contact with recycled waters contaminated with faecal

material could be considered as long- term sources of these parasites (Ellis et al.,

1993; WHO, 1989). Helminths can be removed by sedimentation, filtration, or

stabilization ponds.


3.2 Survival of Pathogens on Food Crops

Levels of viruses, parasites, reported in untreated and secondary treated

effluents are shown in Tables 3-3 and 3-4. These Tables illustrate the

tremendous range in the concentrations of microorganisms that may be found in

raw and secondary wastewater.

The transmission of foodborne illness by enteric pathogens due to irrigation with

reclaimed water is well known. For that reason the irrigation of food crops

especially those that are eaten raw is usually forbidden. Crops that are eaten raw

should be irrigated with reclaimed water that meets the same standards for

reclaimed water intended for potable reuse. Lower quality of water is used for the

irrigation of orchard crops such as citrus and other fruits. Also for apples and

raspberries a water of high microbial quality should be used. Foodborne illness

are connected with enteric microorganisms are present during the mishandling of

food when an ill food handler does not practice proper sanitation (for example the

hand washing).

Table 3-3: Microorganism Concentrations in Raw Wastewater Organism Range in Average Concentrations

(CFU*,PFU** or Cysts/Oocysts)Faecal Coliforms/100L 105 to 105

Enterococi/100L 104 to 105

Shigella/100mL 1 to 103

Salmonella/100 mL 102 to 104

Helminth ova/100mL 1 to 103

Enteric virus/100L 1 to 5x 103

Giardia cysts/100L 0.39 to 4.9 x104

Cryptosporidium oocysts/100L 0.2 to 1.5 x 103

*CFU – Colony forming unit**PFU- Plaque forming unit

Source: EPA, 2004

Table 3-3 shows the microorganism concentrations in raw wastewater and Table

3-4 shows the microorganism concentrations in secondary non-disinfected

wastewater. Virus of hepatitis A has been trace in crops because of

contamination with the field (for example imported lettuce and raspberries). If the


crop is used for animal feed or grazing there is a chance for transmission of

enteric pathogens that infect both humans and animals.

Table 3-4: Microorganisms Concentrations in Secondary Non-Disinfected Wastewater Organism Average Concetrations

(CFU,PFU or Cysts/Oocysts per 100L)Faecal Coliforms/100L 7,764Enterococi 2,186Enteric virus 20 to 650Giardia cysts 5 to 2,297Cryptosporidium oocysts 140Source: EPA, 2004

The critical factors for the survival of pathogens on crop are:

Temperature

Moisture

Exposure to sunlight

pH

The relationship that exists between temperature and survival of enteric

pathogens one could say that it is inversely proportional; i.e. the lower the

temperature, the longer the survival enteric pathogens. Temperature is probably

the most important factor influencing virus inactivation in the environment (Bitton,

1980) and it also affects the persistence of viruses in soils. As a general rule in

the field most enteric pathogens survive for a shorter period of time on crops than

in the soil (Feachem et al., 1983). Also contamination of crop from the soil can

happen when the crop grows. Although field temperatures during the growing

season often exceed 200C during the day, and many crops are stored post-

harvest at temperatures between 4 and 8oC. In this range of temperature is

expected little inactivation of pathogens. The ultraviolet light in sunlight will

inactivate microorganisms by inducing damage to the nucleic acid. Leaves and

other plant surfaces will reduce temperatures, exposure to direct sunlight and

evaporation. Also in rainfall periods will increase the humidity of the air. Crops

can become contaminated by soil anytime during the growing and harvesting of

the crop. Table 3-5: Survival of viral particles and bacteria in soil and groundwater


Factor Virus BacteriaMoisture content

Increased virus reduction in drying soils although reduction rates varies between viral types

Bacteria survive longer in moister soils

Moisture holding capacity

Viral dependant. Some viruses more susceptible to drying

Survival is less in sandy soils with lower water- holding capacity

Soil Type Adsorption to surfaces can increase survival times

Clay coatings can inhibit pedaction and parasitism effects.Adsorption can increase survival times

pH Indirect effects through effects on adsorption. Most enteric viruses stable between pH 3 and 9

Shorter survival times in acidic soils.

Cations Generally increased cations increases virus survival. The opposite has also been observed

Increased cations increases adsorption which tends to increase survival rates

Soluble organics

May protect viral particles from inactivation. Some evidence to suggest may reversibly decrease infectivity

Increased survival and possible regrowth when sufficient amounts of organic matter are present

Temperature Increased temperature decreases virus survival

Lower temperatures increase survival rates

Sunlight Minor influence at the soil surface Bacterial survival is least at the soil surface where the light is most intense

Microbial factors

The presence of indigenous microorganisms has been shown to decrease virus survival times. Survival varies between virus types.

Indigenous microbes tend to out compete introduced microorganisms

Type of organism

Different viruses vary n their ability to with stand environmental conditions

Varies depending on bacterial physiology, metabolism, spore formation, ability to form biofilms etc.

Source: Roper and Marshall 1979; Gerba and Bitton 1984; Yates and Yates 1988

Factors influencing the survival of viruses and bacteria in soil and groundwater

are listed in Table 3-6. Such factors include the environment into which they are

added, treatment type and type of microorganism.

Microorganisms have also been shown to have a wide range of survival times in

soils, on crop surfaces, in fresh water and sewage depending on the

environmental conditions (Feachem et al., 1983). The survival times for selected

pathogenic microorganisms in soil on crop surfaces and in fresh water and

sewage are given in Table 3-6.

Enteric viruses survive more than 2 weeks during a summer growing season and

6 weeks during the fall or spring growing season. They also survive many weeks

after the harvesting period. Larkin et al., (1976) reported that poliovirus survived

on lettuce or radishes for 14 to 36 days after irrigation and had been artificially

contaminated with poliovirus. However the virus concentration decreased 99


percent during the first 4 to 5 days. Survival time was longer for plants grown in

the fall than those grown during the summer. Unlike enteric viruses and

parasites, some enteric bacteria may grow on contaminated fruits and

vegetables. Because of desiccation and exposure to sunlight, helminth eggs

deposited on plant surfaces die off more rapidly than in the soil. Rudolfs et al.

(1950) in their review concluded that Ascaris eggs, the longest lived of the

helminth eggs, sprayed on tomatoes and lettuce, to be completely degenerated

after 27-35 days.

Table 3-6: Typical Pathogen Survival Times at 20-300C Pathogen Fresh Water

&SewageCrops Soil

Virusesa

Enterovirusesb <120 but usually<50 <60 but usually<15 <100 but usually<20BacteriaFecal coliforms a,c <60 but usually<30 <30 but usually<15 <70 but usually<20Salmonella spp.a <60 but usually<30 <30 but usually<15 <70 but usually<20Shigella spp.a <30 but usually<10 <10 but usually<5 -----Vibrio choleraed <30 but usually<10 <5 but usually<2 <20 but usually<10ProtozoaEntamoeba histolytica cysts

<30 but usually<15 <10 but usually<2 <20 but usually<10

HelminthsAscaris lumbricoides eggs

Many months <60 but usually<30 Many months

a In seawater,viral survival is less and bacterial survival is very much less,than in fresh water.b Includes polio-,echo-,and coxsackievirusesc Faecal coliform is not a pathogen but is often used as an indicator organismd V.cholerae survival in aqueous environments is a subject of current uncertainty

Source: Feacham et al., 1983

3.3 Survival of pathogens on non- food crops

Salmonella and other enteric bacteria can survive for several weeks on grass if

sufficient organic matter and moisture is available. Helminth eggs such as

Ascaris are believed that they can survive for 30 to 60 days, although they may

survive for many months in the soil (Feachem et al., 1983).

Overall pathogens can be ranked in the following descending order of risk

(Shuval et al., 1986):


High – Helminths (the intestinal nematodes – ascaris, trichuris, hookworm,

and taeniasis)

Lower – Bacterial Infections (cholera, typhoid, and shigellosis) and Protozoan

infections (amebiasis, giardiases )

Least – Viral Infections (viral gastroenteritis and infectious hepatitis)

3.4 Reduction of Pathogens through Wastewater Treatment

The choice of the right wastewater treatment technologies is the most important

parameter in planning the water reuse because they are the important way of

decreasing or eliminating the environmental risk. The environmental risk is

connected with the contamination that can be found in the upgraded wastewater

and generally risk can be divided into chemical and microbiological. The purpose

of the wastewater treatment is to protect the consumer from pathogens and from

impurities in the water that may be injurious to human health. This can be

achieved with treatments such as coagulation, sedimentation, filtration and

advanced treatments, to remove pathogens.

Processes are grouped together to provide various levels of treatment known as

preliminary, primary, advanced primary, secondary (without or with nutrient

removal), and advanced (or tertiary) treatment (see below Table 3-7). In

preliminary treatment solids such as large objects and grit are removed. In

primary treatment, a physical operation, usually sedimentation is used to remove

the floating and settleable materials found in wastewater. For advanced primary

treatment, chemicals are added to enhance the removal of suspended solids and

to a lesser extent, dissolved solids. In secondary treatment, biological and

chemical processes are used to remove most of the organic matter. In advanced

treatment combinations of processes are used to remove residual suspended

solids and other constituents that are not reduced by secondary treatment

(Metcalf and Eddy, 2003).


The persistence of bacteria, viruses and protozoan is related to the concentration

of successive treatment step (biological treatment, filtration and disinfection) has

the potencial to reduce the concentrations of indicators and pathogens,

depending on the wastewater characteristics, flowrate, operating conditions and

the overall treatment performance. If the treatment system is highly effective, the

concentrations of indicators and pathogens may be below detection limits.

Pathogens that enter a wastewater treatment system may be freely dispersed,

associated with the cells that they infect, or adsorbed to solids. The pathogens

may be removed, inactivated, destroyed, consumed by higher life-forms, or leave

the treatment system.

Pathogens may be removed from the wastewater by their adsorption to biological

solids or inert solids. The biofilm within the sewer system adsorbs and filters out

many pathogens. Some of these such as Leptospira interrogans grow in the

biofilm inside manholes. Many pathogens are removed from the wastewater

when solids on which they are adsorbed settle out in primary clarifiers. Some

pathogens such as protozoan cysts and oocysts and helminth eggs settle out in

large numbers in primary clarifiers because of their relatively high density.

Biological treatment processes such as activated sludge (suspended growth) and

trickling filter remove many pathogens. The pathogens are adsorbed and

entrapped in floc particles in the activated sludge process and biofilm of the

trickling filter process.

Primary sludge contains a large number and diversity of pathogens. Although

removal efficiency for viruses, bacteria, and fungi shows high variation during

primary sedimentation, primary clarifier sludge does contain a significant number

and diversity of viruses, bacteria and fungi. Most of these pathogens are

removed in primary clarifiers through their adsorption to settleable solids.

Table 3-7: Levels of wastewater treatment Treatment level Description


Preliminary Removal of wastewater constituents such as rags, sticks, floatables, grit, and grease that may cause maintenance or operational problems with the treatment operations, processes, and ancillary systems

Primary Removal of a portion of the suspended solids and organic matter from the wastewater

Advanced primary

Enhanced removal of suspended solids and organic matter from the wastewater. Typically accomplished by chemical addition or filtration

Secondary Removal of biodegradable organic matter (in solution or suspension) and suspended solids. Disinfection is also typically included in the definition of convetional secondary treatment

Secondary with nutrient removal

Removal of biodegradable organics, suspended solids, and nutrients (nitrogen, phosphorus, or both nitrogen and phosphorus)

Tertiary Removal of residual suspended solids (after secondary treatment), usually by granular medium filtration or microscreens (sand filtration). Disinfection is also typically a part of tertiary treatment. May achieve nutrient removal especially phosphorus with the addition of chemicals.

Advanced Removal of dissolved and suspended materials remaining after normal biological treatment when required for various water reuse applications

Source: Crites and Tchobanoglous, 1998

Protozoan cysts and oocysts and helminth eggs are removed during primary

sedimentation. Because of their size and density are more easily removed in

primary clarifiers. With increasing detention time in primary clarifiers, cysts,

oocysts, and eggs as well as viruses, bacteria, and fungi are removed in

increasing numbers. Therefore, primary sludge is heavily laden with pathogens.

Secondary sludge also contains a large number and diversity of pathogens.

Secondary sludge contains settled solids in the form of floc particles or biofilm

from biological treatment processes. Because of the large surface of floc particles

and biofilm viruses, bacteria, and fungi are removed easily in large numbers from

the wastewater. Therefore secondary sludge also is heavily laden with

pathogens. Primary and secondary sludges are transferred to aerobic and

anaerobic digesters for additional treatment.

Pathogens may be inactivated or destroyed through biological, chemical and

physical treatments. Inactivation is a period of time during which the pathogen is

rendered harmless or incapable of causing an infection. If the inactivation method

is long enough, the pathogen dies. When the inactivation period is not long

enough, the pathogen may become active and may cause infection.


Pathogens within wastewater treatment systems may be inactivated or destroyed

by exposure to the following biological, chemical, or physical conditions (Geraldi,

2005):

Anaerobic environment

Anoxic environment

Competition for nutrients

Consumption and digestion by higher liofe-forms

Depressed pH (<3)

Desiccation

Disinfection

Elevated pH (>11)

Elevated temperature

Entrapment in biological solids

Presence of Heavy metals

Inability to adapt to a free-living state in the aquatic environment

Inability to find a suitable host

Long retention time in treatment units

Presence of oxidizing agents such as chlorine or ozone

UV light penetration

For the inactivation of pathogens and destruction the following can be said:

Anaerobic digestion of sludge is more effective in inactivating and destroying

pathogens than aerobic digestion of sludge

Disinfection of the effluent inactivates and destroys many but not all

pathogens

Increased pathogen inactivation and destruction occur with increasing

retention time in treatment units or increase dosing of disinfection agent.

3.5 Removal of Parasites through Stabilization Ponds


The above findings, which are supported by the theoretical settling calculations,

suggest that primary sedimentation cannot be relied on for effective removal of

pathogenic protozoans and helminths from wastewater.

Some additional removal may be obtained by conventional biological treatment,

but the reported results are not uniform. Oxidation ponds usually provide

detention periods of 5 to 30 days and should provide better conditions for the

sedimentation of protozoans and helminths than conventional primary

sedimentation plants with detention times of 2 or 3 hours or secondary treatment

systems with total detention of 8 to 12 hours.

Wachs (1961) found that cysts of Entamoeba hystolytica could be effectively

removed from sewage after 20 days' detention in a stabilization pond. Arceivala

(1970) reports that a municipal oxidation pond in India with a total detention

period of 7 days produced an effluent free of protozoan cysts and helminths eggs

despite the heavy load of parasitic cysts and eggs in the influent (from 100 to

1,000 per liter). He concluded that oxidation ponds are more effective in

removing helminths and protozoans than conventional treatment plants and can

provide greater protection to the health of farm workers in contact with sewage

used in agriculture.

3.6 Removal of Parasites by secondary and tertiary treatment

Trickling filters alone do not appear to be efficient in removing protozoal cysts

and helminth eggs. Entamoeba hystolytica removal of 83-99 percent has been

reported. Egg removal appears to be in the range of 20-90 percent, with higher

reductions when the effect of secondary sedimentation is included.

The activated sludge process itself has little effect on protozoal cysts and

helminth eggs, but substantial proportions of eggs will be removed in the

secondary settling tank (activated sludge plants have been reported to remove


80-100 percent of helminth eggs). Overall, the results that have been obtained

with conventional treatment vary.

Vassilkova (1936) reported that treatment in an Imhoff tank removed 97 percent

of all helminth eggs present in the influent examined, and a trickling filter

removed 87 percent. Roberts (1935) reported the Cysticecus bovis infection of 23

of 45 cattle grazed on a sewage farm irrigated with primary effluent. Cram (1943)

reported that after primary sedimentation, effluent from activated sludge and

trickling filters contained significant numbers of hookworm and ascaris eggs,

which were completely removed only after chemical coagulation with alum and

sand filtration. In addition, a study of five plants in Johannesburg found tapeworm

eggs in both raw and settled sewage and in the effluent of trickling filter and

activated sludge plants (Hamlin 1946), and still others (Silverman and Griffiths

1955) have also concluded that conventional primary sedimentation, even when

followed by secondary treatment, cannot be relied on to effectively remove

tapeworm eggs from sewage.

At the same time, Kott and Kott (1967) report a 50 percent reduction in E.

histolytica cysts after primary sedimentation and trickling filter treatment and a 90

percent reduction in the final effluent. Rowan (1964) reports from a study of eight

sewage treatment plants in Puerto Rico that primary treatment removed 35 to 74

percent of the ascaris and 83 percent of the schistosome eggs; trickling filters

and activated sludge treatment removed 95 to 99.7 percent of the ascaris and

schistosome eggs. In most cases, schistosome eggs hatched during treatment

and allowed large numbers of infective miracidia to escape into the stream, the

effluent serving as a potential source for dissemination of the disease.

Postchlorination or other tertiary treatment was considered essential to prevent

further schistosome infections.

Even though tertiary treatment processes (sand filtration; membrane separations;

granulated carbon adsorption; powdered activated carbon; ion exchange) are

used for further reduction of suspended solids rather than pathogen removal,


some of them do have good pathogen-removal characteristics. Coagulation could

achieve some pathogen removal. Slow sand filters is effective in removing

protozoa, helmith eggs and viruses, and are highly recommended where there is

a lack of trained operators and land is available. Land treatment by percolation

may have similar results if properly designed and operated, and if groundwater

contamination is not expected.

Maturation lagoons receiving effluents from aerobic ponds will remove parasites

on the same principle as of waste stabilization ponds. If two or more maturation

ponds are used, with perhaps 5 days of retention in each, high removal of

protozoan cysts and helminth eggs can be achieved. Effluent chlorination is not

efficient in eliminating protozoan cysts because they are more resistant than

either excreted viruses or bacteria. Most helminth eggs are totally unharmed by

effluent chlorination.

3.6.1 Removal of Pathogens by Primary Sedimentation

Preliminary treatment by screening will have no effect on the pathogen content of

wastewater. In primary settling tanks with 2 or 3 hours of detention, parasites

may be removed either by direct sedimentation or by being absorbed onto solids

that are in the process of settling. Sedimentation tanks have Entamoeba

histolytica cysts are generally reduced by 50 percent or less, while 50-70 percent

of helminth eggs (Feachem et al., 1983) usually settle.

Bhaskaran et al. (1956) reported only 50 percent removal of helminth eggs in a

number of primary sedimentation plants in India and about 70 percent removal of

Ascaris and hookworm eggs by a septic tank. Phadke et al., (1972) reported

considerable reductions of ascaris and hookworm eggs in a septic tank effluent

with 20 days' detention, but positive helminth cultures were obtained for the

majority of effluent samples tested.

Liebman (1965) contends that, although the larger helminths with a specific

gravity greater than 1.1 should theoretically be effectively removed in primary


sedimentation tanks, variation in detention times, the presence of detergents,

and other circumstances leading to nonuniform sedimentation conditions may

cause a relatively low removal efficiency, with the result that pathogenic

helminths may still be disseminated by sewage effluent used to irrigate fields. In

his opinion, biological treatment provides little additional removal capability. He

recommends chemical coagulation for more effective removal.

3.6.2 Filtration

Filtration is a common treatment process used to remove particulate matter prior

to disinfection. Filtration involves the passing of wastewater through a bed of

granular media or filter cloth, which retain the solids. Typical media include sand,

anthracite, and garnet. Removal efficiencies can be improved through the

addition of certain polymers and coagulants. Filtration can achieve log 2 order of

magnitudes for bacteria e.g. from 105 - 103.

The addition of coagulant can increase the removal of poliovirus to 99 %

(USEPA, 1992). Removals of 90% or greater can be achieved, the more enteric

viruses inactivate. Reverse osmosis and ultrafiltration can achieve more

reduction of enteric pathogens. Nanofiltration also achieves 99% reduction of

MS2 coliphage (Yahya, 1994).

3.7 Advanced Wastewater treatment

Advanced wastewater treatment, sometimes referred to as tertiary treatment, and

is generally defined as anything beyond secondary treatment. These methods

are applied when a high quality of reclaimed water is required such as for the

irrigation of urban landscaping and food crops that are eaten raw.

Tertiary or advanced treatment systems are used to improve the physico-

chemical quality of biological secondary effluents. Several unit operations and

unit processes, such as coagulation-flocculation-settling-sand filtration,

nitrification and denitrification, carbon adsorption, ion exchange and electro-

dialysis, can be added to follow secondary treatment in order to obtain high


quality effluents. None of these units are recommended for use in developing

countries when treating wastewater for reuse, due to the high capital and

operational costs involved and the need for highly skilled personnel for operation

and maintenance.

If the objective is to improve effluents of biological plants (particularly in terms of

bacteria and helminths), for the irrigation of crops or for aquaculture, a more

appropriate option is to add one or two ponds as a tertiary treatment. If land is

not available for that purpose, horizontal or vertical-flow roughing filtration units

(which have been used for pre-treatment of turbid waters prior to slow-sand

filtration) may be considered. These units, which are low cost and occupy a

relatively small area, have been shown to be very effective for the treatment of

secondary effluents and remove a considerable proportion of intestinal

nematodes.

3.7.1 Reduction of Pathogens through Disinfection Processes

The most important process of destruction of microorganisms is disinfection. The

main disinfectants used in the removal of pathogens from wastewater are

chlorine (Cl2) and ozone (O3). Other disinfectants that can be used are chlorine

dioxide (ClO2) and chlorine-separating substances such as chlorinated lime (a

mixture of CaO and CaOCl) and sodium hypochloride (NaOCl).

To disinfect all wastewater treatment plant outflows has so far been rejected in

many European countries for the following reasons:

Other discharges of wastewater containing pathogens, such as mixed

discharges from the sewer system or diffuse discharges from municipal or

agricultural sources, are not covered.

Drinking water is mainly recovered from groundwater (for example: Denmark:

99%, Italy 87%, Germany 73%, France 64%, Great Britain 28%, USA 10%)

The advantages of wastewater disinfection do not justify the cost, because

humans rarely come into direct contact with raw sewage, treated wastewater

or highly contaminated bodies of water.


Chlorination of wastewater treatment plant outflows can cause considerable

harm to the water biocoenosis and in addition lead to the unwanted formation

of organic chlorine compounds.

Disinfection is accomplished with the use of (1) chemical agents, (2) physical

agents and (3) radiation.

3.7.1.1 Chemical agents Chemical agents that have been used as disinfectants are: (1) chlorine and its

compounds, (2) bromine, (3) iodine, (4) ozone, (5) phenol and phenolic

compounds, (6) alcohols, (7) heavy metals, (8) soaps and synthetic detergents,

(9) hydrogen peroxide, (10) various alkalies, (11) various acids. From the above

disinfectants the most common are the oxidising chemicals and chlorine is very

popular.

3.7.1.2 Physical agents Physical disinfectants that may be used are heat, light, and sound waves. Heat is

used in the beverage and dairy industry, but it is not possible to disinfect large

quantities of wastewater because of the high cost. Sunlight is a very good

disinfectant, due to UV (ultraviolet) radiation.

3.7.1.3 Radiation The types of radiation such as electromagnetic, acoustic and particle are

important. Gamma rays because of their penetration power have been used to

disinfect both water and wastewater, (Metcalf and Eddy, 2003). A disinfectant

agent must have certain characteristics which can see in the below Table 3-8.

Table 3-8: Characteristics of an ideal disinfectant Characteristic Properties/responseAvailability Should be available in large qualtities and reasonably pricedDeodorizing ability Should deodorize while disinfectingHomogeneity Solution must be uniform in compositionInteraction with extraneous material

Should not be adsorbed by organic matter other than bacteria cells

Noncorrosive and nonstaining

Should not disfigure metals or stain clothing


Nontoxic to higher forms of life

Should be toxic to microorganisms and non-toxic to humans and other animals

Penetration Should have the capacity to penetrate through surfacesSafety Should be safe to transport, store, handle, and useSolubility Must be soluble in water or cell tissueStability Should have low loss of germicidal action with time on standingToxicity to microorganisms Should be effective at high dilutionsToxicity at ambient temperatures

Should be effective in ambient temperature range

Source: Metcalf and Eddy, 2003

3.7.2 Disinfection with chlorine

The common disinfectant is chlorine (for both water and wastewater). Disinfection

with chlorine depends from water temperature, pH, and degree of mixing, time or

contact presense of substances, concentration form of species. Bacteria are less

resistant to chlorine than are viruses and which are less resistant than parasite

ova and cysts.The dosage of chlorine that is required to disinfect a wastewater

depends from the constituents present in wastewater. Chlorine in low

concentrations is very toxic to aquatic organisms and in reclaimed water is

controlled by dechlorination with sulfur dioxide. Dechlorination is used to

minimize these effects.

Disinfection of wastewater through the application of chlorine has never been

completely successful in practice for untrated wastewater, due to the high costs

involved and the difficulty of maintaining an adequate, uniform and predictable

level of disinfection efficiency. However, this is not true for treated wastewater.

Effluents from well-operated conventional treatment systems, treated with 10-30

mg l-1 of chlorine and a contact time of 30-60 minutes, provide a good reduction

of excreted bacteria, but have no capacity for removing helminth eggs and

protozoan. A well designed and operating stabilisation ponding system can

provide an effluent with less than 1,000 faecal coliform per 100 ml and less than

one egg of intestinal nematodes per litre. This however is not the reason that

disinfection is not applied after stabilisation ponds: disinfection with chlorine,

ozone or even UV is difficult for effluent of stabilisation ponds due to the high

content of suspended solids and BOD.


Even though chlorination is effective in killing bacteria and inactivating enteric

viruses, these pathogens can be protected in suspended and colloidal solids if

the wastewater has not been filtered first for turbidity (solids) removal; that is

where the need arises for tertiary treatment. Cysts of protozoan and helminth

eggs are resistant to chlorine, and they need to be physically removed by

effective chemical coagulation and granular-media or membrane filtration. For

reasons of cost, wastewater chlorination has so far been considered to be the

disinfection procedure of choice in almost all instances.

3.7.3 Disinfection with Ozone (O3)

It is a powerful disinfecting agent and chemical oxidant in both inorganic and

organic reactions. Due to the instability of ozone, it must be generated onsite

from air or oxygen carrier gas. Ozone destroys bacteria and viruses by means of

rapid oxidation of the protein mass, and disinfection is achieved in a matter of

minutes. Ozone is a highly effective disinfectant for advanced wastewater

treatment plant effluent, removing colour, and contributing dissolved oxygen.

Ozone destroys bacteria and viruses. Is very effective in advanced wastewater

treatment and removes colour, and contributes dissolved oxygen.

Some disadvantages to using ozone for disinfection are (Metcalf and Eddy, 2003:

The use of ozone is relatively expensive and energy intensive,

Ozone systems are more complex to operate and maintain than chlorine

systems,

Ozone does not maintain a residual in water.

It requires high quality effluent in order to be more effective

In comparison with chlorination, disinfection with ozone is better for the receiving

bodies of water. Ozone is highly reactive gas and cannot be stored or

transported over long distances. Ozone is also used for the disinfection of treated

wastewaters. Factors that should be considered are effectiveness and reliability,

capital and operating, maintenance costs effects (such as toxicity) to aquatic life


or formation of these toxics. Very important factor to consider is the need to have

a continuous high quality treated wastewater with very low suspended solids.

3.7.4 Disinfection with UV radiation

UV radiation is frequently used for wastewater treatment plants that discharge to

surface waters to avoid the need for dechlorination prior to release of the effluent.

UV is receiving increasing attention as a means of disinfecting reclaimed water

for the following reasons:

UV may be less expensive than disinfecting with chlorine,

UV is safer to use than chlorine gas,

UV does not result in the formation of chlorinated hydrocarbons, and

UV is effective against Cryptosporidium and Giardia, while chlorine is not.

The effectiveness of UV radiation as a disinfectant (where fecal coliform limits are

on the order of 200/100 ml) has been well established, and is used at small- to

medium-sized wastewater treatment plants throughout the U.S (Metcalf and

Eddy, 2003). A comparison between of disinfection treatments is given below

(Table 3-9).

Table 3-9: Comparison of different disinfection treatmentsCharacteristics/Criteria

Chlorination/Dechlorination

UV Ozone Micro-filtration

Ultra- filtration

Nano-filtration

Safety low high middle high high highBacterial removal

middle middle middle middle high high

Virus removal low low middle low high highProtozoa removal

none none middle high high high

Bacterial regrowth

low low low none none none

Residual toxicity high none low none none noneBy- products high none low none none noneOperating costs low low middle high high highInvestment costs middle middle high high high highSource: Urkiaga and Fuentes, 2004

The combination of chorination/dechlorination, corresponds to large doses of

chlorine, and is more effective than simple chlorination due to the destruction of

pathogenic bacteria and viruses at doses of 30-50 mg/l. However, chlorination


requires far smaller doses of chlorine. The result is that after a retention time of

30-60 minutes in the contact tank, the residual chlorine is of the value of 1-2 mg/l.

This concentration does not need dechlorination.

Today, UV radiation to achieve high-level disinfection for reuse operations is

acceptable in some states and is less expensive from chlorine disinfection. It is

safer to use than chlorine gas.

In general when a decision has been taken to remove pathogens from

wastewater using disinfection, the following points must be considered:

Mechanical-biological wastewater treatment should be arranged upstream of

the disinfection stage.

UV irradiation should be preffered to methods employing the use of

chemicals. However UV irradiation requires water that is free from turbid

matter to a large extent to allow the radiation to take optimum effect.

Other methods that can possibly be applied include the use of ozone, chlorine

dioxide, hydrogen peroxide.

If possible, the number of pathogens at the treatment plant outflow should be

below the guide values of the EU guidelines for bathing water (Table 3-6).

A summary of various treatments and processes that bacteria can be removed

are shown in Table 3-10.

Table 3-10: Removal or destruction of bacteria by different treatment processes Process Percent removalCoarse screens 0-5Fine screens 10-20Grit chambers 10-25Plain sedimentation 25-75Chemical precipitation 40-80Trickling filters 90-95Activated sludge 90-98Chlorination of treated wastewater 98-99.999Source: Metcalf and Eddy, 2003


Aerated lagoons, ponds with mechanical aerators have been reported to provide

removal rates of 60-99.99 percent for total coliforms and 99 percent for faecal

coliforms, total bacteria, Salmonella typhi, and Pseudomonas aeruginosa (Crites

and Uiga, 1979).

The performance of pond system is not reliable since it depends on the weather

conditions and on the eutrophication which may be experienced in sunny

climates. The Cyrpus experience showed that under operating conditiond (and

not under experimental conditions) for a series of ponds with total retention time

of more than 25 days (anaerobic-fucultative-maturation) the coliform counts were

at the order of 103-104.

Pond effluents contain high suspended solids and can not be distributed to

advance irrigation systems. There will be clogging problems to sprinklers to drop

irrigation systems etc. So in countries where guidelines specify advanced

irrigation methods it may not be advisable to adapt ponds as a system of

treatment. Experience showed that institution of mechanical filtration of pond

effluent also created problem of clogging of the filters.

Thus, wastewater stabilization ponds can be designed to achieve practically any

degree of bacterial pathogen removal deemed necessary for the protection of

public health, including complete wastewater treatment. Such a high degree of

removal is not necessary for most land application systems (Kowal et al., 1981).

From the point of view of environmental health, the minimum demands on the

treatment plants should be set in the following order of priority:

Priority 1: Highly effective removal of helminths (100 percent).

Priority 2: Reasonably effective removal of bacteria (minimum 99-99.9

percent) and some removal of viruses.

Priority 3: Proper loading and dissipation of BOD to eliminate odor.

Effluents should meet appropriate water quality and other environmental criteria.

These will vary both between and within countries and within cities. Without


exception, standards for developed countries are inappropriate. On the basis of

the above data, it is recommended that plants use the following layout:

Anaerobic ponds, at least two in parallel, with a minimum of 2 days' total

detention time. This will partly take care of both the helminth problem and

BOD (without environmental nuisance, if properly operated)

Facultative pond(s), usually 5-10-15 days' total detention time (depending on

ambient temperature) to remove BOD, to reduce bacteria by one to two

orders of magnitude, and to serve as a safety factor for helminth eggs carried

over from the anaerobic pond(s).

Maturation pond(s) in series, as necessary, to achieve reasonably high

bacterial removal. A standard unit for maturation ponds for each location is

highly recommended, ideally, a detention time of 5 days each.

Table 3-11 shows the removal of pathogens with different treatment processes

Table 3-11: Expected removal of excreted organisms in various wastewater treatment processes. Values are expressed as log10 units 4 log10 units (i.e.equivalent to = 10-4 = 99.9 percent removal)

Treatment process Bacteria Helminths Viruses Cysts

Primary sedimentation (plain) 0-1 0-2 0-1 0-1Primary sedimentation (chemically)a 1-2 1-3 g 0-1 0-1Activated sludge b 0-2 0-2 0-1 0-1Biofiltration c 0-2 0-2 0-1 0-1Aerated lagoon c 1-2 1-3 g 1-2 0-1Oxidation ditch b 1-2 0-2 1-2 0-1Disinfection d 2-6 g 0-1 0-4 0-3Waste stabilization ponds e 1-6 g 1-3 g 1-4 1-4Effluent storage reservoirs f 1-6 h 1-3 h 1-4 1-4a Further research is needed to confirm performance.b Including secondary sedimentation.c Including settling pond.d Chlorination or ozonation.e Performance depends on number of ponds in series and other environmental factors.f Performance depends on retention time, which varies with demand.g With good design and proper operation the recommended guidelines are achievable.

Source: Mara and Cairncross, 1989


4. Groups of population at risk and epidemiological evidence of human health effects associated with wastewater irrigation

4.1 Groups of population at risk.

Four groups of the population are at risk during agricultural wastewater reuse.

These are:

agricultural field workers and their families

crop handlers

consumers of crops, meat and milk

people living near the areas irrigated with wastewater

and different methods of exposure control might be applied for each group.

4.2 Human Health effects associated with wastewater irrigation

WHO guidelines (WHO, 1989) were based on a number of available

epidemiological studies, many of which were reviewed by Shuval et al. (1986).

The evidence at that time suggested that the use of untreated wastewater in

agriculture presented a high actual risk of transmitting intestinal nematodes and

bacterial infections especially to produce consumers and farm workers; but that

there was limited evidence and the health of people living near wastewater-

irrigated fields was affected. There was less evidence for the transmission of

viruses and no evidence for the transmission of parasitic protozoa to farm

workers, consumers or nearby communities. The review of epidemiological

evidence by Shuval et al. (1986) also indicated that irrigation with treated

wastewater did not lead to excess intestinal nematode infections among field

workers or consumers (WHO, 1989).

In 2002, Blumenthal and Peasey completed a critical review of epidemiological

evidence on the health effects of wastewater and excreta use in agriculture for

WHO. A sub-set of analytical epidemiological studies were selected that included

the following features: well-defined exposure and disease, risk estimates

calculated after allowance for confounding factors, statistical testing of


associations between exposure and disease, and evidence of causality (where

available). These were used as a basis for estimating threshold levels below

which no excess infection in the exposed population could be expected. Further

information on the risks of infection attributable to exposure, and in particular on

the proportion of disease in the study population attributable to exposure (and

therefore potentially preventable through improvement in wastewater quality),

was used to inform proposals on appropriate microbiological guidelines for

wastewater reuse in agriculture. A summary of the results of this epidemiological

review are presented in Table 4-1.

Table 4-1: Summary of health risks associated with the use of wastewater in irrigation. Group exposed

Nematode infection Bacterial/Viruses Protozoa

Consumers Significant risks of Ascaris infection for both adults and children with untreated wastewater; no excess risk when wastewater treatyed to <1 nematode egg/l except where conditions favour survival of eggs

Cholera, typhoid and shigellosis outbreaks reported from use of untreated wastewater, sero-positive responses for Helicobacter pylort (untreated); Increase in non-specific diarrhoea when water quality exceeds 104FC/100ml

Evidence of patasitic protozoa found on wastewater. Irrigated vegetable surfaces but no direct evidence of disease transmission

Farm workers and their families

Significant risks of Ascaris infection for both adults and children with contact with untreated wastewater, risks remain, especially for children when wastewater treated to <1 nematode egg/l.Increased risk of hookworm infection to workers

Increased risk of diarrhoeal disease in young children with wastewater contact if water quality exceeds 104 FC/100ml: elevated risl of salmonella infection in children exposed to untreated water, elevated seroresponse to Norovirus in adults exposed to partially treated wastewater

Risk of Giardia Intestinallis infection was significant for contact with both untreated and treated wastewater, Increased risk of amoebiasis observed from contact with untreated wastewater

Nearby communities

Ascaris transmission not studied for sprinkler irrigation but same as above for flood or furrow irrigation with heavy contact

Sprinkler irrigation with poor quality water 104 TC/100ml, and high aerosol exposure associated with increased rates of viral infection; use of partially treated water 104 FC/100ml or less in sprinkler irrigation not associated with increased viral infection

No data for transmission of protozoan infections during sprinkler irrigation with wastewater

Source: Blumental et al., 2000a; Armon et al. 2002; Blumental and Peasey, 2002


Wastewater is often a resource for the poor and in many cases the water and

nutrients it contains can have important – yet largely uncharacterised – impacts

on food security (Buechler and Devi, 2003). Improving nutrition, especially for

children, is very important in maintaining the overall health of individuals and

communities. Malnutrition is estimated to have a significant role in the deaths of

50% of all children in developing countries – 10.4 million children under the age

of 5 die each year (Rice et al., 2000; WHO, 2000). Malnutrition affects

approximately 800 million people, or 20% of all people in the developing world

(WHO, 2000). Malnutrition may also have long-term effects on the health and

social development of a community, and leads to both stunted physical growth

and impaired cognitive development (Berkman et al., 2002).

In Table 4-2 estimation risks from the use of untreated or treated wastewater in

irrigation of viral infection per person per year for various concentrations of E. coli

Table 4-2: Estimated risks from the use of untreated or treated wastewater in irrigation of viral infection per person per year for various concentrations of E. coliaE. coli concentration/100 ml Risk of viral infectionb Reference107 (i.e. untreated) 0.2–0.6 (I) CV Fattal and Shuval, 19991000 2–9 × 10-5 (I) CV Shuval et al., 1997≤2.2c 1 × 10-7 – 7 × 10-9 (I) CV Tanaka et al., 1998≤2.2d 2 × 10-8 – 4 × 10-10 (I) WC Tanaka et al., 1998

aE. coli concentrations in wastewater do not necessarily correspond to viral concentrations in wastewater.bRisks are based on either the consumption of irrigated raw vegetables (CV) or contact with the wastewater during/after irrigation (WC).cTotal coliforms in chlorinated secondary effluent used for unrestricted crop irrigation.dTotal coliforms in chlorinated tertiary effluent used for golf course irrigation.

4.3 Effects of use of untreated wastewater

4.3.1 Effects on farm workers or wastewater treatment plant workers

Use of untreated wastewater for crop irrigation causes significant excess

infection with intestinal nematodes in farm workers, in areas where such

infections are endemic. In India, sewage farm workers have a significant excess

of Ascaris and hookworm infections, compared with farm workers irrigating with

clean water (Krishnamoorthi et al., 1973). The intensity of the infections (number

of worms per person) and the effects of infection were also higher, e.g. the

sewage farm workers suffered more from anaemia, one of the symptoms of


severe hookworm infection. There is some evidence that sewer workers may be

at increased risk of protozoan infections such as amoebiasis and giardiasis

(Dolby et al., 1980; Knobloch et al., 1983) but other studies have not found such

an effect (WHO, 2001). There is no reliable data on the impact on amoebiasis on

farm workers in contact with untreated wastewater.

Cholera can be transmitted to farm workers if they irrigate with raw wastewater

coming from an urban area where a cholera epidemic is occurring. This was the

case in the outbreak of cholera in Jerusalem in 1970, where cholera is not

normally endemic and the level of immunity to cholera was low (Fattal et al.,

1986).

There is limited evidence of increased bacterial and viral infections among

wastewater irrigation workers or wastewater treatment plant workers exposed to

untreated wastewater or wastewater aerosols. Sewage treatment plant workers

from three cities in the USA did not have excess gastrointestinal illness but

inexperienced workers had more gastrointestinal symptoms than experienced

workers or controls (municipal workers); however, these were mild and transitory,

and there was no consistent evidence of increased parasitic, bacterial or viral

infections from stool examinations or antibody surveys (WHO, 2001). In a follow

up study, there were no excess seroconversions to Norwalk virus or rotavirus in

the inexperienced workers with gastroenteritis, but inexperienced workers had

higher rates of antibody to Norwalk virus (WHO, 2001).

4.3.2 Effects on consumers of vegetable crops

Irrigation of edible crops with untreated wastewater can result in the transmission

of intestinal nematode infections and bacterial infections. The transmission of

Ascaris and Trichuris infections through consumption of wastewater irrigated

salad crops has been demonstrated in Egypt (Khalil, 1931) and Jerusalem (Fattal

et al., 1986), where the infections fell to very low levels when wastewater

irrigation was stopped.


Transmission of cholera can occur to consumers of vegetable crops irrigated with

untreated wastewater, as during the outbreak of cholera in Jerusalem in 1970. It

appears that typhoid can also be transmitted through this route, as seen in

Santiago, Chile, where the excess of typhoid fever in Santiago compared with the

rest of Chile, and in the summer irrigation months, has been attributed to

irrigation with river water containing untreated wastewater (Ferrecio et al., 1984,

Shuval et al., 1986). In both cases, transmission has occurred in communities

with relatively high sanitation levels where transmission through common routes

such as contaminated drinking water and poor personal hygiene has been

diminished substantially.

Cattle grazing on pasture irrigated with raw wastewater can become heavily

infected with the larval stage of the tapeworm Taenia saginata (Cysticercus

bovis), as has occurred in Australia. There is no epidemiological evidence of

human infection through the consumption of raw or undercooked meat from such

cattle, but the risk of infection through this route probably exists.

Many outbreaks of enteric infection have been associated with wastewater

contaminated foods, but of the very few which were associated with wastewater

irrigation, untreated wastewater was used in all but two cases (Bryan, 1977).

4.4 Effects of use of treated wastewater

4.4.1 Effects on farm workers or nearby populations

There is very limited risk of infection among workers using partially treated

wastewater for irrigation. At Muskegon, USA, workers exposed to partially treated

wastewater (from aeration basins and storage lagoons) had no increase in

clinical illness or infection with enteroviruses. Only highly exposed workers

(nozzle cleaners) had excess antibodies to one enterovirus but no

seroconversion and no excess in clinical illness (Linneman et al., 1984).


Sprinkler irrigation with partially treated wastewater can create aerosols

containing small numbers of excreted viruses and bacteria but there is no

conclusive evidence of disease transmission through this route. Several studies

in Kibbutzim in Israel have addressed this question.

The first study (Katzenelson et al., 1976) suggested increases in salmonellosis,

shigellosis, 14 typhoid fever and infectious hepatitis in farmers and their families

working on or living near fields sprinkler irrigated with effluent from oxidation

ponds (retention 5-7 days), but the study was methodologically flawed. The

second study (Fattal et al., 1986b) found a twofold excess risk of clinical ’enteric’

disease in young children (0-4 years) living within 600-1000m from sprinkler

irrigated fields, but this was in the summer irrigation months only, with no excess

illness found on an annual basis. The third study (Fattal et al., 1986c and Shuval

et al., 1989) found that episodes of enteric disease were similar in Kibbutzim

most exposed to treated wastewater aerosols (sprinkler irrigation within 300-

600m of residential areas) and those not exposed to wastewater in any form. The

wastewater was partially treated in ponds with 5-10 days retention reaching a

quality of 104-105 coliforms/100ml.

No excess of enteric disease was seen in wastewater contact workers or their

families, as well as in the general population living near the fields. This

prospective study is considered to be conclusive, having a superior

epidemiological design.

However, it does seem that transmission of enteric viral pathogens to populations

living near fields sprinkler irrigated with partially treated wastewater can occur

under some circumstances, though this may not result in significant excess

clinical infection. In a seroepidemiological study associated with the third Israeli

study (Fattal et al., 1986c and Shuval et al., 1989) the results suggested that a

non-endemic strain of ECHO 4 virus, which was causing a national epidemic in

urban areas, was transmitted to rural communities through aerosols produced by

sprinkler irrigated of wastewater, though no excess clinical disease was detected


(Fattal et al., 1986). The fact that no similar excess of the other viral antibodies

studied was found suggests that exposure to wastewater aerosols does not lead

to an excess in enteroviral infection under non-epidemic conditions.

4.4.2 Effects on consumers of vegetable crops

When vegetables are irrigated with treated wastewater rather than raw

wastewater, there is some evidence from Germany that transmission of Ascaris

infection is drastically reduced. In Berlin in 1949, where wastewater was treated

using sedimentation and biological oxidation prior to irrigation, rates of Ascaris

infection were very low, whereas in Darmstadt where untreated wastewater was

used to irrigate vegetable and salad crops, the majority of the population was

infected (Baumhogger,1949 and Krey,1949). Rates were highest in the suburb

where wastewater irrigation was practiced, suggesting farm workers and their

families were infected more through direct contact than consumption.

4.5 Exposure to raw wastewater

Farm workers and their children in contact with raw wastewater through irrigation

or play have a significantly higher prevalence of Ascaris infection than those in a

control group, who practice rain-fed agriculture. The excess infection is greater in

children than in adults (Blumenthal et al., 1996, Peasey, 2000). Young children

(aged 1-4 yrs) also have a significantly higher rate of diarrhoeal disease

(Cifuentes et al, 1993).

4.6 Exposure to partially treated wastewater

Contact with wastewater which has been retained in one reservoir before use (<1

Nematode egg/l and 105 FC/100ml) results in excess Ascaris infection in

children, but not in adults, where the prevalence was reduced to a similar level to

the control group (Blumenthal et al., 1996). Children aged 5-14 years also have

significantly higher rates of diarrhoeal disease (Cifuentes et al., 1993, Blumenthal

et al., 2000).


4.7 Risks to consumers related to unrestricted irrigation

Risks from bacterial and viral infections related to the consumption of specific

vegetables (ie. courgette, cauliflower, cabbage, carrots, green tomato, red

tomato, onion, chilli, lettuce, radish, cucumber and coriander) and to total

consumption of raw vegetables irrigated with partially treated wastewater

(average quality 104 FC/100ml) were investigated. Consumers (of all ages) had

no excess infection with diarrhoeal disease, and no excess infection as

measured by serological response to Human Norwalk-like Virus/ Mexico

(Hu/NLV/Mx), or Enterotoxigenic Escherichia coli (ETEC) related to their total

consumption of raw vegetables, that is, the number of raw vegetables eaten each

week (Blumenthal et al., 1998, Blumenthal et al., 2000b).

However, there was an excess of diarrhoeal disease in those in the exposed

area who ate increased amounts of onion compared with those who ate very

little. The effect was seen particularly in adults and children under 5 years of age.

There were also higher levels of serological response in school-aged children

who ate green tomato and in adults who ate salsa (containing green tomato). The

increase in diarrhoeal disease associated with eating increased amounts of raw

chillies was not related to use of partially-treated wastewater as the chillies eaten

by the study population were grown in raw wastewater. Only the risks from eating

onion and green tomato can be associated with using partially treated

wastewater in irrigation. In the final analysis, consumption of onion, or green

tomato, once a week or more was associated with at least a two-fold increase in

diarrhoea. Enteroviruses were found on onions at harvest, giving support to this

epidemiological evidence. The effects described were seen after allowance was

made for other risk factors for diarrhoeal disease. No excess serological

response to enterotoxigenic E. coli was related to raw vegetable consumption.

Consumption of vegetable crops irrigated with water of quality 104 FC/100ml

therefore causes a significant risk of enteric infection in consumers.


4.8 Effects on farm workers or wastewater treatment plant workers

There was no clear association between self-reported clinical illness episodes

and exposure to wastewater (Camann et al., 1986). However, in the data on

seroconversion to viral infections, a high degree of aerosol exposure was related

to a slightly higher rate of viral infections (risk ratio of 1.5-1.8). A dose-response

relationship was observed over the four irrigation seasons; the episodes of viral

infection associated with wastewater exposure mainly occurred in the first year,

before the reservoirs had come into use. More supporting evidence was found for

the role of the wastewater aerosol route of exposure than for direct contact with

wastewater. Of the many infection episodes observed, few were conclusively

associated with wastewater exposure and none resulted in serious illness.

Analysis of clinical viral infection data (from faecal specimens) also showed that

aerosol exposure (high) was associated with new viral infections in the summer

of the first year of irrigation, but the effect was of borderline significance (Camann

and Moore, 1987). However, when allowance was made for alternative risk

factors, eating at local restaurants was identified as an alternative explanation for

the viral infection episodes. In a specific study of rotavirus infection, wastewater

spray irrigation had no detectable effect on the incidence of infection (Ward et al,

1989). Altogether, the results do suggest that aerosol exposure to wastewater of

quality 103-104 FC/100ml does not result in excess infection with enteric viruses.

There is some evidence that exposure to wastewater of quality 106 FC/100ml

results in excess viral infection (but not disease) but this is not conclusive.

A new study of wastewater treatment plant workers (Khuder et al., 1998)

suggests that they have a significantly higher prevalence of gastroenteritis and

gastrointestinal symptoms. There was no association between extent of exposure

and prevalence of symptoms. However, these results are not reliable since

workers were asked about symptoms over the previous 12 months

(retrospectively).


4.9 Effects on consumers of vegetable crops

No epidemiological studies have been located which assess the risk of enteric

infections to consumers of vegetable crops irrigated with treated wastewater.

4.10 Evidence from microbiological studies of crops irrigated with treated wastewater

Work in Portugal during 1985 - 1989 (Vaz da Costa Vargas et al., 1996) explored

the effect of the irrigation of salad crops with treated wastewater of various

qualities. When poor quality trickling filter effluent (106 FC per 100 ml) was used

to spray-irrigate lettuces, the initial level of indicator bacteria on the lettuces (106

FC/100g) reflected the bacteriological quality of the irrigation.

In studies of drip and furrow irrigation of lettuces and radishes with waste

stabilization pond effluent which had a FC count slightly higher than the WHO

recommendation of 1000 per 100 ml (1700 - 5000 FC per 100 ml geometric

mean count) crop contamination levels varied considerably. Under dry weather

conditions they were, at worst, of the orders of 103 and 104 Escherichia coli per

100g for radishes and lettuces respectively, and salmonellae were always

absent. The quality was better than that of locally sold lettuces (which had a

geometric mean FC count, based on 172 samples, of 1 x 106 per 100g).

However, when rainfall occurred, E. coli numbers increased and salmonellae

were isolated from lettuce surfaces (Bastos and Mara, 1995).

When furrow irrigation was used, the quality of lettuces in covered plots improved

to acceptable levels (103 FC/100g) within 3 days of cessation of irrigation and

was E.coli free after 9 days. However, results indicated that crops in uncovered

plots were recontaminated with bacteria from contaminated soils after significant

rainfall and regrowth of E.coli on crop surfaces was observed. Radishes were 19

prone to low level long term contamination with E.coli (up to 20 days).


These studies show that irrigating salad crops with effluent from conventional

treatment plants can result in unacceptable levels of bacterial contamination of

crops (unless a period of cessation of irrigation occurs before harvest) whereas

use of better quality effluents from waste stablilisation ponds results in

acceptable levels of bacterial contamination.

Studies in Israel have investigated the use of effluent from wastewater storage

reservoirs in unrestricted irrigation of vegetable and salad crops (Armon et al,

1994). When vegetables were irrigated with poor quality effluent (up to 107

FC/100ml of eluant solution) high levels of faecal indicator bacteria were detected

(up to 105 FC/100ml). However, when vegetables were irrigated with better

quality effluent (0-200 FC/100ml) from a storage reservoir with a lower organic

loading, faecal coliform levels on crops were generally very low, less than 103

FC/100ml and often lower (the data presented do not allow for greater specificity

about the levels) with a maximum of 104 FC/100ml. It is necessary to treat

wastewater effluents to an extent that no residual contaminants are detected on

the irrigated crops, but could alternatively be interpreted as showing that use of

treated wastewater meeting WHO (1989).

4.11 Studies on contamination of vegetable crops with nematode eggs

Experimental studies in NE Brazil and Leeds UK, investigated the consumer risk

from nematode infection (Ascaris lumbricoides and Ascaridia galli respectively)

from wastewater-irrigated lettuces (Ayres et al., 1992; Stott et al., 1994). In Brazil,

when raw wastewater (>100 nematode eggs/l) was used to spray-irrigate lettuce,

harvested crops were contaminated with mean values of up to 60 eggs / plant

after 5 weeks irrigation.

Irrigation with effluent from the anaerobic pond of a series of waste stabilisation

ponds (>10 eggs/l) reduced levels of nematode contamination on lettuce to

around 0.6 eggs/plant at harvest and produced a better quality of lettuce than

that sold in the local market. When facultative pond effluent (<0.5 eggs/l) was


used for irrigation, no eggs were detected on crops. Lettuces irrigated with

maturation pond effluent (0 eggs/l) were also not contaminated despite growing

uncovered plants in heavily contaminated soil containing >1200 Ascaris

eggs/100g indicating that neither irrigation nor rainfall resulted in recontamination

of crops.

In the UK, spray-irrigation of lettuce with poor quality wastewater (50 nematode

eggs/l) resulted in contamination of around 2.2 eggs/plant at harvest. When

wastewater at the WHO quality of = 1 eggs/l was used for irrigation, very slight

contamination was found on a few plants at around 0.3 eggs/plant. However, no

transmission of A. galli infection was found from wastewater irrigated crops using

animal studies although the infective dose is very low at less than 5 embryonated

eggs. The results collectively show that irrigation with wastewater of WHO (1989)

quality resulted in no contamination of lettuce at harvest (0.5 eggs/l) or very slight

contamination on a few plants (6%) with eggs that were either degenerate or not

infective.

However, a few nematode eggs on harvested plants were viable, but not yet

embryonated (20% A. lumbricoides on >100 eggs/l irrigated crops; <0.1 A. galli

eggs/plant irrigated with 1-10 eggs/l) and so crops with a long shelf life can

represent a potential risk to consumers as these eggs might have time to become

infective.

4.12 Human Safety and Control

Human safety control measures should cover the population group at risk.

Effective guidelines for health protection should be: feasible to implement;

adaptable to local social, economic, and environmental factors; and include the

following elements:

Evidence-based health risk assessment

Guidance for managing risk (including options other than wastewater

treatment)


Strategies for guideline implementation (including progressive implementation

where necessary).

The protection of public health can best be achieved by using a ‘multiple barriers’

approach that interrupts the flow of pathogens from the environment (wastewater,

crops, soil etc.) to people. Human pathogens in the fields do not necessarily

represent a health risk if other suitable health protection measures can be taken.

These measures may prevent pathogens from reaching the worker or the crop or,

by selection of appropriate crops (e.g. cotton), may prevent pathogens on the

crop from affecting the consumer (Mara and Cairncross, 1989). The measures

available for health protection can thus be grouped into five main categories:

Waste treatment

Crop restriction. Crop restriction can be used to protect the health of

consumers when water of sufficient quality is not available for unrestricted

irrigation. For example, water of poorer quality can be used to irrigate such

non-vegetable crops as cotton, or crops that will be cooked before

consumption (e.g. potatoes). It provides protection to farm workers and their

families where low-quality effluents are used in irrigation or where wastewater

is used indirectly, i.e. through contaminated surface water (Blumenthal et al.,

2000b). Crop restriction is therefore not an adequate single control measure,

but should be considered as part of an integrated system of control. To

provide protection for both workers and for the consumers, it should be

complemented by such other measures as partial waste treatment, controlled

application of wastes, or human exposure control (Mara and Cairncross,

1989).

Human exposure control Agricultural field workers are at high potential – and

often actual – risk, especially from parasitic infections.

Irrigation technique the choice of wastewater application method can have

impact on the health protection of farm workers, consumers, and nearby

communities. Spray/sprinkler irrigation has the highest potential to spread

contamination on crop surfaces and affect nearby communities. Bacteria and

viruses (but not intestinal nematodes) can be transmitted through aerosols to

nearby communities. Where spray/sprinkler irrigation is used with wastewater


it may be necessary to set up a buffer zone, e.g. 50–100 m from houses and

roads, to prevent health impacts on local communities (Mara and Cairncross,

1989). Farm workers and their families are at the highest risk when furrow or

flood irrigation techniques are used. This is especially true when protective

clothing is not worn and earth is moved by hand (Blumenthal et al., 2000b).

Localised irrigation techniques, e.g. bubbler, drip, trickle offer farm workers

the most health protection because they apply wastewater directly to the

plants. Although these techniques are generally the most expensive to

implement, drip irrigation has recently been adopted by some farmers in Cape

Verde and India (FAO, 2001; Kay, 2001).

Chemotherapy and vaccination. This might include chemotherapeutic control

of intense nematode infections in children and control of anaemia in both

children and adults, especially women and post-menarche girls.

Chemotherapy must be reapplied at regular intervals to be effective. The

frequency required to keep worm burdens at a low level (e.g. as low as those

in the rest of the population) depends on the intensity of the transmission, but

treatment may be required 2–3 times a year for children living in endemic

areas (Montresor et al., 2002; Mara and Cairncross, 1989). Albonico et al.

(1998) found that re-infection with helminths could return to pre-treatment

levels within 6 months of a mass chemotherapy campaign if the prevailing

conditions did not change.Chemotherapy and immunisation cannot normally

be considered adequate strategies to protect farm workers and their families

exposed to raw wastewater or excreta. However, where such workers are

organised within structured situations, such as on government or company

farms, these treatments could be beneficial as palliative measures, pending

improvement in the quality of the wastes used, or the adoption of other control

measures, e.g. protective clothing (Mara and Cairncross, 1989).

It will often be desirable to use a combination of several methods. For example,

crop restriction may be sufficient to protect consumers, but will need to be

supplemented by additional measures to protect agricultural workers. Sometimes

partial treatment to a less-demanding standard may be sufficient if combined with

other measures. The feasibility and efficacy of any combination will depend on


many factors that must be carefully considered before any option is put into

practice (Mara and Cairncross, 1989). These factors will include the following:

Availability of resources (labour, funds, land)

Existing social and agricultural practices

Market demand for wastewater-irrigated products

Existing patterns of excreta-related disease. For example, if sufficient funds

and/or sufficient land are not available for wastewater treatment, some of the

other three types of health protection measure will be needed.

The following specific measures ought to be adopted: The use of appropriate footwear and protective clothing to reduce hookworm

infection. For example, the exposure of agricultural field workers to hookworm

infection can be reduced if the workers use appropriate footwear. This may be

more difficult to achieve than it seems, because in many areas traditional

irrigation is carried out by scantily clad farmers.

The use of gloves (particularly crop handlers).

Health education.

Personal hygiene (increased levels of hygiene).

Immunisation against typhoid fever and hepatitis A and B. Immunization,

another preventive measure, may be feasible against certain diseases (for

example, typhoid and hepatitis A), but not against others (helminthic

infections and diarrheal diseases). Curative health measures would require

adequate) medical facilities to treat diarrhea, amoebiasis, and severe

nematode infections.

Provision of adequate medical facilities to treat diarrhoeal diseases

Protection of consumers can be achieved by: Cooking of vegetables and meat and boiling milk.

High standards of personal and food hygiene.

Health education campaigns.

Meat inspection, where there is risk of tapeworm infections.

Ceasing the application of wastes at least two weeks before cattle are allowed

to graze (where there are risks of bovine cysticercosis).


Ceasing the irrigation of fruit trees two weeks before the fruits are picked,

and not allowing fruits to be picked up from the ground.

Provision of information on the location of wastewater-irrigated fields together

with the posting of warning notices along the edges of the fields.

Hygiene promotion and educational sanitation seminars to people and especially

to children and promotion of hand washing is effective to reduce faecal-oral

disease transmission. This can cut the transmission of diarrhoeal disease.It is

critically important to dispose of faeces particularly childrens faeces in a safe

manner. Children are the victims of many diseases such as diarrhoeal and other

transmitted illnesses and in many cases are the source of pathogens.Designing

and promoting sanitation programmes to schools and other seminars may we

can manage to reduce the spread of diseases which they are associated with

waste and excreta. When water sanitation and hygiene are applied waterborne

illnesses can be reduce a lot.

There is no epidemiological evidence that aerosols from sprinklers cause

significant risks of pathogen contamination to people living near wastewater

irrigated fields. However, in order to allow a reasonable margin of safety and to

minimise the nuisance caused by odours, a minimum distance of 100 m should

be kept between sprinkler-irrigated fields and houses and roads as mentioned

before.

In agricultural and aquacultural reuse schemes and the risks to consumers can

be reduced if the food is cooked thoroughly before it is consumed and if high

standards of hygiene are maintained. Food hygiene should be emphasized in

health education, seminars, and campaigns. Vegetables usually eaten raw

should not be irrigated with wastewater, even if treated. Where the irrigation of

crops relies on wastewater, standards at least equal to the 1989 WHO guidelines

should be applied.


Local residents should be informed of the location of all fields where wastewater

is used so they can avoid them and prevent their children from entering them.

Warning notices (using symbols) should be posted along field borders and at

water taps.

Special precautions should be taken to ensure that workers, residents, and

visitors do not use wastewater for drinking or domestic purposes, either

accidentally or for lack of an alternative. A fundamental exposure-control

measure is to provide an adequate potable water supply. Moreover, all

wastewater channels, pipes, and outlets should be clearly marked (preferably

painted a characteristic color). Identification should be through colour coding and

marking.

The nonpotable system should be set apart from potable system or can be

stamped or marked CAUTION NONPOTABLE WATER-DO NOT DRINK OR CAUTION RECLAIMED WATER- DO NOT DRINK or the pipe may be wrapped

in purple polyethylene vinyl wrap. Outlet fittings should be of a special type to

prevent misuse.


5. Crops

5.1 Categorization of Crops

From the point of view of human consumption and potential health hazards,

crops and cultivated plants may be classified into the following groups (Table 5-

1): Table 5-1: Groups of cultivated plants

Categories of cropsi. Food crops those eaten uncooked

those eaten after cookingii. Forage and feed crops direct access by animals

those fed to animals after harvesting iii. Landscaping plants unprotected areas with public access

semi-protected areas iv. Afforestation plants commercial (fruit, timber, fuel and charcoal)

environmental protection (including sand stabilization)

Source: Shuval et al. 1986

In terms of health hazards, treated effluent with a high microbiological quality is

necessary for the irrigation of certain crops, especially vegetable crops eaten

raw, but a lower quality is acceptable for other selected crops, where there is no

exposure to the public. The WHO (1989) Technical Report No. 778 suggested a

categorization of crops according to the exposed group and the degree to which

health protection measures are required, as shown in Table 5-2.

The practice of crop restriction infers that crops that are allowed to be irrigated

with wastewater are restricted to those specified under category B. This category

protects consumers but additional protective measures are necessary for farm

workers.

Although it appears simple and in practice it is very difficult to implement and to

enforce crop restriction policies. A crop restriction policy is effective for health

protection only if it is fully implemented and enforced. It requires a strong

institutional framework and the capacity to monitor and to control compliance with

the established crop restriction regulations.


Table 5-2: Categorization of crops in relation to exposed group and health control measure.Category A Protection required for consumers, agricultural workers, and the general public. Includes crops likely to be eaten uncooked, spray-irrigated fruits and grass (sports field,

public parks and lawns);

Category B Protection required for agricultural workers only. Includes cereal crops, industrial crops (such as cotton and sisal), food crops for canning,

fodder crops, pasture and trees. In certain circunstances some vegetable crops might be considered as belonging to

Category B if they are not eaten raw (potatoes, for instance) or if they grow well above ground (for example, chillies), in much cases it is necessary to ensure that the crop is not contaminated by sprinkler irrigation or by falling on to the ground, and that contamination of kitchens by such crops, before cooking, does not give rise to a health risk.

Source: WHO, 1989

Farmers should be advised of the importance and necessity of the restriction

policy and be assisted in developing a balanced mix of crops which makes full

use of the available partially-treated waste-water. The idea of irrigating with

wastewater, particularly treated wastewater, does not appear to arouse

appreciable repugnance where it is being implemented or proposed. Although in

certain areas some farmers have refused to substitute treated wastewater for

available freshwater, other farmers of similar background in the same area have

readily accepted wastewater irrigation.

In contrast to the quality standards designed to minimize public health risks,

guidelines reflecting the effect of wastewater quality on plant growth arouse little

controversy. Whether irrigation water is derived from wastewater, surface water,

or groundwater, it will contain varying amounts of beneficial or detrimental

substances. The nature and level of these substances wil determine its suitability

to irrigate specific crops. Crop selection depends not only on the characteristics

of the irrigation water, but also on soil conditions and climate. Below a useful

order arranging crops in declining potencial to transmit pathogens if irrigated with

treated effluent. Crops at the top of the list pose the maximum hazard and the

ones at the bottom have minimum risks.

Vegetable eaten raw

Vegetables eaten cooked


Ornamental raised for sale in greenhouses

Trees producing fruits eaten raw without peeling

Lawns in amenity areas of unlimited access to the public

Trees producing fruits eaten raw after peeling

Lawns and other trees in amenity areas of limited access

Fodder crops

Trees producing nuts and other similar trees

Industrial crops

5.2 Restrictions on types of crops irrigated with wastewater

The three categories of irrigated crops are presented in increasing order of public

health risk. A different level of wastewater treatment should be provided for each

category. For category A crops would be irrigated with the lowest quality effluent

and category C with the highest quality effluent (Shuval et al., 986).

Category A – Low Risk

Crops not for human consumption (for example cotton).

Crops normally processed by heat or drying before human consumption

(grains, oilseeds, sugar beets).

Vegetables and fruit grown exclusively for canning or other processing that

effectively destroys pathogens.

Fodder crops and other animal feed crops sun-dried and harvested before

consumption by animals.

Landscape irrigation in fenced areas without public access (nurseries, forests,

greenbelts).

Category B – Medium Risk

Pasturelands, green fodder crops.

Crops for human consumption that do not come into direct contact with

wastewater on condition that no windfall be marketed (orchards, vine crops –

tomatoes, cucumbers, and vineyards irrigated by surface or drip irrigation).


Crops for human consumption normally eaten only after cooking (potatoes,

eggplant, beet roots).

Crops for human consumption, uncooked, the peel of which is not eaten

(melons, citrus, bananas, nuts, groundnuts).

Spray irrigation regardless of type of crop if at least 1,000m from residencial

areas or other areas with public access.

Below illustrated, are the main treatment trains for agriculture wastewater (Figure

5-1).

Figure 5-1: Treatments for agriculture wastewater use

Category C – High Risk


Raw sewage

Pre-treatment

Primary settling

Activated Sludge

Vegetables eaten raw

Clarifier

Filtration

Disinfection (Cl2/ UV/ O3)

TRAIN 3

Raw sewage

Pre-treatment

Activated Sludge


Pasture, cooked vegetables, fruits

Primary settling

TRAIN 2

Clarifier

Raw sewage

Pre-treatment

Coagulation/Flocculation


Industrial crops, forest

TRAIN 1

Any crops for human consumption normally consumed uncooked and grown

in direct contact with wastewater effluent (fresh garden vegetables such as

lettuce, tomatoes, carrots, or spray irrigated fruit).

Landscape irrigation in areas with free public access immediately after

irrigation on condition that, during spray irrigation, areas are fenced so that

there is no public access within 15m of wetted irrigation zones (golf courses,

Lawns, parks).

Spray irrigation regardless of type of crop within 100m of residencial areas or

places of public access, such as roads and parks, on condition that there is

no public accesss within 15m of the wetted irrigation zones.

5.3 Crop selection considerations and criteria

Crop selection should be based on three kinds of criteria:

Suitability of the crop to the general agronomic conditions of the site,

considering climate, soils, markets, and so on. In general, any of the crops

grown by local farmers under irrigation would be considered suitable

according to this criterion.

Constraints on crop production due to water quality changes, that is, salinity

and toxic effects of specific ions.

Constraints on crop utilization or marketing imposed by public health

considerations or regulations, considering both pathogens and toxic chemical

compounds.

Nevertheless, a lower quality of water is acceptable for irrigation of certain types

of crop and corresponding levels of exposure to the groups at risk, because

lower quality waters will affect consumers and other exposed groups such as

field workers and crop handlers. For example, crops which are normally cooked,

such as potatoes, or industrial crops such as cotton and sisal, do not require a

high quality wastewater for irrigation.

The likelihood of succeeding is greater where:


A law-abiding society exists or the restriction policy is strongly enforced.

A public body controls the allocation of wastewater under a strong central

management.

There is adequate demand for the crops allowed under the policy and they

fetch a reasonable price.

There is little market pressure in favour of crops in category A.

Table 5-3 presents the water requirements of some selected crops, reported by

Doorenbos and Kassam (FAO, 1979).

Table 5-3: Water requirements, sensitive to water supply and water utilization efficiency of some selected crops

Crop Water requirements (mm/growing

period)

Sensitivity to water supply (ky)

Water utilization efficiency for harvested yield, Ey, kg/m3 (% moisture)

Alfalfa 800-1600 low to medium-high (0.7-1.1) 1.5-2.0 hay (10-15%)Banana 1200-2200 High (1.2-1.35) Plant crop: 2.5-4, ratoon: 3.5-6, fruit (70%)Bean 300-500 medium-high (1.15) Lush: 1.5-2.0 (80-90%), dry: 0.3-0.6 (10%)Cabbage 380-500 medium-low (0.95) 12-20, head (90-95%)Citrus 900-1200 low to medium-high (0.8-1.1) 2-5, fruit (85%, lime: 70%)Cotton 700-1300 medium-low (0.85) 0.4-0.6, seed cotton (10%)Groundnut 500-700 Low (0.7) 0.6-0.8, unshelled dry nut (15%)Maize 500-800 High (1.25) 0.8-1.6, grain (10-13%)Potato 500-700 medium-high (1.1) 4-7, fresh tubers (70-75%)Rice 350-700 High 0.7-1.1, paddy (15-20%)Safflower 600-1200 Low (0.8) 0.2-0.5, seed (8-10%)Sorghum 450-650 medium-low (0.9) 0.6-1.0, grain (12-15%)Wheat 450-650 medium high (spring: 1.15;

winter: 1.0)0.8-1.0, grain (12-15%)

Source: FAO, 1979

5.3.1 Effects of salinity on crops

Not all plants respond to salinity in a similar manner. Some crops can produce

acceptable yields at much higher soil salinity than others. This is because some

crops are better able to make the needed osmotic adjustments, enabling them to

extract more water from a saline soil. The ability of a crop to adjust to salinity is

extremely useful. In areas where a build-up of soil salinity cannot be controlled at

an acceptable concentration for the crop being grown, an alternative crop can be

selected that is both more tolerant of the expected soil salinity and able to

produce economic yields. There is an 8-10 fold range in the salt tolerance of


agricultural crops. This wide range in tolerance allows for greater use of

moderately saline water, much of which was previously thought to be unusable. It

also greatly expands the acceptable range of water salinity (ECw) considered

suitable for irrigation.

The relative salt tolerance of most agricultural crops is known well enough to give

general salt tolerance guidelines. Table 5-4, 5-5, 5-6, and 5-7 presents a list of

crops classified according to their tolerance and sensitivity to salinity. The

following general conclusions can be drawn from these data:

Full yield potential should be achievable with nearly all crops when using

water with salinity less than 0.7 dS/m.

When using irrigation water of slight to moderate salinity (i.e. 0.7-3.0 dS/m),

full yield potential is still possible but care must be taken to achieve the

required leaching fraction in order to maintain soil salinity within the tolerance

of the crops. Treated sewage effluent will normally fall within this group.

For higher salinity water (more than 3.0 dS/m) and sensitive crops, increasing

leaching to satisfy a leaching requirement greater than 0.25 to 0.30 might not

be practicable because of the excessive amount of water required. In such a

case, consideration must be given to changing to a more tolerant crop that will

require less leaching, to control salts within crop tolerance levels. As water

salinity (ECw) increases within the slight to moderate range, production of

more sensitive crops may be restricted due to the inability to achieve the high

leaching fraction needed, especially when grown on heavier, more clayey soil

types.

Table 5-4: Salt moderately tolerant agricultural crops


MODERATELY TOLERANTFibre, Seed and Sugar CropsCowpea Vigna unguiculataOats Avena sativaRye Secale cerealeSafflower Carthamus tinctoriusSorghum Sorghum bicolorSoybean Glycine maxTriticale X TriticosecaleWheat Triticum aestivumWheat, Durum Triticum turgidumGrasses and Forage CropsBarley (forage) Hordeum vulgareBrome, mountain Bromus marginatusCanary grass, reed Phalaris, arundinaceaClover, Hubam Melilotus albaClover, sweet MelilotusFescue, meadow Festuca pratensisFescue, tall Festuca elatiorHarding grass Phalaris tuberosaPanic grass, blue Panicum antidotaleRape Brassica napusRescue grass Bromus unioloidesRhodes grass Chloris gayanaGrasses and Forage CropsRyegrass, Italian Lolium italicum multiflorumRyegrass, perennial Lolium perenneSudan grass Sorghum sudanenseTrefoil, narrowleaf birdsfoot Lotus corniculatus tenuifoliumTrefoil, broadleaf L. corniculatus arvenisWheat (forage) Triticum aestivumWheatgrass, standard crested Agropyron sibiricumWheatgrass, intermediate Agropyron intermediumWheatgrass, slender Agropyron trachycaulumWheatgrass, western Agropyron smithiiWildrye, beardless Elymus triticoidesWildrye, Canadian Elymus canadensisVegetable CropsArtichoke Helianthus tuberosusBeet, red Beta vulgarisSquash, zucchini Cucurbita pepo melopepoFruit and Nut CropsFig Ficus caricaJujube Ziziphys jujubaOlive Olea europaeaPapaya Carica papayaPineapple Ananas comosusPomegranate Punica granatumSource: FAO, 1985

Table 5-5: Salt moderately sensitive agricultural cropsMODERATELY SENSITIVE


Fibre, Seed and Sugar CropsBroadbean Vicia fabaCastorbean Ricinus communisMaize Zea maysFlax Linum usitatissimumMillet, foxtail Setaria italicaGroundnut/peanut Arachis hypogaeaRice, paddy Oryza sativaSugarcane Saccarum officinarumSunflower Helianthus annuus palustrisGrasses and Forage CropsAlfalfa Medicago sativaBentgrass AgrostisstoloniferapalustrisBluestem, Angleton Dichanthium aristatumBrome, smooth Bromus inermisBuffel grass Cenchrus ciliarisBurnet Poterium sanguisorbaGrasses and Forage CropsClover, Berseem Trifolium alexandrinumClover, ladino Trifolium repensClover, red Trifolium pratenseClover, strawberry Trifolium fragiferumClover, white Dutch Trifolium repensCorn (forage) (maize) Zea maysCowpea (forage) Vigna unguiculataDallis grass Paspalum dilatatumFoxtail, meadow Alopecurus pratensisVegetable CropsBroccoli Brassica oleracea botrytisBrussel sprouts B. oleracea gemmiferaCabbage B. oleracea capitataCauliflower B. oleracea botrytisCorn, sweet Zea maysCucumber Cucumis sativusEggplant Solanum melongena esculentumKale Brassica oleracea acephalaKohlrabi B. oleracea gongylodeLettuce Latuca sativaMuskmelon Cucumis melonPepper Capsicum annumPotato Solanum tuberosumPumpkin Cucurbita peop pepoRadish Raphanus sativusSpinach Spinacia oleraceaFruit and Nut CropsGrape Vitis sp.Source: FAO, 1985

Table 5-6: Salt sensitive agricultural cropsSENSITIVE


Fibre, Seed and Sugar CropsBean Phaseolus vulgarisGuayule Parthenium argentatumSesame Sesamum indicumVegetable CropsBean Phaseolus vulgarisCarrot Daucus carotaFruit and Nut CropsAlmond Prunus dulcisApple Malus sylvestrisApricot Prunus armeniacaAvocado Persea americanaBlackberry Rubus sp.Mango Mangifera indicaOrange Citrus sinensisPassion fruit Passiflora edulisPeach Prunus persicaPear Pyrus communisStrawberry Fragaria sp.Persimmon Diospyros virginianaPlum: Prune Prunus domesticaPummelo Citrus maximaRaspberry Rubus idaeusSource: FAO, 1985

5.3.2 Toxicity hazards on crops

A toxicity problem is different from a salinity problem in that it occurs within the

plant itself and is not caused by water shortage. Toxicity normally results when

certain ions are taken up by plants with the soil water and accumulate in the

leaves during water transpiration to such an extent that the plant is damaged.

The degree of damage depends upon time, concentration of toxic material, crop

sensitivity and crop water use and, if damage is severe enough, crop yield is

reduced. Common toxic ions in irrigation water are chloride, sodium, and boron,

all of which will be contained in sewage. Damage can be caused by each

individually or in combination. Not all crops are equally sensitive to these toxic

ions. Some guidance on the sensitivity of crops to sodium, chloride and boron are

given in Tables 5-7, 5-8 and 5-9, respectively. However, toxicity symptoms can

appear in almost any crop if concentrations of toxic materials are sufficiently high.

Toxicity often accompanies or complicates a salinity or infiltration problem,

although it may appear even when salinity is not a problem.


The toxic ions of sodium and chloride can also be absorbed directly into the plant

through the leaves when moistened during sprinkler irrigation. This typically

occurs during periods of high temperature and low humidity. Leaf absorption

speeds up the rate of accumulation of a toxic ion and may be a primary source of

the toxicity.

Table 5-7: Relative tolerance of selected crops to exchangeable sodiumSensitive Semi-tolerant Tolerant

Avocado (Persea americana) Carrot Alfalfa (Daucus carota)Deciduous Fruits Clover, Ladino Barley (Trifolium repens)Nuts Bean, green (Phaseolus vulgaris) Dallisgrass Beet, garden (Paspalum dilatatum)Cotton (at germination)(Gossypium hirsutum)

Fescue, tall Beet, sugar (Festuca arundinacea)

Maize (Zea mays) Lettuce Bermuda grass (Lactuca sativa)Peas (Pisum sativum) Bajara Cotton (Pennisetum typhoides)Grapefruit (Citrus paradisi) Sugarcane Paragrass (Saccharum officinarum)Orange (Citrus sinensis) Berseem Rhodes grass (Trifolium alexandrinum)Peach (Prunus persica) Benji Wheatgrass, crested (Mililotus parviflora)Tangerine (Citrus reticulata) Raya Wheatgrass, fairway (Brassica juncea)Mung (Phaseolus aurus) Oat Wheatgrass, tall (Avena sativa)Mash (Phaseolus mungo) Onion Karnal grass (Allium cepa)Lentil (Lens culinaris) Radish (Raphanus

sativus)

Urban wastewater may contain heavy metals at concentrations which will give

rise to elevated levels in the soil and cause undesirable accumulations in plant

tissue and crop growth reductions. Heavy metals are readily fixed and

accumulate in soils with repeated irrigation by such wastewaters and may either

render them non-productive or the product unusable. Surveys of wastewater use

have shown that more than 85 % of the applied heavy metals are likely to

accumulate in the soil, most at the surface. Any wastewater use project should

include monitoring of soil and plants for toxic materials.


Table 5-8: Chloride tolerance of some fruit crop cultivars and rootstocksCrop Rootstock or

CultivarMaximum permissible Cl- without leaf injury1

Root zone (Cle) (me/l)

Irrigation water (Clw)2 3 (me/l)

RootstocksAvocado (Persea americana)

West Indian 7.5 5.0 Guatemalan 6.0 4.0 Mexican 5.0 3.3

Citrus (Citrus spp.) Sunki Mandarin 25.0 16.6 Grapefruit Cleopatra mandarin Rangpur lime Sampson tangelo 15.0 10.0 Rough lemon Sour orange Ponkan mandarin

Grape(Vitis spp.) Salt Creek 40.0 27.0 Dog Ridge 30.0 20.0

Stone Fruits (Prunus spp.)

Marianna 25.0 17.0 Lovell, Shalil 10.0 6.7 Yunnan 7.5 5.0 Cultivars

Berries (Rubus spp.) Boysenberry 10.0 6.7 Olallie clackberry 10.0 6.7 Indian SUmmer 5.0 3.3 Raspberry

Grape(Vitis spp.) Thompson seedless 20.0 13.3 Perlette 20.0 13.3 Cardinal 10.0 6.7 Black Rose 10.0 6.7

Strawberry (Fragaria spp.)

Lassen 7.5 5.0

Shasta 5.0 3.3 1 For some crops, the concentration given may exceed the overall salinity tolerance of that crop and cause some reduction in yield in addition to that caused by chloride ion toxicities. 2 Values given are for the maximum concentration in the irrigation water. The values were derived from saturation extract data (ECe) assuming a 15-20 percent leaching fraction and ECd = 1.5 ECw. 3 The maximum permissible values apply only to surface irrigated crops. Sprinkler irrigation may cause excessive leaf bum at values far below these.

Source: FAO/Unesco, 1973


Table 5-9: Relative Boron tolerance of agricultural crops1

VERY SENSITIVE (<0.5 mg/l)Lemon Blackberry Citrus limon Rubus spp.

SENSITIVE (0.5-0.75 mg/l)Avocado Persimmon Persea americana Diospyros kakiGrapefruit Fig, kadota Citrus X paradisi Ficus caricaOrange Grape Citrus sinensis Vitis viniferaApricot Walnut Prunus armeniaca Juglans regiaPeach Pecan Prunus persica Carya illinoiensisCherry Cowpea Prunus avium Vigna unguiculataPlum Onion Prunus domestica Allium cepa

SENSITIVE (0.75-1.0 mg/l)Garlic Lupine Allium sativum Lupinus hartwegiiSweet potato Strawberry Ipomoea batatas Fragaria spp.Wheat Artichoke, Jerusalem Triticum eastivum Helianthus tuberosusBarley Bean, kidney Hordeum vulgare Phaseolus vulgarisSunflower Bean, lima Helianthus annuus Phaseolus lunatusBean, mung Groundnut/Peanut Vigna radiata Arachis hypogaeaSesame Sesamum indicum

MODERATELY SENSITIVE (1.0-2.0 mg/l)Pepper, red Radish Capsicum annuum Raphanus sativusPea Potato Pisum sativa Solanum tuberosumCarrot Cucumber Daucus carota Cucumis sativus

MODERATELY TOLERANT (2.0-4.0 mg/l)Lettuce Artichoke Lactuca sativa Brassica junceaCabbage Tobacco B. oleracea capitata Melilotus indicaCelery Mustard Apium graveolens Cucurbita pepoTurnip Clover, sweet Brassica rapa Zea maysBluegrass, Kentucky Squash Poa pratensis Nicotiana tabacumOats Cynara scolymus Avena sativa Maize

TOLERANT (4.0-6.0 mg/l)Sorghum Parsley Sorghum bicolor Petroselinum crispumTomato Beet, red L. lycopersicum Beta vulgarisAlfalfa Sugarbeet Medicago sativa Beta vulgarisVetch, purple Vicia benghalensis

VERY TOLERANT (6.0-15.0 mg/lCotton Asparagus Gossypium hirsutum Asparagus officinalis1 Maximum concentration tolerated in soil water without yield or vegetative growth reductions. Boron tolerances vary depending upon climate, soil conditions and crop varieties. Maximum concentrations in the irrigation water are approximately equal to these values or slightly less.

Source: Maas, 1984


Table 5-10: Threshold levels of trace elements for crop productionElement Recommended

maximum concentration (mg/l)

Remarks

Al (aluminium) 5.0 Can cause non-productivity in acid soils (pH < 5.5), but more alkaline soils at pH > 7.0 will precipitate the ion and eliminate any toxicity.

As (arsenic) 0.10 Toxicity to plants varies widely, ranging from 12 mg/l for Sudan grass to less than 0.05 mg/l for rice.

Be (beryllium) 0.10 Toxicity to plants varies widely, ranging from 5 mg/l for kale to 0.5 mg/l for bush beans.

Cd (cadmium) 0.01 Toxic to beans, beets and turnips at concentrations as low as 0.1 mg/l in nutrient solutions. Conservative limits recommended due to its potential for accumulation in plants and soils to concentrations that may be harmful to humans.

Co (cobalt) 0.05 Toxic to tomato plants at 0.1 mg/l in nutrient solution. Tends to be inactivated by neutral and alkaline soils.

Cr (chromium) 0.10 Not generally recognized as an essential growth element. Conservative limits recommended due to lack of knowledge on its toxicity to plants.

Cu (copper) 0.20 Toxic to a number of plants at 0.1 to 1.0 mg/l in nutrient solutions.F (fluoride) 1.0 Inactivated by neutral and alkaline soils.Fe (iron) 5.0 Not toxic to plants in aerated soils, but can contribute to soil acidification

and loss of availability of essential phosphorus and molybdenum. Overhead sprinkling may result in unsightly deposits on plants, equipment and buildings.

Li (lithium) 2.5 Tolerated by most crops up to 5 mg/l; mobile in soil. Toxic to citrus at low concentrations (<0.075 mg/l). Acts similarly to boron.

Mn (manganese) 0.20 Toxic to a number of crops at few-tenths to a few mg/l, but usually only in acid soils.

Mo (molybdenum) 0.01 Not toxic to plants at normal concentrations in soil and water. Can be toxic to livestock if forage is grown in soils with high concentrations of available molybdenum.

Ni (nickel) 0.20 Toxic to a number of plants at 0.5 mg/l to 1.0 mg/l; reduced toxicity at neutral or alkaline pH.

Pd (lead) 5.0 Can inhibit plant cell growth at very high concentrations.Se (selenium) 0.02 Toxic to plants at concentrations as low as 0.025 mg/l and toxic to

livestock if forage is grown in soils with relatively high levels of added selenium. As essential element to animals but in very low concentrations.

Ti (titanium) - Effectively excluded by plants; specific tolerance unknown.C (carbon) 0.10 Toxic to many plants at relatively low concentrations.Zn (zinc) 2.0 Toxic to many plants at widely varying concentrations; reduced toxicity

at pH > 6.0 and in fine textured or organic soils.1 The maximum concentration is based on a water application rate which is consistent with good irrigation practices (10 000 m3 per hectare per year). If the water application rate greatly exceeds this, the maximum concentrations should be adjusted downward accordingly. No adjustment should be made for application rates less than 10 000 m3 per hectare per year. The values given are for water used on a continuous basis at one site.

Source: Pratt, 1972


6. Irrigation Methods

Out of various irrigation methods used, modern technology might be of particular

interest in irrigating with treated wastewater. Selection of any method, whether

conventional or modern, should be handled carefully in order to operate the

irrigation system efficiently and safely. Selection of the appropriate irrigation

method depends on the quality of the effluent, crops to be grown, farmers

tradition, background and skill of the farmers and the potential risk to workers and

to public health.

6.1 Conventional Surface Irrigation methods

Flood irrigation of long borders or large basins, wetting almost the entire land

surface.

Furrow irrigation for row crops, wetting only part of the ground surface.

Small- basin irrigation, whereby water is delivered in sequence to small

basins (25- 50 cm2) or to individual trees (Pescod, 1992).

These methods are easy to implement, less costly and require no energy for

water application at the field level. Such methods, although are practiced and

suitable for many developing countries particularly whenever water is plentiful

and with relatively flat heavy to medium-textured soils.

The contact risk with these methods is high and implies an advanced level of

treatment to the effluent before use (Pescod, 1992).

6.2 Modern Irrigation methods

These are, in general, pressurized networks including pumps, flow-meters,

control valves and piped distribution, they include:

Sprinkler, including fixed units, hand-movable units, center pivots, side-rolls,

or mini-sprinklers, whereby all soil surfaces is wetted.


Localized surface systems, including trickle, bubbler systems and drip

systems (Pescod, 1992).

6.2.1 Flood irrigation

The

application

of irrigation

water

where the

entire

surface of

the soil is

covered by

ponded

water, (Figure 6-1).

Water is applied over the entire field to infiltrate into the soil (e.g. wild flooding,

contour flooding, borders, and basins).

In flood irrigation, a large amount of water is brought to the field and flows on the

ground among the crops. In regions where water is abundant, flood irrigation is

the cheapest method of irrigation and this low tech irrigation method is commonly

used by societies in developing countries. It should be applied only to flat lands

that do not concave or slope downhill so that the water can evenly flow to all parts

of the field, yet even so, about 50% of the water is wasted and does not get used

by the crops. Some of this wasted water accumulates at the edges of a field and

is called run-off. In order to conserve some of this water, growers can trap the

run-off in ponds and reuse it during the next round of flood irrigation. However a

large part of the wasted water can not be reused due to massive loss via

evaporation and transpiration.


Figure 6-1: Flood irrigation

http://www.tau.ac.il/~ecology/virtau/4-yaelb/glossary.htm


One of the advantages of flood irrigation is its ability to flush salts out of the soil,

which is important for many saline intolerant crops. However, the flooding causes

an anaerobic environment around the crop which can increase microbial

conversion of nitrogen from the soil to atmospheric nitrogen, or denitrification,

thus creating low nitrogen soil.

Surge flooding is an attempt at a more efficient version of conventional flood

irrigation in which water is released onto a field at scheduled times, thus reducing

excess run-off.

6.2.2 Furrow irrigation

Furrows are small, parallel channels, made to carry water in order to irrigate

crops (Figure 6-2). The crop is grown on the ridges between the furrows. The

method is suitable for a wide range of soil types, crops and land slopes.

Water is applied between ridges (e.g. level and graded furrows, contour furrows,

corrugations). Water reaches the ridge (where the plant roots are concentrated)

by capillary action.

A partial surface flooding method of irrigation normally used with clean-tilled

crops where water is applied in furrows or rows of sufficient capacity to contain

the designed irrigation system.

Furrow

irrigation is

actually a

type of

flood

irrigation in

which the

water

poured on


Figure 6-2: Furrow irrigation


the field is directed to flow through narrow channels between the rows of crops,

instead of distributing the water throughout the whole field evenly. The furrows

must all have equal dimensions, in order to guarantee that the water is

distributed evenly. Like flood irrigation, furrow irrigation is rather cheap in areas

where water is inexpensive.

Furrow irrigation does not wet the entire soil surface, and can reduce crop

contamination, because plants are grown on ridges. Complete health protection

cannot be guaranteed and the risk of contamination of farm workers is potentially

medium to high, depending on the degree of automation of the process. If the

treated wastewater is transported through pipes and delivered into individual

furrows by means of gated pipes, the risk to irrigation workers is minimum, which

may induce the development of disease vectors. Levelling of the land should be

carried out carefully and appropriate land gradients should be provided.

Furrow irrigation is suitable for many crops especially for crops that would be

damaged if their stem or crown is covered by water should be irrigated by

furrows.

The following crops can be irrigated with furrow irrigation:

Row crops such as maize, sunflower, sugarcane, and soybean

Crops that would be damaged by inundation (tomatoes, vegetables, potatoes,

beans)

Fruit trees (citrus, grape)

Broadcast crops (wheat)

It is also suited to the growing of tree crops. In the early stages of tree planting ,

one furrow alongside the tree row may be sufficient but as the trees develop then

two or more furrows can be constructed to provide sufficient water. Furrows can

be used in most soils types. Soils that crust easily are especially suited to furrow

irrigation because the water does not flow over the ridge and so the soil in which


the plants grow remains friable.The shape of furrows is influenced by the soil

type and the stream size.

The location of plants in a furrow system is not fixed and depends on natural

circumstances:

In areas with heavy rainfall, the plants should stand on top of the ridge in

order to prevent damage (waterlogging)

If water is scarce the plants may be put in the furrow itself, to benefit more

from the limited water

For winter and early spring crops in colder areas, the seeds may be plant on the

sunny side of the ridge. In hotter areas seeds may be planted on the shady side

of the ridge to protect them from the sun.

6.2.3 Basin Irrigation

For basin irrigation, flat areas of land surrounded by low bunds (Figure 6-3)

prevent water from flowing to the adjacent fields. Basin irrigation is used for rice

grown on flat lands. In general the basin method is suitable for crops that are

unaffected by standing in water for long periods. Other crops that can be irrigated

are:

Pastures

(alfalfa,

clover)

Trees

(citrus,

banana)

Crops

which are broadcast (cereals)

Some extent row crops such as tobacco.


Figure 6-3: Basin irrigation

Basin Irrigation is not suited to crops which can not stand in wet or waterlogged

conditions for periods longer than 24 hours. These are usually root and crops

such as potatoes, cassava, beet and carrots which require loose, well drained

soils.

The construct of basins is easier the more flat is the surface of the land. A

separation between rice and non-rice or other crops is made.Paddy rice is grown

on clayey soils. Rice could also be grown on sandy soils. Many other crops can

be grown on clays, loamy soils are preferred for basin irrigation so that

waterlogging can be avoided. Coarse sands are not recommended for basin

irrigation due to the high infiltration rate of the soil and also soils which form a

hard crust when dry are not suitable.The basins shape and size are determined

by the land slope, the soil type, the available stream size, the required depth of

the irrigation application and farming practices.

Basins should be small if the:

Slope of the land is steep

Soil is sandy

Stream size to the basin is small

Required depth of the irrigation application is small

Field preparation is done by hand or animal traction.

Basins can be large if the:

Slope of the land is gentle or flat

Soil is clay

Stream size to the basin is large

Required depth of the irrigation application is large

Field preparation is mechanize

Table 6-1: Conventional irrigation methods and suitable crops

Convetional Irrigation methods

Suitable crops

Flood irrigation Alfalfa


deep rooted close-growing crops orchards

Furrow irrigation Row crops such as maize, sunflower, sugarcane, and soybean

Crops that would be damaged by inundation (tomatoes, vegetables, potatoes, beans)

Fruit trees (citrus, grape) Broadcast crops (wheat)

Basin irrigation Pastures (alfalfa, clover) Trees (citrus, banana) Crops which are broadcast (cereals) Some extent row crops such as tobacco

A summary of the three above Conventional Surface Irrigation methods and the

suitable crops to be irrigated is shown in Table 6-1.

6.2.4 Sprinkler

Sprinkler irrigation (Figure 6-4) is similar to natural rainfall. Water is applied in the

form of a spray and reaches the soil in much the same way as rain (e.g. portable

and solid set sprinklers, travelling sprinklers, spray guns, center-pivot systems). A

planned

irrigation

system in

which water

is applied

by means

of

perforated

pipes or

nozzles

operated

under

pressure so

as to form a

spray pattern.


Figure 6-4: Sprinkler Irrigation

Sprinkler systems are the most common. They work on slopes with up to 30

percent grade and are not limited by wastewater quality. The lateral pipes

supplying water to the sprinklers should always be laid out along the land

whenever possible. This will minimize the pressure changes at the sprinklers and

provide a uniform irrigation. All types of crops can be irrigated using sprinkler

systems. Is suited for most row, field and tree crops and water can be sprayed

over or under the crop.

Large sprinklers are not recommended for irrigation of delicate crops such as

lettuce because the large water drops produced by the sprinklers may damage

the crop. Solid set sprinkler systems that are most often used in wastewater

reuse system are: center pivot, travelling gun, and travelling lateral systems also

have applications.

Sprinklers are suited to sandy soils with high infiltration rates but they can be

used to most soils. They are not suitable for soils which easily form a crust.

Some limitations to the use of sprinkler systems are the purchase, placement

costs, and field space for the equipment. Another limitation of sprinkler systems

is spray drift. Setbacks must be included in the field layout to minimize spray drift

onto roads and dwellings.

Typical sprinkler system irrigation has the following components (FAO, 2001):

Pump unit

Mainline and submainlines (sometimes)

Laterals

Sprinklers

To avoid problems of sprinkler nozzle blockage and spoiling the crop by coating it

with sediment the water must be clean and free of suspended sediments.

When water sprays from a sprinkler it brakes up into small drops between 0.5-4.0

mm in size. These drops fall close to the sprinkler and the larger ones fall close

to the edge of the wetted circle. Large drops damage delicated crops and soils so


it is better to use smaller sprinklers (small diameter nozzles). For good uniformity

several sprinklers must be operated close together. This uniformity can be

affected by wind and water pressure. For that reason sprinklers must be

positioned closely to reduce the effects of wind.

6.2.4.1 Center-PivotCenter-Pivot is an automated sprinkler

irrigation achieved by automatically rotating

the sprinkler pipe or boom, supplying water

to the sprinkler heads or nozzles, as a

radius from the centre of the field to be

irrigated. Water is delivered to the centre or

pivot point of the system. The pipe is

supported above the crop by towers at fixed

spacings and propelled by pneumatic,

mechanical, hydraulic, or electric power on wheels or skids in fixed circular paths

at uniform angular speeds.

Water is applied at a uniform rate by progressive increase of nozzle size from

the pivot to the end of the line. The depth of water applied is determined by the

rate of travel of the system. Single units are ordinarily about 1,250 to 1,300 feet

long and irrigate about a 130-acre circular area

6.2.4.2 Travelling GunTravelling

Gun is a

sprinkler

irrigation

system

consisting of a single large nozzle that rotates and is self-propelled. The name


Figure 6-5: Center Pivot

Figure 6-6: Travelling Gun

refers to the fact that the base is on wheels and can be moved by the irrigator or

affixed to a guide wire.

6.2.5 Drip systems

Drip irrigation is sometimes called trickle irrigation and is the dripping of water

onto the soil at very low rates from a system of small diameter plastic pipes fitted

with outlets called emitters or drippers. Water is applied close to the plants so a

little part of soil is wetted; the one near the roots of the plant (Figure 6-7). With

drip irrigation applications are more frequent and this provides high moisture

level in the soil.

While drip irrigation may be the most expensive method of irrigation, it is also the

most advanced and efficient method in respect to effective water use. Usually

used to irrigate row crops such as soft fruits and vegetables, tree and vine crops

where more than one emitters can be applied for each plant. Because is a high

cost system is applied only in high value crops. This system consists of

perforated pipes that are placed by rows of crops or buried along their root lines

and emit water directly onto the crops that need it. As a result, evaporation is

drastically reduced and 25% irrigation water is conserved in comparison to flood

irrigation. Drip irrigation is adaptable to any farmable slope and is suitable for

most soils. On clay soils water must be applied slowly to avoid surface water

ponding and runoff. On sandy soils is needed higher emitter discharge.

Water high in salts should be filtered before use because it might clog the

emitters and create a local buildup of high salinity soil around the plants if the

irrigation water contains soluble salts. If also the water contains algae, fertilizer

deposits and dissolved chemicals such as calcium and iron may also cause

blockage of the emitters.


A typical

drip

irrigation

system

contains the

following:

Pump

unit

Control

head

Main and submain lines

Laterals

Emitters or drippers

A planned drip irrigation system water is applied directly to the root zone of

plants by means of applicators (orifices, emitters, porous tubing, perforated pipe,

etc.) operated under low pressure with the applicators being placed either on or

below the surface of the ground.

Drip irrigation systems use low-rate emitters to deliver wastewater slowly to the

plant. Wastewater must be very low in solids, and disinfection may be required to

reduce biofilms that can clog emitters. Drip systems can be used on any slope

and are well suited to permanent planting, such as landscaping. The equipment

and installation costs for drip systems may be high, but they do not create spray

drift problems.

When compared with other systems, the main advantages of trickle or drip

irrigation (Pescot, 1992) are:

Increased crop growth and yield achieved by optimising the water, nutrients

and air regimes in the root zone.


Figure 6-7: Drip irrigation

High irrigation efficiency because there is no canopy interception, wind drift or

conveyance losses, and minimal drainage loss.

Minimal contact between farm workers and wastewater.

Low energy requirements because the trickle system requires a water

pressure of only 100-300 kPa (1-3 bar).

Low labour requirements because the trickle system can be easily automated,

even to allow combined irrigation and fertilisation

6.2.6 Bubbler Irrigation

A relatively

new

technique

called

"bubbler

irrigation»

that was

developed

for localised irrigation of tree crops avoids the needs for small orifices. This

system requires, therefore, less treatment of the wastewater but needs careful

setting for successful application (Figure 6-8).

Bubbler systems (bubblers, pipes, valves, trenches, and basins), like drip

systems, require routine maintenance. Bubbler systems are not immune to

vandalism and wear, particularly at commercial, institutional and multifamily sites.

In addition, the basins and trenches need to be kept clean to prevent overflow.

Because of higher flows, bubbler systems waste more water when leaks, breaks,

or over-scheduling problems occur.

According to Arizona Water Resource, (1999), bubblers are visible and problems

are noticeable - drip emitters and drip problems are invisible.

Bubblers require minimal filtration - soil, calcification, and bacteria clog drip

emitters.


Figure 6-8: Bubbler irrigation

Bubblers do not degrade in heat- drip emitters degrade in heat and flow

increases.

Bubbler flow rate and wetted area are easy to adjust - drip flow rates are

difficult to adjust.

Bubblers are durable and require little maintenance - drip emitters are fragile

and require far more maintenance.

The bubbler irrigation/water harvesting system is attractive - buried drip

irrigation systems are attractive.

6.2.7 Advantages and disadvantages of different methods of wastewater irrigation

Drip irrigation has many advantages over bubblers. The most important are

application of water directly in the plant's root zone and ability to water many

plants on one valve. Other benefits include multi-valving for mixed plantings with

varying water requirements in the same physical area; reduced weed growth and

surface evaporation; slow application rate which eliminates runoff and erosion;

ease in installation and repair; and lower overall installation cost. In some

situations bubblers can be effective, specifically with monocultures such as

hedges, orchards, lines of trees and areas of groundcover. Even in these cases,

however, uniformity and suffer if the grade is not level. Drip irrigation is much

more adaptable to unusual situations, such as clayey soils, slopes, hilly areas,

berms, and small, low density landscapes.

In Table 6-2 a generalized list of application methods and the advantages and

disadvantages of each one is shown.

Table 6-2: Advantages and disadvantages of different methods of wastewater irrigation in terms of disease transmission risks, water use efficiency, and cost.

Method ofapplication

Advantages Disadvantages

Surface irrigation include: Basin irrigation Furrow irrigation Border irrigation

Low cost, low level of wastewater treatment required

High potencial health risks to:o field workers,o crop handlers,o and consumers,

crop restrictions necessary, low water-use efficiency

Sprinkler and Microsprayer Medium water-use High cost of treatment,


Efficiency Potencial health risks to:o field workers,o local residents,o crop handlers,o to consumers, if irrigated crops

consumed raw.Localized irrigation( drip, bubbler )

Low health risks, High water-use efficiency

High cost of treatment for drip, somewhat less for bubbler irrigation, high cost of distribution

Source: Mara and Cairncross, 1989There is considerable scope for reducing the negative effects of wastewater use

in irrigation through the selection of appropriate irrigation methods.

A Basin or any Flood irrigation system involves complete coverage of the soil

surface with treated wastewater which is not normally an efficient method of

irrigation. This system contaminates root crops and vegetable crops growing near

the ground and, more than any other method, exposes field workers to the

pathogen content of wastewater.

Sprinkler, or spray, irrigation methods are generally more efficient in water use

because greater uniformity of application can be achieved. However, such

overhead irrigation methods can contaminate ground crops, fruit trees and farm

workers. In addition, pathogens contained in the wastewater aerosol can be

transported downwind and create a health hazard to nearby residents. Generally,

mechanised or automated systems have relatively high capital costs and low

labour costs compared with manually-operated sprinkler systems. Rough

levelling of the land is necessary for sprinkler systems in order to prevent

excessive head loss and to achieve uniformity of wetting. Sprinkler systems are

more affected by the quality of the water than surface irrigation systems, primarily

as a result of clogging of the orifices in the sprinkler heads but also due to

sediment accumulation in pipes, valves and distribution systems. There is also

the potential for leaf burn and phytotoxicity if the wastewater is saline and

contains excessive toxic elements. Secondary treatment systems that meet the

WHO microbiological guidelines have generally been found to produce an

effluent suitable for distribution through sprinklers, provided that the wastewater

is not too saline.


Further precautionary measures, such as treatment with sand filters or micro-

strainers and enlargement of the nozzle orifice to diameters not less than 5 mm,

are often adopted. Conventional irrigation, particularly when the soil surface is

covered with plastic sheeting or other mulch, uses effluent more efficiently. It

produces higher crop yields and certainly provides the greatest degree of health

protection to farm workers and consumers.

However, trickle and drip irrigation systems are expensive and require a high

quality of treated wastewater in order to prevent clogging of the orifices through

which water is released into the soil. In addition to the high capital costs of trickle

irrigation systems, another limiting factor in their use is that they are mostly suited

to the irrigation of crops planted in rows. Relocation of subsurface systems can

be prohibitively expensive. Special field management practices that may be

required when wastewater irrigation is performed include pre-planting irrigation,

blending of waste-water with other water supplies, and alternating treated

wastewater with other sources of supply.

The amount of wastewater to be applied depends on the rate of evapo-

transpiration from the plant surface, which is determined by climatic factors and

can therefore be estimated with reasonable accuracy, using meteorological data.

An extensive review of this subject is available in FAO (1984). Health risks from

irrigated crops are greatest when spray/sprinkler irrigation is used and risk to field

workers is greatest when food or furrow irrigation is used.

In terms of health hazards, treated effluent with a high microbiological quality is

necessary for the irrigation of certain crops, especially vegetable crops eaten

raw, but a lower quality is acceptable for other selected crops, where there is no

exposure to the public.

The different types of irrigation methods have been introduced. Under normal

conditions, the type of irrigation method selected will depend on water supply


conditions, climate, soil, crops to be grown, cost of irrigation method and the

ability of the farmer to manage the system. However, when using wastewater as

the source of irrigation other factors, such as contamination of plants and

harvested product, farm workers, and the environment, and salinity and toxicity

hazards, will need to be considered. There is considerable scope for reducing the

undesirable effects of wastewater use in irrigation through selection of

appropriate irrigation methods.

The choice of irrigation method in using wastewater is governed by the following

technical factors (Pesoct, 1992):

- the choice of crops,

- the wetting of foliage, fruits and aerial parts,

- the distribution of water, salts and contaminants in the soil,

- the ease with which high soil water potential could be maintained,

- the efficiency of application, and

- the potential to contaminate farm workers and the environment.

6.3 Proplems with water quality in irrigation

Four categories of potential management problems associated with water quality

in irrigation are:

Salinity

Specific Ion toxicity

Water infiltration rate

Other problems with the procedure

Table 6-3 presents some basic features of selected irrigation systems as

reported by Doneen and Westcot (FAO, 1988)

6.3.1 Salinity

Salinity is the most important parameter determining the suitability of water for

irrigation. It is a measure of total amount of salt in the water. Salt in water and in

soil can reduce the availability of crops to water. We measure salinity with the


electrical conductivity and the Total Dissolved Solids (TDS). TDS levels below

700mg/L and SAR (Sodium Absorption Ratio), below 4 are considered safe. TDS

levels between 700mg/L and 1750mg/L and SAR levels between 4 and 9 are

considered possibly safe and levels above these are considered hazardous to

any crop. Some crops are more sensitive to salinity than others.

The presence of salts affects plant growth in three ways:

Osmotic affects (by the total dissolved salt)

Specific ion toxicity (concentration of individual ions)

Soil particle dispersion (when the sodium is high and the salinity low)

Salinity is expressed in milligrams per liter (mg/l) of total dissolved solids (TDS).

Salinity of wastewater is generally 200-400 mg/l higher than the salinity of

freshwater supplied to a city. Industrial use of water-softening processes can

significantly increase these values if the raw effluent is discharged into the

municipal sewer.


Table 6-3: Basic features of some selected irrigation systemsIrrigation method

Topography Crops Remarks

Widely spaced borders

Land slopes capable of being graded to less than 1 % slope and preferably 0.2%

Alfalfa and other deep rooted close-growing crops and orchards

The most desirable surface method for irrigating close-growing crops where topographical conditions are favourable. Even grade in the direction of irrigation is required on flat land and is desirable but not essential on slopes of more than 0.5%. Grade changes should be slight and reverse grades must be avoided. Cross slops is permissible when confined to differences in elevation between border strips of 6-9 cm. Water application efficiency 45-60%.

Graded contour furrows

Variable land slopes of 2-25% but preferable less

Row crops and fruit

Especially adapted to row crops on steep land, though hazardous due to possible erosion from heavy rainfall. Unsuitable for rodent-infested fields or soils that crack excessively. Actual grade in the direction of irrigation 0.5-1.5%. No grading required beyond filling gullies and removal of abrupt ridges. Water application efficiency 50-65%.

Rectangular checks (levees)

Land slopes capable of being graded so single or multiple tree basins will be levelled within 6 cm

Orchard Especially adapted to soils that has either a relatively high or low water intake rate. May require considerable grading. Water application efficiency 40-60%.

Sub-irrigation

Smooth-flat Shallow rooted crops such as potatoes or grass

Requires a water table, very permeable subsoil conditions and precise levelling. Very few areas adapted to this method. Water application efficiency 50-70%.

Sprinkler Undulating 1-35% slope All crops High operation and maintenance costs. Good for rough or very sandy lands in areas of high production and good markets. Good method where power costs are low. May be the only practical method in areas of steep or rough topography. Good for high rainfall areas where only a small supplementary water supply is needed. Water application efficiency 60-70 %.

Localized (drip, trickle, etc.)

Any topographic condition suitable for row crop farming

Row crops or fruit

Perforated pipe on the soil surface drips water at base of individual vegetable plants or around fruit trees. Has been successfully used in Israel with saline irrigation water. Still in development stage. Water application efficiency 75-85 %.

Source: FAO, 1988

Table 6-4: Evaluation of common irrigation methods in relation to the use of treated wastewater Parameters of evaluation Furrow irrigation Sprinkler irrigation Drip irrigationFoliar wetting and consequent leaf damage resulting in poor yield

No foliar injury as the crop is planted on the ridge

Severe leaf damage can occur resulting in significant yield loss

No foliar injury occurs under this method of irrigation

Salt accumulation in the root zone with repeated application

Salts tend to accumulate in the ridge which could harm the crop

Salt movement is downwards and root zone is not likely to accumulate salts

Salt movement is radial along the direction of water movement. A salt wedge is formed between drip points

Ability to maintain high soil water potential

Plants may be subject to stress between irrigations

Not possible to maintain high soil water potential throughout the growing season

Possible to maintain high soil water potential throughout the growing season and minimise the effect of salinity

Suitability to handle brackish wastewater without significant yield loss

Fair to medium. With good management and drainage acceptable yields are possible

Poor to fair. Most crops suffer from leaf damage and yield is low

Excellent to good. Almost all crops can be grown with very little reduction in yield

Source: Kandiah,1990a


6.3.2 Specific Ion toxicity

Specific Ion toxicity is referred when the growth of the crop is due to excessive

concentrations of specific ions. The ions of most concern are sodium, chloride

and boron. The most prevalent toxicity from the use of reclaimed water is from

boron (household detergents or discharges from industrial plants). For sensitive

crops Specific Ion toxicity is difficult to correct short of changing the crop or the

water source. The problem is also accentuated by hot and dry climatic conditions

due to high evapotranspiration rates.

6.3.3 Water infiltration rate.

If the infiltration rate is greatly reduced it may be impossible to supply the crop or

landscape plant with enough water for good growth. In addition water irrigation

systems are often located on less desirable soils or soils having management

problems.

6.3.4 Other problems

Clogging problems with sprinkler and drip irrigation systems because biological

growth in the sprinkler head, emitter orifice, or supply line causes plugging as do

heavy concentrations of algae and suspended solids. The most frequent clogging

problems occur with drip irrigation systems. These systems are often considered

ideal because they are totally enclosed minimizing the problems of worker

exposure.

In water that is chlorinated when chlorine residuals is in excess of 5mg/L can

cause severe plant damage when the water is sprayed directly on foliage.

Distributing treated wastewater evenly over a field is the purpose of the irrigation

system. A variety of system types and components are available.

The nutrients, trace elements, and other salts contained in wastewater effluent

may occasionally reach levels that are detrimental to crops or soils. In such


cases, alternative crops must be selected or dilution water added, and these

measures may decrease the economic benefits.

Nutrients provide fertilizer value for the crop production. When nutrients are in

excess of plant needs may cause problems. The most important nutrients are: N,

P, K, Zn, B and S. Nitrogen is the most excessive in reclaimed water. Excessive

nitrogen in the latter part of the growing period may be detrimental to many

crops, causing excessive vegetative growth, delayed or uneven maturity or

reduced crop quality.

The water and nitrogen requirements of a plant vary independently during the

growing season. Thus, if wastewater containing high levels of nitrogen is applied

according to the crop's water requirements, then the amount of nitrogen applied

may exceed the crop's nitrogen requirements.

Table 6-5: Tolerance of selected crops to total dissolved solids in irrigation water, as determined by research in California, U.S.ADegree of tolerance

Fruits and berries Vegetables Field crops Forages

Not tolerantECw <0.7TDS<500

Strawberry, Raspberry Bean Carrot Bean

Slightly tolerantECw <1.2TDS<800

Boysenberry, CurrantBlackberry, Gooseberry, Plum, Grape, Apricot, Peach, Pear, Cherry, Apple

Onion, Parsnip, Radish, Pea, Pumkin, Lettuce, Pepper, Muskmelon, Sweet Potato, Sweet corn, Celery, Cabbage, Kohlrabi, Cauliflower

Cowpea, BroadbeanFlax, SunflowerCorn

Clover(alsike,ladino red and strawberry), Berseen clover, Forage corn

Moderately tolerantECw <2.2TDS<1500

Spinach, Cantaloupe, Cucumber, Tomato, Squash, Brussel, Sprout, Broccoli, Turnip

Brome,smooth Alfafa, Big trefoil, Beardless, Wildrye, Vetch, Timothy, Crested wheatgrass

TolerantECw <3.6TDS<2500

Beet, ZucchiniRape, Sorghum

Oat hay, Wheat hayBrome, Mountain, Tall fescue, Sweet clover, Reed Canarygrass Birdsfoot, Trefoil, Perennial, Ryegrass

Very tolerantECw <5.0TDS<3500

Asparagus Soybean, SafflowerOats, Rye Wheat, Sugar beet, Barley

Barley hay Tall, wheatgrass

Source: Canadian Council of Ministers of the Environment, 1987


This excess nitrogen may have the following detrimental effects:

excessive leaf growth leading to plant lodging (bending due to weakening of

plant cellulose tissue) and a decrease in the economic value of certain crops

(such as cotton, tomatoes, and fruit trees)

accumulation of high levels of nitrogen in the plants, where nitrate could

transform into nitrite- a form of nitrogen toxic to animals

groundwater contamination with percolating nitrogen in the form of nitrates.

Heavy metals in wastewater could be present at levels that affect the agriculture.

In this respect, two elements, boron and molybdenum, are often of particular

concern in wastewater irrigation schemes (Bouwer and Idelovitch, 1987). Boron

in wastewater can be toxic to plants and molybdenum can accumulate in forage

crops to levels that are toxic to these crops. Other elements could also present a

risk if industrial wastes are discharged into the municipal sewers. This is often the

case in developing countries, where even small-sized factories or craft shops

could significantly contaminate the wastewater flow. In that case, the wastewater

should be tested for chemicals that are used by the industries, as well as for

boron and molybdenum.

6.4 Steps to improve irrigation efficiency

reduce seepage losses in channels by lining them or using closed conduits;

reduce evaporation by avoiding mid-day irrigation and using under-canoby

rather than overhead sprinkling;

avoid overirrigation;

control weeds on inter-row strips and keep them dry;

plant and harvest at optimal times;and

Irrigate frequently with just the right amound of water to avoid crop distress ,

(FAO, 2001).


6.5 Suitability of irrigation methods

The suitability of irrigation methods depends mainly on these factors (Pescod,

1992):

Quality of water to be used (e.g. in case of treated wastewater SS and BOD

are taken into account)

natural conditions

type of crop

type of technology

previous experience with irrigation

required labour inputs

6.5.1 Natural conditions

The natural conditions such as soil type, slope, climate, water quality and

availability, have the following impact on the choice of an irrigation method, and

are presented in Table 6-6.

6.5.2 Type of crop

Surface irrigation can be used for all types of crops. Sprinkler and drip irrigation,

because of their high capital investment per hectare, are mostly used for high

value cash crops, such as vegetables and fruit trees. They are seldom used for

the lower value staple crops.

Drip irrigation is suited to irrigating individual plants or trees or row crops such as

vegetables and sugarcane. It is not suitable for close growing crops (e.g. rice).

6.5.3 Type of technology

The type of technology affects the choice of irrigation method. In general, drip

and sprinkler irrigation are technically more complicated methods.

Surface irrigation systems usually require less sophisticated equipment for both

constructions and maintenance (unless pumps are used).


6.5.4 Previous experience with irrigation

The choice of an irrigation method also depends on the irrigation tradition within

the region or country. The servicing maintenance of the equipment may be

problematic and the costs may be high compared maintenance to the benefits.

Often it will be easier to improve the traditional irrigation method than to introduce

a totally new method.

6.5.5 Required labour inputs

Surface irrigation often requires a much higher labour input - for construction,

operation and maintenance - than sprinkler or drip irrigation. Surface irrigation

requires accurate land levelling, regular maintenance and a high level of farmers'

organization to operate the system. Sprinkler and drip irrigation require little land

levelling; system operation and maintenance are less labour-intensive.

Table 6-6: Natural conditions and the choice of irrigation typeSoil type Sandy soils have a low water storage capacity and a high infiltration rate. They

therefore need frequent but small irrigation applications, in particular when the sandy soil is also shallow. Under these circumstances, sprinkler or drip irrigation are more suitable than surface irrigation. On loam or clay soils all three irrigation methods can be used, but surface irrigation is more commonly found. Clay soils with low infiltration rates are ideally suited to surface irrigation.When a variety of different soil types is found within one irrigation scheme, sprinkler or drip irrigation are recommended as they will ensure a more even water distribution.

Slope Sprinkler or drip irrigation are preferred above surface irrigation on steeper or unevenly sloping lands as they require little or no land levelling. An exception is rice grown on terraces on sloping lands.

Climate Strong wind can disturb the spraying of water from sprinklers. Under very windy conditions, drip or surface irrigation methods are preferred. In areas of supplementary irrigation, sprinkler or drip irrigation may be more suitable than surface irrigation because of their flexibility and adaptability to varying irrigation demands on the farm.

Water availability

Water application efficiency is generally higher with sprinkler and drip irrigation than surface irrigation and so these methods are preferred when water is in short supply. However, it must be remembered that efficiency is just as much a function of the irrigator as the method used.

Water quality

Surface irrigation is preferred if the irrigation water contains much sediment. The sediments may clog the drip or sprinkler irrigation systems.If the irrigation water contains dissolved salts, drip irrigation is particularly suitable, as less water is applied to the soil than with surface methods.Sprinkler systems are more efficient that surface irrigation methods in leaching out salts.

Source: Pescod, 1987

6.6 Selection between Basin, Furrow or Flood Irrigation


It is not possible to give specific guidelines leading to a single best solution; each

option has its advantages and disadvantages. Factors to be taken into account

include (Pescod, 1992):

Land Characteristics (slope, soil type)

Type of crop

Required depth of irrigation application

Level of technology

Previous experience with irrigation

Required labour inputs.

In Table 6-6 the choice of irrigation type is shown according to natural conditions.

6.6.1 Land Characteristics

Flat lands, with a slope of 0.1% or less, are best suited for basin irrigation: little

land levelling will be required. If the slope is more than 1%, terraces can be

constructed. Furrow irrigation can be used on flat land (short, near horizontal

furrows), and on mildly sloping land with a slope of maximum 0.5%. On steeper

sloping land, contour furrows can be used up to a maximum land slope of 3%. A

minimum slope of 0.05% is recommended to assist drainage.

Table 6-7: Selection of an irrigation method based on the depth of the net irrigation applicationSoil type

Rooting depth of the crop

Net irrigation depth per application (mm) Irrigation method

Sand shallow 20-30 short furrowsmedium 30-40 medium furrows

deep 40-50 long furrows, small basins Loam shallow 30-40 medium furrows

medium 40-50 long furrows, small basins deep 50-60 medium basins

Clay shallow 40-50 long furrows, small basins medium 50-60 medium basins

deep 60-70 large basins Source: Pescod, 1987

Surface irrigation may be difficult to use on irregular slopes as considerable land

levelling may be required to achieve the required land gradients. All soil types,

except coarse sand with an infiltration rate of more than 30 mm/hour, can be

used for surface irrigation. If the infiltration rate is higher than 30 mm/hour,


sprinkler or drip irrigation should be used. Table 6-7 a selection of irrigation

method is made based on the depth of the net irrigation application.

6.6.2 Type of crop

Paddy rice is always grown in basins. Many other crops can also be grown in

basins: e.g. maize, sorghum, trees, etc. Those crops that cannot stand a very wet

soil for more than 12-24 hours should not be grown in basins.

Furrow irrigation is best used for irrigating row crops such as maize, vegetables

and trees. Border irrigation is particularly suitable for close growing crops such

as alfalfa, but border irrigation can also be used for row crops and trees.

6.6.3 Required depth of irrigation application

When the irrigation schedule has been determined it is known how much water

(in mm) has to be given per irrigation application. It must be checked that this

amount can indeed be given, with the irrigation method under consideration.

Field experience has shown that most water can be applied per irrigation

application when using basin irrigation, less with border irrigation and least with

furrow irrigation. In practice, in small-scale irrigation projects, usually 40-70 mm

of water are applied in basin irrigation, 30-60 mm in border irrigation and 20-50

mm in furrow irrigation. In large-scale irrigation projects, the amounts of water

applied may be much higher.

This means that if only little water is to be applied per application, e.g. on sandy

soils and a shallow rooting crop, furrow irrigation would be most appropriate.

(However, none of the surface irrigation methods can be used if the sand is very

coarse, i.e. if the infiltration rate is more than 30 mm/hour.) If, on the other hand,

a large amount of irrigation water is to be applied per application, e.g. on a clay

soil and with a deep rooting crop, border or basin irrigation would be more

appropriate.


The above considerations have been summarized in Table 6-7. The net irrigation

application values used are only a rough guide. They result from a combination

of soil type and rooting depth. For example: if the soil is sandy and the rooting

depth of the crop is medium, it is estimated that the net depth of each irrigation

application will be in the order of 35 mm. The last column indicates which

irrigation method is most suitable.

6.6.4 Level of Technology

Basin irrigation is the simplest of the surface irrigation methods. Especially if the

basins are small, they can be constructed by hand or animal traction. Their

operation and maintenance is simple. Furrow irrigation - with the possible

exception of short, level furrows -requires accurate field grading. This is often

done by machines. The maintenance - ploughing and furrowing - is also often

done by machines. This requires skill, organization and frequently the use of

foreign currency for fuel, equipment and spare parts. Short, level furrows - also

called furrow basins - can, like basins, be constructed and maintained by hand.

6.6.5 Previous experience with irrigation

The smaller the basins, the easier their construction, operation and maintenance.

If irrigation is used traditionally, it is usually simpler to improve the traditional

irrigation method than it is to introduce a previously unknown method.

6.6.6 Required labour inputs

The required labour inputs for construction and maintenance depend heavily on

the extent to which machinery is used.

In general it can be stated that to operate the system, basin irrigation requires the

least labour and the least skill. For the operation of furrow and border irrigation

systems more labour is required combined with more skill.


7. Storage of water (reservoirs)

7.1 The need for storage

Reservoirs are those water bodies formed or modified by human activity for

specific purposes, in order to provide a reliable and controllable resource.

Storing water during a wet year for use in a dry year, or during spring snowmelt

for use during the summer, or other low flow times of the year, can help meet the

demand for water. Irrigated agriculture requires water in the summer and early

fall. Their main uses of storage include:

drinking and municipal water supply,

industrial and cooling water supply,

power generation,

agricultural irrigation,

river regulation and flood control,

commercial and recreational fisheries,

body contact recreation, boating, and other aesthetic recreational uses,

navigation,

canalisation, and

waste disposal (in some situations).

The main categories of storage include ground storage and elevated storage.

Ground storage tanks or reservoirs can be below ground, partially below ground,

or constructed above ground level in the distribution system and may

accompanied by pump stations if not built at elevations providing the required

system pressure by gravity. Ground storage reservoirs can be either covered or

uncovered. Covered reservoirs may have concrete, structural metal, or flexible

covers. Reservoirs are usually found in areas of water scarcity or excess, or

where there are agricultural or technological reasons to have a controlled water

facility. Where water is scarce, for example, reservoirs are mainly used to

conserve available water for use during those periods in which it is most needed


for irrigation or drinking water supply. When excess water may be the problem,

then a reservoir can be used for flood control to prevent downstream areas from

being inundated during periods of upstream rainfall or snow-melt. Particular

activities such as power generation, fish-farming, paddy-field management or

general wet-land formation, for example, are also met by constructing reservoirs.

By implication, they are also water bodies which are potentially subject to

significant human control, in addition to any other impact. Reservoirs are,

nonetheless, a considerable, frequently undervalued, water resource:

approximately 25 per cent of all waters flowing to the oceans have previously

been impounded in reservoirs (UNEP, 1991).

Reservoirs range in size from pond-like to large lakes, but in relation to natural

lakes the range of reservoir types and morphological variation is generally much

greater. For example, the most regular, and the most irregular, water bodies are

likely to be reservoirs. This variability in reservoirs, allied to management

intervention, ensures that their water quality and process behaviour is even more

variable than may be characterised as normal. As reservoirs are so variable, it

can often be misleading to make any general statements about them without

significant qualification as to their type.

Generally, all reservoirs are subject to water quality requirements in relation to a

variety of human uses. The variation in design and operation of control structures

in reservoirs can provide greater flexibility and potential for human intervention

than in natural lakes (and, therefore, considerable scope for management and

control) with the objective of achieving a desired water quality.

Water is storaged for reuse for two main reasons:

To release effluents at the time of the year that it is desired (controlled

discharge).

To manage to have a more good quality of effluents (wastewater treatment).


Wastewater storage reservoirs add flexibility to the operation of the system,

optimize the reuse of reclaimed water, increase the area which can be irrigated

and release effluents of a better quality.

Because of the high quality of effluent that is required for certain types of crops,

stabilization reservoirs are able to remove many of the contents of wastewater,

(organic matter, pathogens, heavy metals, hard detergents, pesticides, organic

micro-pollutant and other pollutants) which are not removed with the classical

methods of sewage treatment.

Demands for reclaimed water vary seasonable with higher demands during

summer months and lower demands during winter months. To storage large

amounts of water this would require construction of a dam and large reservoir.

Open reservoirs are more economically when we consider the size of the

reservoirs. In a high developed area large reservoir would be difficult and the

cost of doing such a storage facility and the associated pumping, pipelines, land

expenses make seasonal storage option cost prohibitive (Asano, 2002).

According to Asano, (2002) long term storage difficulties for reclaimed water are:

Algae growth and suspended solids from open reservoirs are a source of

clogging the sprinkler system. All irrigation water must be filtered when enters

the distribution system from open reservoirs.

Aesthetic-excessive algae growth may have difficulties in degradation in both

appearance and increased odor.

Functional-where quality degradation may result operational difficulties in

downstream irrigation system (Asano, 2002). Storage is required to hold

water for peak demand months. The amound needed is the total of monthly

differences between supply and demand.

Covered storage in ground is used for unrestricted urban reuse where aesthetic

considerations are important. Ponds are less costly and require more land per


gallon stored. Covered storage is preferred to preclude biological growth and

maintain chlorine residual. To calculate the required usable storage we use the

irrigation demands that occur at night time peak hour and maximum day

demands.

Stabilization reservoirs are another category of reservoirs. They have been

operated for many years to a lot of countries and the main scope of their use was

to storage and treats the wastewater effluents during the wet winter months. The

reclaimed water from the reservoirs is used for agriculture irrigation during the dry

summer months. Stabilization reservoirs as they are designed nowadays are able

to remove BOD, COD, detergents and other pollutants.

There are insufficient field data available to formulate an adequate design

criterion for storage reservoirs, but pathogen removal depends on retention time

and on the possibility of having the reservoir divided into compartments. The

greater the retention time and the larger the number of compartments in series,

the higher the efficiency is the pathogen removal. A design recommendation,

based particularly on data available from natural storage reservoirs operating in

the Mesquital Valley, Mexico, is to provide a minimum hydraulic average

retention time of 10 days, and to assume two orders of magnitude reduction in

both faecal coliform and helminth eggs. Thus, the stored wastewater should

contain no more than 102 eggs per litre and not more than 105 faecal coliform per

100 ml, in order that the WHO guidelines for unrestricted irrigation are attained

(Asano, 2002).

The benefits of water storage must be carefully weighed against the costs and

impacts. Some of the benefits include:

Storing water makes it available for use when it may not otherwise have been

available

Storage can reduce the risk of water shortage to certain water users

Storage can increase the number of industries and irrigators using water in a

given watershed


Storage can increase the economic production generated by the use of water

7.2 Health impacts associated with storage reservoirs

Various potential health impacts have been associated with the chemical,

microbiological and physical issues identified in Table 7-1. Excessive water age

in many storage facilities is the most important factor related to water quality

deterioration. Long detention times in the reservoir might result to microbial

growth and chemical changes. The excess water age is caused by:

Water that is not cycled through the facility.

Short circuiting within the reservoir.

Table 7-1: Water quality problems associated with storage water facilitiesChemical Issues Biological Issues Physical IssuesDisinfectant Decay Microbial Regrowth* CorrosionChemical contaminants* Nitrification* Temperature/StratificationDBP formation Pathogen contamination* SedimentTaste and odors Tastes and odors*water quality problem with direct potencial health impactSource: Metcalf and Eddy, 2003

Chemical problems contain (Metcalf and Eddy, 2003):

the development of taste and odor,

loss of disinfectant residual,

increase in pH,

corrosion, and occurrence of hydrogen sulphide,

buildup of iron and manganese

leachate from coatings and formation of disinfection by-products.

7.2.1 Loss of disinfectant residual

It is a result of the decrease of free chlorine or total chlorine. This loss can be

affected by sun light, temperature, microbiological activity, nitrification, organic

and inorganic compounds presented. A long detention time allows the

disinfectant residual to be completely depleted for that reason the water is not

protected by microbial regrowth.


7.2.2 Increase in pH

When pH is stable is essential for the quality of the water. Rechlorination can

change pH either down or up (depending on the chemicals used). New concrete

storage tanks can increase pH of water because of its contact with walls and

floor. The longer the water stays in the reservoirs the pH is more increased.

7.2.3 Corrosion and occurrence of hydrogen sulphide

If the water is reddish there may be a problem with iron uptake from the metal

surfaces that is in contact. How red is the water depends from pH, alkalinity,

temperature of water, if there is proper cathodic protection, from the coatings,

and from the water flow. For bringing water to its natural colour may require

inspection and maintenance of the storage tank.

Hydrogen Sulphide is a gas with an aesthetic concern because of its egg odor. It

is present under the following conditions (Asano, 2002):

high levels of sulphate ions,

sulphate-reducing bacteria,

excess electrons,

low or no dissolved oxygen.

7.2.4 Iron and Manganese.

They can enter the reservoir where it resettles. To prevent the metals from

affecting the quality of water, a reqularly cleaning program can remove sediment

from storage facilities.

7.3 Microbiological Problems

Microorganisms can enter from outside sources such as uncovered reservoirs.

Bacteria growth is common to tank surfaces and in other non circulating zones of

a tank. Microorganisms multiply with long water-detection times, warm

temperatures, and adequate nutrient levels. Organic paints and coatings

because they can support bacterial growth this leads to biocorrrosion of the

structure of the reservoir or to increase the porosity of the walls and this creates


spaces for the bacteria to grow. Worms and insects also can enter from

connections, dead-ends. If the storage reservoir does not have secured insect

screening they can enter easily to water.

7.4 Physical problems

7.4.1 Sediment buildup

Sediment accumulates in storage tanks where the velocity is minimal. It is an

important factor of water quality. Water quality problems associated with

sediment include increased disinfectant demand, microbial growth, disinfection

by-product formation, and increased turbidity within the water. Cleaning the

reservoir can help minimize sediment builtup.

7.4.2 Contaminants

Usually the open reservoirs provide a large opportunity for entry of contaminants.

Bird droppings and animal excrement can cause contamination to water and also

can transmit many diseases to water. Organic matter also such as leaves is a

concern of open reservoirs. In December 1993, a Salmonella typhimurium

outbreak in Gibeon, Missouri resulted from bird contamination in a covered water

storage tank (Clark et al., 1996).

7.4.3 Temperature

It plays an important role to the quality of water and changes the storage

facilities.

7.5 Open and enclosed reservoirs

7.5.1 Storage reservoirs open and closed

They are made of steel, reinforced concrete and plastic lined ponds and

materials used. In both reservoirs depth to surface ratio are important in water

quality.Shallow open reservoirs have problems such as algae, aesthetic

problems, clogging of irrigation emitters. When the ratio depth to surface is that


the surface area is not large enough the water may cause anaerobic bacteria and

create sludge at the bottom of reservoir. The sludge can cause turbidity problems

because of hydrogen sulphide (odor problems). To closed reservoirs the ratio

should allow turnover the volume of reservoir.

7.5.2 Inlet/Outlet Designs

Inlet/Outlet should be designed at opposite ends so that the right flow can

achieve. Anaerobic bacteria can thrive when leaving open areas.

7.6 Problems with storage open reservoirs

The principal problems with the storage in open reservoirs are (Metcalf and Eddy,

2003):

Release of odors, principally hydrogen sulphide

Temperature stratification

Loss of chlorine residual

Low dissolved oxygen resulting in odors and fish kills

Excessive growth of algae and phytoplankton

High levels of turbidity and color

Regrowth of microorganisms

Water quality deterioration due to bird and rodent populations

The production of hydrogen sulphide odors is related from the stratification of the

reservoir caused by the temperature differences. In Tables 7-2 and 7-3 problems

in the operation of open reservoirs and manegement strategies are shown.

Table 7-2: Problems in the operation of open reservoirs used for the storage of reclaimed water Reservoir problem Descripton

Physical/aesthetic:Colour The presense of colour can affect the aesthetic acceptance of the water.Often caused

by the presence of humic materials and fine silts and clays in runoff and the presence of colour in the reclaimed water

Odors (primarily H2S ) One of the most common problems encountered with the storage of reclaimed water.In addition to causing odors, H2S has a chlorine demand.


Temperature Water may be unusable during certain times of the yearTemperature stratification

Usually occurs once or twice a year depending on the latitude

Turbidity The presence of turbidity can affect the aesthetic acceptance of the water.Turbidity can be caused by runoff containing silt and clay and by algal growth.

Chemical:Chlorine Chlorine and compounds containing chlorine may be toxic to aquatic life in open

reservoirs Dissolved oxygen Low DO can cause fish kills and allow the release of odors in open reservoirsNitrogen Nutrient capable of stimulating phytoplanktonPhosphorus Nutrient capable of stimulating phytoplanktonBiological:Algae Presence of excess algae can cause odors,increase turbidity,and clog filtersAquatic foul The presence of excessive numbers of aquatic birds can degrade the water quality of

the stored waterBacteria Regrowth is a common occurrence in open storage reservoirs. May affects possible

applications.Chlorophyll Presence of excess algae and plant matterHelminths May affect possible reuse applicationsInsects(mosquitoes) May require spraying of insecticidesPhytoplankton Presence of excess algae can cause odors increase turbidity,and clog filtersProtozoa May affect possible reuse applicationsViruses May affect possible reuse applications


Table 7-3: Management strategies for open reservoirs used for the storage of reclaimed waterManagement strategies

CommentsOpen storage reservoirs

Aeration/destratification Installation of aeration facilities can be used to maintain aerobic conditions and eliminate thermal stratification.May result in release of phosphorus from bottom sediments

Alum precipitation Alum precipitation has been used to remove suspended solids and phosphorus. Can be used to stop release of phosphorus from sediments

Biomanipulation Control of microorganism growth ratesCopper sulphate addition

Copper sulphate is applied to control the growth of algae.The use of copper may be eliminated because of toxicity concerns over accumulation of copper

Destratification (including recirculation)

Submerged or aspirating mixers can be used to eliminate thermal stratification. Recirculating pumps can also be used.May result in release of phosphorus from bottom sediments

Dilution Water from other sources can be blended with water from the storage reservoir to manage the water quality

Dredging Accumulated sediment can be removed annually to limit the formation of deposits and the generation of hydrogen sulfide

Filtration Water from the storage reservoir can be filtered through a rock filter, a slow sand filter or a disk –type filter to remove algae and to improve the clarity of the water

Natural microorganism decay

The effectiveness of natural decay will depend on the operation of the reservoir and the detenton time

Nutrient removal Removal of nutrients (e.g., nitrogen and phosphorus) to control aquatic growthsPhotooxidaton With proper mixing, advantage can be taken of the beneficial effects of exposing the water to sunlightWetlands treatment Water from the storage reservoir can be passed through a constructed wetland to improve the clarity of

the effluent and to remove algaeWithdrawal from selected depths

Varying water quality can be obtained by drawing off water at selected depths within the reservoir


7.7 Guidelines for avoiding problems in enclosed reservoirs

According with Metcalf and Eddy, (2003) the problems which are related with the

enclosed reservoirs are:


Stagnation

Release of odors, (hydrogen sulphide)

Loss of chlorine residual (slower than the open reservoirs)

Regrowth of microorganisms

The growth of plakton in reservoirs can be controlled using copper sulphate or

more selective algaecides. The use of chlorine in open reservoirs is not

recommended as a control measure. When the number of the organisms starts to

increase rapidly chemicals should be applied. Treatment may be needed when

the number of the organisms exceeds 500 to 1000 units per millilitre.

Excessive algae growth could cause aesthetic, water quality and other problems,

including: turbidity, odors, increase of maintenance work due to developing free-

floating organisms that may attach to the structures and escape into the

distribution system.

Algae are commonly controlled in reservoirs with (Metcalf and Eddy, 2003):

Aerators

Addition of chlorine and /or copper sulphate. These chemicals are not always

effective.

A natural algaecide

A cartridge filter installed at the effluent of reservoirs to remove algae

upstream of the distribution system.

Reservoirs however are occasionally taken out of service for inspection, cleaning,

repairs and painting. When the reservoir is dry it must be scraped and the

sediment and any plant material must be removed to a landfill or applied as a soil

to agriculture (fodder crops). Disking the bottom sediment lets the accumulated

organic matter and nutrients. In Table 7-4 and 7-5 problems in the operation and

management strategies for enclosed reservoirs are shown.


Table 7-4: Management strategies for enclosed reservoirs used for the storage of reclaimed waterManagement strategies Comments

Enclosed storage reservoirsAeration Maintain residual level of DO to eliminate the formation of odorsChlorination Used to control the growth of microorganismsRecirculaton Adequate recirculation can limit the growth of microorganisms and the

formation of odorsSource: Metcalf and Eddy, 2003

Table 7- 5: Problems in the operation of enclosed reservoirs used for the storage of reclaimed water

Reservoir problem DescriptonPhysical/aesthetic:Colour Often caused by the presence of humic materials in reclaimed water Odors (primarily H2S ) One of the most common problems encountered with the storage of reclaimed

water.In addition to causing odors, H2S has a chlorine demandTurbidity The presence of turbidity can affect the aesthetic acceptance of the waterChemical:Chlorine Chlorine and compounds containing chlorine may cause odors.Chlorine is used

commonly to controlbiological growths Dissolved oxygen Lack of oxygen can lead to the release of odors in enclosed reservoirs Biological:Bacteria Regrowth has occurred in enclosed storage reservoirs.May affect possible

applicationsInsects(mosquitoes) Insects can enter improperly sealed reservoirs.May require spraying of

insecticidesViruses May affect possible reuse applicationsSource: Metcalf and Eddy, 2003

7.8 Disinfection of tanks

The chemicals used for disinfection of tanks are the same as those used for

disinfection of pipelines. Numerous disinfection chemicals are available. The

following three are used most commonly:

Liquid chlorine (Cl2) is inexpensive but highly toxic and should be used only

by appropriately trained individuals with the proper chlorinators and ejectors

Sodium hypochlorite (NaOCl) which is liquid stored in glass, rubber-lined, or

plastic containers of varying sizes. It is more expensive and bulky than liquid

chlorine, but is much safer to handle

Calcium hypochlorite Ca(OCl)2 which is approximately 65 percent chlorine by

weight. It is easy to handle in either tablets or granular form, but is relatively

expensive and must be kept dry to prevent degradation. All tods and

equipment are removed from the tank, and the tank is washed, swept, or

scrubbed to remove any debris or dirt.


7.8.1 Reservoir maintenance and inspections

It can be divided to maintenance planning which includes preventive and

predictive activities and emergency maintenance. Preventive activities are made

to extent the life prevent failure of structures and equipment and preclude water

quality problems. Predictive activities include the use of technology and methods

to collect and analyse data to identify present conditions, forecast failure.

Emergency maintenance is unplanned and is performed as a result of a natural

disaster.

Maintenance activities include cleaning, painting and repairing of structures

coatings and linings are very important for the protection and long life of

structures and of caurse to water quality. Special precautions should be used

when selecting coatings, surface preparation and curing conditions. Most

cleaning procedures have regular cleaning programs and have an interval

between 2 and 5 years. Kirmeyer et al (1999) suggests that covered facilities

must be cleaned a minimum of every 3 to 5 years or more often if needed on the

basis of inspections and water-quality monitoring.

Open and closed reservoirs require more usually cleaning. They may require

cleaning every 3 to 5 times. This depends from the built up of sludge on the

bottom. Sludge is removed through pumping of flushing so it’s important to

provide access. In open reservoirs dredging of the material from the bottom need

to be included in the design. Inspection of the reservoir is needed and it depends

from the type of storage, from its age and condition, from the time since the last

cleaning or maintenance, and its history of water quality. Inspections (periodic)

may require climbing the tank and may conducted every 3 to 4 months.

7.8.2 Other useful points in storage tanks

7.8.2.1 Altitude Valves


Altitude Valves are used to prevent tanks from overflowing by shutting off inflow

to the tank when the water level in the tank approaches a high level. These

valves are located at the base of the tank.

7.6.8.2 Cathodic Protection and Coatings The presense of air and water in the tanks might cause the tank corrode rapidly if

they are not properly protected. Different types of paints and coatings are

required for the interior and exterior of the tanks. There must be a good

inspection of the paintings to prevent failure of the coatings. Most tanks are

equipped with cathodic protection systems that protect further more the metal on

the inside of the tank.

7.6.8.3 Overflows and VentsTanks should have an overflow pipe that must be able to handle the maximum

potencial overflow volume of the tank. The pipe should have an air gap at its

discharge and a check valve that can prevent the birds and insects from entering

the pipe. The draining and filling of tanks also requires a large volume of air

enters and leaves the tank during each cycle. The vents should be screened to

prevent birds and insects from entering the tank. Also specific design is needed

in cold climates from preventing the block of the vent with ice (Metcalf and Eddy,

2003).


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