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1 Chapter 1 : Introduction
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
1 Introduction
1.1 Background
Constructed wetlands (CWs) have been defined as „„engineered systems, designed
and constructed to utilize the natural functions of wetland vegetation, soils and their
microbial populations to remove contaminants in surface water, groundwater or
waste streams” and which is to as nature‟s kidneys (ITRC, 2003). CWs can be used
as part of decentralized wastewater treatment systems, due to their characteristics as
low construction cost, low-technology systems, relatively low operational &
maintenance cost and requires significantly less energy. Denny et al., (1997) pointed
out that CWs are particularly suitable for developing countries as well as any rural or
low density area in the world, whereas conventional systems are appropriate in
industrialized regions and densely populated areas with guaranteed power supplies,
easily replaceable parts, and available of skilled manpower to ensure operation and
maintenance requirement.
Wolverton (1987) pointed out that the scientific basis for waste water treatment in a
vascular aquatic plant system is the cooperative growth of both the plants and the
microorganisms associated with the plants. A major part of the treatment process for
degradation of organics is attributed to the microorganisms living on and around the
plants roots. Once microorganisms are established on aquatic plants root, they form
a symbiotic relationship in most cases with the higher plants. This relationship
normally produces a synergic effects resulting in increased degradation rates and
removal of organic compounds from the wastewater surrounding the plant root
systems. Also, microorganisms can use some or all metabolites released through
plant roots as a food source. By each using the other waste products, this allows a
reaction to be sustained in favor of rapid removal of organics from wastewater.
Generally, common reed (Phragmites australis) is among the most popular plants
used in constructed wetlands because of high tolerance and abundance in several
areas of the world (Kadlec and Knight 1996).
The first experiments aimed at the possibility of wastewater treatment by wetlands
plants were undertaken by Käthe Seidel in Germany in 1957 at the Max Plank
Institute in Plön (Seidel, 1995). From 1995, Seidel carried out numerous experiments
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Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
on the use of wetland plants and especially Bulrush (Schoenoplectus = Scirpus
lacustris) for the treatment of various types of wastewater. In the mid-1960s, Seidel
began collaboration with Reinhold Kickuth from Göttingen University, but the
collaboration ended after a few years due to person reasons (Kadlec and Wallace,
2009). After then Kickuth developed a HSSF wetland process, which is also known
as root zone method (RZM). Constructed wetlands with sub-surface horizontal flow
drew more attention in Europe during the 1980s and 1990s with vertical flow and
their combination (Cooper et al., 1996; Vymazal et al., 1998). The first European
national guideline was published in Germany by ATV (Abwassertechnische
Vereinigung) in 1989 (ATV H 262, 1989) followed by European Guidelines (2008).
According to the inventory almost 3000 CWs existed in Lower Saxony in1994 and
more than 50000 small constructed wetlands were in operation by 2003 with majority
of system built to upgrade septic tank efficiency (Vymazal and Kröpfelová, 2008,
Vymazal 1998).
Similarly, CWs with sub-surface technology was started in North America during the
early 1970s. Similarly, Tanner et al. (2000) reported that many communities in New
Zealand have been using constructed wetlands as a cost effective means of
secondary and tertiary wastewater treatment. Since the mid 1980s, the concept of
using constructed wetlands has gained increasing support in Southern Africa. At
present, CWs are in operation, in Asian countries like India, China, Korea, Taiwan,
Japan, Nepal, Malaysia and Thailand for various types of waste wastewater (Kadlec
and Wallace, 2009).
CWs can be divided into two types, first is free-water surface type (FWS) in which the
water level is over the surface, and second is subsurface type (SF), in which the
water level is maintained below the surface. The subsurface can be further
categorized into two types based on the flow pattern, one with horizontal subsurface
(HSF) and another with vertical subsurface flow (VSF) (Vymazal, et. al., 2010). The
illustration of each system can be seen in the figure below. The free water surface
constructed wetlands (FWS) closely resemble natural wetlands because they look
like ponds containing aquatic plants that are rooted in the soil layer on the bottom.
The water flows through the leaves and stems of the plants. Their design and
operation is very close to pond systems.
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Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
The main focus is based on the constructed wetlands with subsurface flow. This is
due to several researches indicating that the pollutant removal efficiency is better
than in FWS per unit of land, implying the area requirement is lower. These systems
also pose no problem of mosquito or other insects breeding as well as the human,
probably children, exposure to surface wastewater. Some disadvantages of this type
are higher cost and have lower ecological value comparing to the FWS wetlands,
which are of minor concerns. The HSF and VSF systems do not resemble natural
wetlands because they have no Surface flow of water. They contain a bed of media
which is typically gravel and sand, but also soil or crushed rocks can be also used.
Within the media, emergent macrophytes are planted and the water is introduced
beneath the surface of the media and is flowing through the roots and rhizomes of
the plants. Conventionally, the flow in HSF systems is continuous, hence it creates a
“saturated” condition within the wetland body whereas the flow in VSF systems is
commonly intermittent, which results in an “unsaturated” and thus aerobic condition.
A simple and effective operation and maintenance system is essential for operating a
wastewater treatment system. Centralized wastewater management systems are
difficult to operate because of the difficulties in maintaining the long sewer networks
and treatment plant. So the constructed wetland as polishing biotopes in Gadenstedt
was constructed in 1998 as a part of decentralized waste water treatment system
covering the area of 1.1 hectare. The project„‟ Ecotechnological treatment of waste
water and sewage sludge in Lahstedt‟‟ was registered and officially sponsored project
at the world exhibition EXPO 2000 in Hanover. After achieving the good results, the
Lahstedt Municipality has decided to expand and improvement in the sewage plants
in another locality of Municipality like Oberg, Münstedt, Adenstedt, and Groß-
Lafferde. Likewise, small community of 600 residents in Berel introduced CWs
system in 2008 to ensure environment protection and better effluent quality before
discharging into the water receiving course. CWs are working as secondary
treatment plant and in the combination with pond system. The overall efficiency of
treatment plants achieved by removing 92% COD, 95% BOD, 96% NH4-N, 81% TN
and 55% TP at Gadenstedt and similarly 86 % COD, 94% BOD, 81% NH4-N, and
52% TP at Berel.
4 Chapter 1 : Introduction
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Decentralized system of treating wastewater ,with constructed wetlands, can provide
not only a more economical and energy efficient means of achieving treatment
objective , but also a resource in the form of reclaimed water available for landscape
irrigation or creation of wildlife habitats. Such an approach is more in line with the
philosophy of sustainable development and suitable technology for developing
countries.
1.2 Objectives
The objectives of this thesis were to evaluate the treatment efficiency of the
constructed wetland built in Gadenstedt and Berel. Similarly other objectives are as
follows:
Visiting in the study area.
Analysis of data of influent and effluent concentration of BOD, COD, NH4-N, TN,
TP
To study the efficiency of CWs to reduce BOD,COD,NH4-N,TN,TP
To examine the hydraulic characteristics of the flow-through system.
Economic analysis of power consumption and cost.
Evaluate the effect of influent pH and temperature effects
To focus as Constructed Wetlands are suitable technology in the context of
Nepal
1.3 Methodology
Literature Reviews Literature review is one of the most important methodologies, which helps to bring
clarity and focus in the research subjects. The literatures relevant to the study subject
were studied from available books, journals, previous thesis, reports and internet
sites to formulate the subject matter, develop conceptual study framework, select
study area, and later discuss the results. Further, before visiting field various
published/unpublished national and international reports and maps related to the
study area were collected and studied, which attributed to understand more deeply.
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Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Data collections Data collections are the secondary methodology that has been used during the
research study for this thesis. Both primary and secondary data collections have
been made.
Primary data collection: Field visit, sample taken of wastewater, direct measurement pH and temperature in
field and measurement of influent and effluent concentration of BOD, COD, NH4-N,
TN, and TP in the central Laboratory were observed and data collected. Similarly
discharge, power consumption were also collected directly in field.
Secondary data collection (Data regarding the climate and hydrology from the relevant organizations) The existing data in relevant to this thesis writing from the different organizations can
be categorized into this group. The data and information from the various
meteorological departments, research organizations come under this category. An
enormous number of such data and information have been used in this study.
Analysis, Discussion and Interpretation of the data The primary and secondary data obtained from the field and laboratory is processed
for further analysis and interpretation.
Conclusions and Recommendations Depending upon the analysis and interpretations of the data conclusions and
recommendations has been suggested for the future.
Report Writing Finally, the report is prepared after data processing and analyzing along with
evaluation and interpretation of the field data, laboratory inferences and maps. All the
results and discussion will be synthesized and presented in the reports. It is obvious
that all these stages will be carried out with the iterative and frequent consultative
approach.
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Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
1.4 Structure of Thesis
Thesis Layout This thesis, presented in ten chapters, will give more information to the reader about
the constructed wetlands of Gadenstedt and Berel. This research work is basically
concerned with the investigation of constructed wetlands, types of wetlands used for
waste water treatment, method of reduction of organic matter (BOD, COD) and
nutrients (N,P) ,types of vegetation used in the treatment plants , soil properties, and
design process of subsurface vertical flow and horizontal flow CWs. Besides, the
thesis is presenting the present scenario of wastewater treatment in Nepal and
suitability of CWs technology transfer to Nepal.
Chapter 1 presents a general introduction about the thesis, objectives of the study,
the methodology used. Chapter 2 describes an overview of Organization
involvement (Ingenieurbüro Blumberg, Wasserverband Peine, and Lahstedt
Municipality) and their responsibility. Chapter 3 discuss about wastewater treatment
through Constructed Wetlands and its importance and implication. This chapter
focuses to wastewater qualities basically chemical, physical, and Biological
characteristics and Nutrients. This chapter also provides description on treatment
requirements guidelines, types of constructed wetlands and treatment mechanism.
Chapter 4 outlines a description on the theoretical approaches and methodology of
basic design recommendation and design principle of horizontal and vertical
subsurface CWs. This chapter also indicates the soil clogging and soil aeration in
vertical flow CWs. Chapter 5 explain an overview of soil used in substrate for
wastewater treatment process in the CWs. Chapter 6 shows the scenario of
Macrophytes used and its function for the wastewater decomposition in the CWs.
Chapter 7 describes the scenario of wastewater treatment in Nepal. Chapter 8
presents a brief description of study area geography, topography; climate, hydrology
and detail about project structure of Gadenstedt and Berel. This chapter describes
also the field data analysis of BOD, COD, NH4-N, TN, and TP. Chapter 9 presents
the analysis and discussions of the results of wastewater effluent from the CWs.
Especially focus to BOD, COD, NH4-N, TN, TP, and pH and temperature analysis.
Also focus to economic analysis of power consumption in two study area and
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Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
highlighted about CWs as a suitable technology in Nepal. Chapter 10 deals the
conclusions and recommendations that have been lay out from the investigation of
result analysis of BOD, COD, N, P, pH value in concern to the improvement of CWs
efficiency.
8 Chapter 2: Organization involvement
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
2 Organization involvement
2.1 Ingenieurbüro Blumberg
Blumberg Engineers is associated with a network of consulting firms in Germany,
Europe and other countries round the world. Involvement of Ingenieurbüro Blumberg
is in planning, designing, and construction as well as monitoring and supervision of
various engineering projects of water and wastewater treatment for more than 20
years. Ingenieurbüro has experiences in the successful application of wastewater
and water treatment systems, having completed over 350 large and small scale
projects worldwide, including industrial project across several sectors over the last 20
years. They have also long experience of constructed wetlands for the wastewater
treatment of small community, industrial effluent, agricultural effluent and road run-
off. Ingenieurbüro works closely with municipalities and districts for the promotion of
wastewater treatment by constructed wetlands as an eco-technology. They are
providing consulting services in the environment sector. Especially, Ingenieurbüro
involves in monitoring and supervision as well as provides technical advice for the
betterment in the Lahstedt municipality and Berel wastewater treatment project after
the construction.
2.2 Wasserverband Peine
The Wasserverband Peine has been working in the drinking water supply and
industrial water since 1952. In 1996, Wasserverband Peine has involved in the
wastewater treatment sector and especially providing services in the region of Peine,
Baddeckenstedt, Borsum and Dransfeld. The regional office in Baddeckenstedt is
responsible for the water sample collection, analysis and data recording of Berel
wastewater treatment plant.
2.3 Lahstedt municipality
Lahstedt Municipality has given more importance on the conservation of nature and
the environment and municipality are operating „‟ community sanitation Lahstedt „‟ in
the five villages of the municipality. Municipality has their own central laboratory,
which is responsible for monitoring, water sample collection, analysis and data
recording of Gadenstedt.
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3 Wastewater treatments through the Constructed wetlands
(Literature review)
3.1 Constructed Wetlands
Constructed wetland treatment systems are engineered systems that have been
designed and constructed to utilize the natural processes involving wetland
vegetation, soils, and their associated microbial assemblages to assist in treating
wastewater (Vymazal, 1998). There are three types of wetlands categorizes
according to flow type like free water surface flow, horizontal subsurface flow and
vertical subsurface flow. They all have macrophytes coverage of varying degree and
the flow is usually driven under gravity system. In constructed wetlands, pollutants
are removed through a unique combination of physical, chemical and biological
processes, including sedimentation, precipitation, adsorption to soil particles,
assimilation by plant tissue and microbial transformations.
Bastian et al.,(1993) described that constructed wetlands have been designed not
only for the single purpose of treating wastewater but also implemented for multi use
objective such as treated wastewater effluent using as a water source for creation
and restoration of wetland habits for wildlife and environmental enhancement. The
efficiency of CWS for the pollutants removable is largely depends upon the bed size,
composition of substrate, type of vegetation, flow pattern, environmental conditions
and wastewater composition. The degree of control is larger than in a natural wetland
where species composition and performance may change over time. The treatment
methods by CWs were developed in Germany in 1952 at the Max Planck Institute in
Plön (Seidel 1995) and in the mid-1980 in Europe (Copper, 1996).
CWs are suitable to treat the wastewater coming from single house, small
community, as well as industrial effluent; land fill leachate, agricultural effluent and
road run-off. A relatively large amount of treatment plants are currently in use in
Europe and North America. Most of them are small, but for example in Denmark,
where the total amount is about 100 plants, there are more than 30 plants
constructed for 5 000-6 000 person equivalents (Leonardson, 1994).
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Due to simple construction, low cost and large buffering capacity, CWs with
subsurface flow have been constructed in Africa, Asia, and South America.
3.1.1 Application and Importance of Constructed Wetlands
Constructed wetlands are an appropriate technology for small communities in rural
and suburban areas. Many rural projects with activated sludge plants failed because
it was not properly operated, often no skilled stuff is available or the energy costs is
no longer affordable. Constructed wetlands may also be applied for primary,
secondary or tertiary treatment and may need a pre treatment before discharging into
constructed wetlands. In general, influent and effluent constitutes of these
characteristics; data shown in Table 3.1
Table 3.1: Wastewater treatment plant Shenyang (China) for 6000 people
(Source: Ingenieurbüro Blumberg, Gottingen)
CWs are used in various fields to increase the water quality and at various treatment
levels as described below.
In domestic wastewater treatment, CWs treated the disposal of single houses or
small dwelling cluster. But it required to pretreatment in the septic tanks. CWs are
mostly used as secondary treatment. In animal wastewater treatment, livestock
wastewater includes dairy manure, milk house wash water, run off from cattle
feeding, poultry and swine manure are collected and treated. The strength of
wastewater is higher than for municipal applications, with BOD, TSS and ammonia
often above 100 mg/l (Kadlec and Wallace, 2009). In mine water treatment, a large
number of treatment wetlands were built the 1980s to treat acids mine drainage in the
United States (Wieder, 1989). CWs were in used at more than 300 sites in the United
States in 1989, to increase the pH and reduce concentration of iron and /or
manganese at coal mine sites.
Industrial wastewater from food processing is containing more bio-degradable and
nitrogen. CWs are used to reduce of nutrients and organic. Application area of CWs
2006/07 Influent Parameters Effluent Parameters
COD 191.0 mg/l 11.8 mg/l
BOD5 69.63 mg/l 11.00 mg/l
NH3-N 39.2 mg/l 1.07 mg/l
Total P 4.61 mg/l 0.37 mg/l
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is now in wine, starch, alcohol, sugar and meat processing industries. Pulp and paper
mill are using CWs to reduce the effluent value in limitation. Process water and storm
water coming from petroleum refineries are being treated by constructed wetlands as
using advanced secondary and tertiary treatment (Knight et al., 1997). When the
inorganic and organic degraded water combines with the rainfall and groundwater,
then leachates are produced with more toxic and damaging surrounding
environment. In modern lined landfills, leachates are collected from the lined cells
and treated by constructed wetlands, which is one of rapidly developing technology,
with both surface flow and sub surface flow.
After the rainfall, pollutants concentration and loads are generally low range in the
undeveloped area, low density residential and commercial. Similar pollutants
concentration can be found high range in the high density resident and commercial
as well as large industrial area. The use of constructed wetlands, usually with
accompanying ponds, is now a routine best management practice (BMP) for
controlling the quality of runoff (Kadlec and Wallace, 2009). In agricultural runoff
treatment, concentration of main contaminants like suspended solids, nitrate,
phosphorus and chemicals depend upon farming practices, rainfall intensity soil type
and topography. CWs are only the economically feasible means of controlling
phosphorus, nitrogen and ability to abate the pulse of some pesticides.
Nevertheless, this lesson deals mainly with the conventional use of constructed
wetlands, which are to treat the pre-treated municipal wastewater, or so-called
primary effluent. The typical treatment cycle is shown in Figure 3.1.
Fig 3.1: Constructed Wetlands in the treatment cycle
Constructed
Wetlands
Secondary
Treatment
Primary
Treatment
Disinfection
or
Tertiary
Treatment
Raw
Wastewater
Primar
y
Effluent
Second
ary
Effluent
Final
Discharge
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3.1.2 Horizontal Subsurface Flow Constructed Wetlands
In a horizontal subsurface flow CWs, water flows from inlet to outlet in the horizontal
path through a bed of a relatively homogenous medium, like gravel, sand or stones of
different sizes.
HSF wetlands are typically comprised of inlet piping, clay or synthetic liner, filter
media, emergent vegetation, berms, and outlet piping with water level control. The
main objective of impermeable layer made of plastic or soil with very low
permeability, to prevent seepage of wastewater mixing into the groundwater. During
the passage through the wetland, wastewater will come into contact with a network of
aerobic, anoxic and anaerobic zone (Vymazal, 1998). The decomposable parts of the
wastewater are transformed by microorganisms which are attached as bio-film in
plant roots and the filter medium. The vegetation in the wetland consists of emergent
macrophytes (rooted aquatic plants with leaves above the water surface).
Fig 3.2: Cross section of an HSF constructed wetland. (Picture from Ingenieurbüro Blumberg)
It is recommended to let clean water enter over CWs surface during the planting
phase. Plant growth may be inhibited by the high oxygen demand in wastewater
coming from a septic tank effluent. The wastewater can be introduced after a few
weeks of plant growth. The role of macrophytes is discussed in detail in chapter 6 of
this thesis report. Similarly, removable of organic matter, TSS, nitrogen and
phosphorus reduction are described in section 3.6 of this chapter.
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Wastewater needs to be pre-treated in a septic tank or similar, to remove solids,
before entering at HSF wetland. If without pretreatment allowed to enter into the
wetland, these could effectively clog the medium and prevent water passage and
subsequent treatment.
Kickuth developed a concept of wastewater treatment through constructed wetlands
with horizontal flow and known as „‟ Root Zone Method‟‟ system. This method was
put in operation in Germany in 1974. Soil was used as a medium as a result low
hydraulic conductivity and suffered from surface runoff. But the problem was
overcome by the use of more porous media e.g. gravel (Vymazal, 1998). In Europe,
the most common term for HSF constructed wetlands is the Reed Bed Treatment
System‟‟ (RBTS) because of frequently used plant is Common Reed (Phragmites
australis). Detail design criteria and recommendation of HSF constructed wetlands
are described in chapter 4.
3.1.3 Vertical Subsurface Flow (VSF) Constructed Wetlands
In VF CWs, wastewater is distributed over the whole surface area of beds and
allowed to flow vertically through bed material. The earliest VSF Constructed
Wetlands in Europe were so-called „‟ infiltration fields‟‟ in the Netherlands and this
system is also known as Seidel-System or Max Planck Institute Process (Brix, 1994).
Fig 3.3: Detail cross- section of Vertical Flow Subsurface CWS
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The water is fed under the intermittent loading system and then the water percolates
down through the sand medium. This enables diffusion of oxygen from the air into the
bed. As a result, VF CWs are far more aerobic than HF CWs and provide suitable
conditions for nitrification. VF CWs do not provide any denitrification and are also
very effective in removing organics and suspended solids. Removal of phosphorus is
low unless media with high sorption capacity are used. As compared to HF CWs,
vertical flow systems require less land. The system is typically comprised of a
preliminary settling/distribution ditch, alternative infiltration compartments with
soil/sand media, a discharge via drain and an effluent ditch as shown in fig 3.3. The
bed is planted with emergent wetlands plants (typically Phragmites). Detail design
criteria and recommendation of VSF constructed wetlands are described in chapter 4.
3.1.4 General advantage and disadvantage
Constructed wetlands are widely acceptance and many advantages compared
to conventional treatment systems, and some of them are presented here.
CWs are simple in construction, low operation and maintenance costs with or
without low energy demand. They have high ability to tolerate fluctuations in
flow, high process stability, so they can stand low loading for an extended
period of time, e.g. during a vacation, and also handle extra large loads during
a short period, and still keep a good effluent quality . Untreated water is not
exposed to the atmosphere during the treatment process, hence there are less
odor problems and the risk associated with human or wildlife exposure to
pathogenic organism is minimized and fewer problems with mosquitoes
(Kadlec and Wallace,2009). They are used to enhance aesthetic of open
spaces, help for recreational and educational opportunities. Reed harvesting
as a regenerative energy source may contribute to generate electricity
(biogas). The treated effluent water might be acceptable as irrigation water for
cash crops, lawns, public parks and golf course.
They generally require larger land areas than conventional wastewater systems. But
compared to FWS constructed wetlands, SSF constructed wetlands require less land
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area. They can tolerate temporary water level draw downs, but not complete drying
(a base flow of water is required).The Evapotranspiration rate of aquatic macrophytes
in treatment wetlands is high thus reducing the water volume available for irrigation.
Some disadvantages with HSF wetlands are risk of shortcuts on the surface between
inflow and outflow and possibility of clogging if pre-treatment is insufficient. In
temperate regions the performance might be decreased during winter. Constructed
wetlands are regarded as an attractive alternative for small to medium-sized
communities in sparsely populated areas and in developing countries (Brix, 1993).
3.2 Characteristics of Wastewater.
In order to design wastewater treatment systems, it is very necessary to understand
the nature of wastewater. The treatment capacity and treatment efficiency of systems
are calculated based upon the wastewater characteristics because the effluent
quality depends upon the influent characteristics. Wastewater generally includes a
large variety of contaminants and can be very complex in composition, originating
from households, industries and storm water collection. In this project no industrial
wastewater will be considered, only domestic and stormwater.
Fig 3.4: A range of possible source of household wastewater showing wastewater from toilet, kitchen, bathroom, laundry and others. (Source: http://www.unep.or.jp/ietc/publications/freshwater/sb_summary/2.asp)
Typical components of wastewater are microorganisms, biodegradable and other
organic material, nutrients, metals and other inorganic material coming from
household and paved surface area. Domestic wastewater can be categorized into
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two groups like black water and grey water. Black water is especially generated from
the WC, containing faeces and urine. Grey water is wastewater coming from the
kitchen, bathroom and laundry (Ujang and Henze 2006). The water treated in the
constructed wetland is especially domestic and surface run-off from pavement. This
literature study focuses on the parameters that were tested in the project. Chemical,
physical and biological characteristics are described below.
3.2.1 Chemical Characteristics
Organic material Wastewater contains a vast number of organic materials that are comprise of
carbohydrates, fat, proteins, higher fatty acids and soluble organic acids, originate
from kitchens and bathrooms, and toilets. It is hard to determine all organic materials
in detail but they share common characteristics that can be tested in more collective
analyses. The parameters included in the analyses of this study, except for organic
nitrogen, are listed below.
Table 3.2: Analysis of domestic waste water by the American Public Health Association (Source: Wastewater Technology, by W.Fresenius and W. Schneider, 1989)
Biochemical oxygen demand, (BOD5) BOD indicates the amount of biodegradable substances in wastewater, and is widely
used and recognized as an important parameter in wastewater treatment processes.
It is a measure of the oxygen consumption of microorganisms, when oxidizing
organic matter in wastewater, at 20°C. For the measurement of BOD5, the test is
normally runs for five days, and the result is then more properly designated as BOD5.
It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen
consumed per liter of solution. If the concentration of BOD5 is near to 300 mg/l, 200
Substances mg/l
Pollution
High Average Low
Total solids 1000 500 200
Suspended solids 600 350 120
Total dissolved solids 500 200 100
Total nitrogen 85 50 25
Chloride8as CaCO3) 175 100 15
Alkalinity 200 100 50
Fats 40 20 0
BOD5 300 200 100
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mg/l , then it is called high and average level of polluted wastewater as per the
American Public Health Association as shown in table 3.2.
Chemical oxygen demand (COD) COD describes the amount of chemical oxidant, usually potassium dichromate,
required to oxidize the organic matter. It is expressed in milligrams per liter (mg/L),
which indicates the mass of oxygen consumed per liter of solution.
Table 3.3: Per capita contributions of domestic wastewater characteristics
PH The pH is a useful and important parameter in measuring the conditions of
wastewater during the whole treatment process. The pH is a logarithmic index of the
concentration of hydrogen ions (H+) in water solution. A pH value of 7 indicates
neutral conditions. Above 7 is basic and below is acid. Especially metabolic reactions
in biological processes are highly pH dependant and sensitive to low pH levels or
changes in pH.
3.2.2 Physical Characteristics
These characteristics are concerned with detection of wastewater by using the
physical senses like temperature, odor, color, and feel of solid material.
Suspended solids and total solids Suspended solids represent that fraction of total solids in any wastewater that can be
settled gravitationally. Suspended solids can further be classified into two fractions
like organic which is volatile and inorganic which is fixed. However, organic matter is
Item Range of values in wastes (g/capita-day)
BOD , 5 days,20 °C 45 - 54
COD 1.5 to 1.9 x BOD5
Total solids 170 - 220
Suspended solids 70 -145
Grit (inorganic, 0.2 mm and above)
5 -15
Alkalinity (as CaCO3) 20 - 30
Chlorides 4 - 8
Total nitrogen, as N 6 -12
Total phosphorous, as P 0.6 – 4.5
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present in the form of either setteable form or non-setteable (dissolved or colloidal)
form. If the organic fraction of suspended solids present in sewage is discharged
untreated into streams, it leads to sludge deposits and subsequently to anaerobic
conditions. These are also the main cause of clogging effects in the constructed
wetlands. The wastewater are characterized as high, average and low level polluted
as per the concentration of suspended solid, dissolved solids and total solids if they
meet the above mentioned requirement in table 3.2.
Temperature Temperature affects chemical and biological processes in a profound way. The rate
of chemical reactions and biological activity increases with increased temperature.
Similarly, metabolism and growth of microorganisms are affected by this but only up
to a certain level, after which the rate becomes lower and eventually lethal
temperatures stop the growth altogether. Different microorganisms tolerate different
temperature intervals.
Turbidity Turbidity in water is caused by suspended matter, e.g. clay or silt, small organic and
inorganic particles, plankton and protozoa. Therefore, turbidity is sometimes used as
surrogate for gravimetric measurement of suspended matter. The particle size of the
present substances ranges between 1 to 300 μm. The turbidity can be measured by
a decrease in the intensity of the radiation passed through the liquid or by the
intensity of the stray light. Turbidity is often measured using a turbidimeter, consists
of nephelometer, light source and photometer (Kadlec and Wallace, 2009). The unit
for turbidity measured with this instrument is nephelometric turbidity units (NTU).
3.2.3 Biological Characteristics
Microorganisms A microorganism is unicellular or lives in a colony of cellular organisms that is too
small to be seen by the human eye. The study of microorganisms is called
microbiology, a subject that began with Anton van Leeuwenhoek's discovery of
microorganisms in 1675, using a microscope microscope1.
1 Information share from http://en.wikipedia.org/wiki/Microorganism
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Microorganisms are very diverse and classified into two major groups like
prokaryotes and eukaryotes. The prokaryotes are divided into two groups like
bacteria and archaea. The eukaryotes can be divided into three groups, fungi, algae
and protozoa. Microorganisms are the cause of many infectious diseases. The
organisms involved include pathogenic bacteria, causing diseases such as plague,
tuberculosis and anthrax; protozoa, causing diseases such as malaria, sleeping
sickness and toxoplasmosis; and also fungi causing diseases such as ringworm,
aspergilosis. Bacteria are unicellular and can have a number of different shapes and
sizes (0.1-40 μm). They are universally present in human feces, with normal
population of about 1011 organisms per gram (Kadlec and Wallace, 2009).
3.3 Nutrients
Nitrogen, phosphorus and potassium -- there are valuable nutrients contained in
wastewater. Excessive amounts of nutrients, especially nitrogen and phosphorus,
speed up the eutrophication process. Eutrophication is the slow, natural nutrient
enrichment of streams and lakes and is responsible for the "aging" of ponds, lakes,
and reservoirs. As algae grow and then decompose, they deplete the dissolved
oxygen in the water. Excess nutrients in water usually results toxicity to aquatic life
like fish, offensive odors, unsightliness, and reduced attractiveness of the water for
recreation and other public uses. Similarly excessive nitrate (NO3-) in drinking water
can cause human and animal health problems, particularly for small babies.
3.3.1 Nitrogen
Nitrogen occurs in different forms in municipal or domestic wastewater are ammonia
(NH4+),nitrite (NO2
-), nitrate (NO3-), nitrous oxide (N2O) and nitrogen gas (N2). In the
atmosphere, concentration of nitrogen is up to 78 %. Similarly, organic nitrogen is
also present in wastewater in the form of amino acid, urea and uric acids. Amino
acids are the main component of proteins, which is essential to all form of life. Urea
(CNH4O) and uric acid (C4N4H403) are the simplest form of organic matter in aquatic
system. Nitrogen in domestic sewage comprises about 60% ammonia and 40%
organic nitrogen (Wallace and Kadlec, 2009). The wastewater can be defined as
high, average and low level of pollution, if total nitrogen concentration exceeds up to
85, 50 and 25 mg/l respectively (see table3.2). Nitrogen removal process is described
in detail in section 3.6 of this chapter.
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3.3.2 Phosphorus
Phosphorus is an important constituent of all life. This nutrient occurs naturally in
most plants and animals and readily enters the food supply of humans from these
sources. It is one of the 20 most abundant elements in the solar system, and the 11th
most abundant in the earth‟s crust (MPCA, 2007). Human activities, however, have
resulted in excessive loading of phosphorus into many freshwater systems.
Excessive amounts of phosphorus may lead to the increased growth of algae and
other microorganisms, causing water quality to degrade. Water containing large
amounts of algae can become unsafe to drink and can cause vomiting and diarrhea.
Contact with algal blooms can cause skin irritation, thus impacting on the recreational
use of water.
In domestic wastewater, phosphorus exists in the form of orthophosphate,
dehydrated orthophosphate and organic phosphorus. Most phosphorus is conversed
into orthophosphate forms (H2PO4-, HPO4
2-, and PO43-) under the biological oxidation
(Cooper and Job, 1996). In wetlands, lakes, ponds and rivers particulate phosphate
may be deposited by sedimentation, trapped by macrophytes stems or sorbed to
biofilms.
3.4 Treatment requirements
3.4.1 Legislation
In Germany, a framework act of the Federation, the Federal Water Act
(Wasserhaushaltsgesetz) provides fundamental requirements for water management
measures. According to Article 7a of the Act, a permit for the discharge of wastewater
shall be granted only if the pollutant load of the wastewater in question is kept as low
as is possible through application of appropriate procedures using the best available
technology. The Federal Government shall establish relevant requirements, by
means of ordinances approved by the Bundesrat that are in keeping with the best
available technology2.
2 Promulgation of the New Version of the Waste Water Ordinance of 17. June 2004,this ordinance will come
into force on 1 January 2005 http://www.bmu.de/english/water_management/doc/3462.php
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European Communities (EC) developed a Waste Water Treatment Regulations 2005.
These Regulations contain general binding rules requiring sanitary authorities to
ensure that waste water treatment plants do not cause a nuisance through odours or
noise emissions. The Regulations set a legal requirement for waste water treatment
plants to be designed, constructed, operated and maintained so as to avoid causing
nuisance from odor emissions or noise. Operators of such plants, including sanitary
authorities, must indicate to the Environmental Protection Agency each year all steps
taken to comply with the Regulations and, on request from the Agency, must furnish
copies of all complaint records.
The Urban Waste Water Treatment Directive of EC has already contributed to an
improvement of the quality of big European rivers by reducing BOD levels by 20-
30%, of phosphorus concentrations by 30-40% and of NH4-N levels by around 40%.
Austria, Denmark and Germany, plus with certain restrictions the Netherlands have
shown that successful and timely implementation is possible, leading to significant
improvements in water quality by achieving compliance rate of about 2/3 of the
pollution load covered by the 1998 and 2000 deadlines (H. Blöch ,2005). The
Austrian Water Act (1959/1990) is based on the principle of provision with respect to
water considering whole environment and its relationship with water and wastewater
are taken into consideration. The effluent values from treatment plant should be
within limiting values, which is legally regulated (Vymazal, Brix, 1998).
Table 3.4: Effluent standards of different European countries for small scale discharges into the surface water (modified data of Diederik P. L. Rousseaua, Peter A. Vanrolleghemb, and Niels De Pauwa)
Country Remarks COD BOD SS TN NH4-N TP Reference
Belgium 250 60 50 - - - VLAREM II (1995)
Germany 1000 – 5000 PE
110 25 - - - - Joachim (2000)
Austria 500 – 5000 PE
75 20 - - 5 2 AES ,1996
Poland < 2000 m
3
day-1
150 30 50 30 6 5 Kempa (2001)
Czech 500 – 2000 PE
120 30 35 - - - Czech Law No. 61/2003
Italian 125 25 35 35 15 10 Italian Law (1999)
Netherlands 750 150
250 30
70 30
- -
- -
- -
Debets (2000)
Sweden 10 15 0.3 – 0.5
Linde and Alsbro (2000)
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Wastewater coming from domestic use, industry, agriculture or any other activity that
can contaminate the water of lakes, rivers and aquifers, should be treated before
discharge. To protect the environmental and water course, effluent from wastewater
treatment systems should be standard limit governed by national law. Some of the
European country has set the standard norms of effluent wastewater as shown in
table 3.4.
3.4.2 Guidelines
A over growing population, unrelenting urbanization, increasing scarcity of good
quality water resources and rising fertilizer prices are the driving forces behind the
accelerating upward trend in the use of wastewater, excreta and greywater for
agriculture and aquaculture. The health risks associated with this practice have been
long recognized, but regulatory measures were, until recently, based on rigid
guideline values whose application often was incompatible with the socio-economic
settings where most wastewater use takes place.
In 2006, WHO published a third edition of its guidelines for the safe use of
wastewater, excreta and grey water in Agriculture and Aqua culture. These
guidelines are divided into four volumes, which propose a flexible approach of risk
assessment and risk management linked to health-based targets that can be
established at a level that is realistic under local conditions. Some of the
recommendations regarding reuse of treated wastewater for irrigation purposes and
decentralized wastewater treatment systems will be presented here. To reuse water
for activities and areas with public access, for example parks and irrigation of crops
that will be eaten raw or that are not commercially processed, WHO (2004)
recommends that there should be no detectable faecal coliforms /100 ml of water,
and BOD values of less than 10 mg O2/l. This is called unrestricted irrigation. For
restricted irrigation, when irrigating areas with limited or no public access and cereal
crops, industrial crops, fodder crops, pasture and trees, the recommendations from
USEPA (2004) are faecal coliform concentrations of less than 200 faecal coliforms
/100 ml and BOD and SS levels of less than 30 mg/l. In the guidelines from WHO
(1989) on safe wastewater reuse, the recommended limit was 1000 faecal coliforms
/ml for unrestricted irrigation. in the new guidelines from 2006, WHO validated their
earlier general recommendation of 1000 E.coli/100 ml for unrestricted wastewater
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use in agriculture, but other values were also given, e.g. 105 E.coli/100 ml for drop
irrigation of higher crops (WHO, 2006).
3.5 Hydraulics in Constructed Wetlands
3.5.1 Retention Time (RT) and Hydraulic Loading Rate (HLR)
Nominal retention time is defined as the wetland water volume involved in flow
divided by the volumetric water flow. Alternatively, it can be described a measure of
retention time, it takes for the whole water volume of a wetland to be replaced. It is
defined as RT = V/Q, where V is the total water volume and Q is the flow through the
wetland. The assumptions are steady-state conditions, i.e. the inflow is equal to the
outflow (Q = Q in = Q out), and no mixing of the water column. The total volume of the
wetland is occupied by the medium, e.g. sand, gravel. These medium having the
porosity holds water. The actual retention time for a constructed wetland is given by
the following expression (Kadlec and Wallace, 2009):
…… (1)
…... (2)
A = surface area of the wetland (m2), h = depth of water-filled part of the wetland (m)
= porosity, % expressed as decimal, Q = average flow through the bed (m3/d)
= detention time (d), q = hydraulic loading rate (m/d)
Above expression in eqn. 1, takes into consideration the porosity of the medium but
not plant roots, biofilms or non degradable residues. Over longer time, the
accumulation of non-degradable residues in the pore spaces and the spreading of
plant roots will also add resistance to the flow. Eventually this could lead to clogging
of the medium and unwanted surfacing of the wastewater. The void fraction, also
termed media porosity, ranges usually from 0.3 - 0.45 depending on the soil material
chosen, e.g. sand, gravel or clayey soils (Vymazal, 1998a). In surface flow systems,
the “reactive” volume is defined as the volume of the free water body above the
substrate minus the portion occupied by the submerged plant parts, e.g. stems,
leaves, detritus, but also settled solids. The porosity of surface flow wetlands has
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proved difficult to exactly measure, thus, porosity values for surface flow wetlands in
the literature are highly variable. For example, Reed (1995) recommended wetland
porosity values ranging from 0.65 - 0.75 for fully vegetated surface flow beds.
To meet advanced treatment standards in surface flow as well as in subsurface flow
wetlands, the HRT should be at least 5 days (Vymazal, 1998a; WPCF, 1990). Reed
(1995) suggested a hydraulic retention time of at least 6 to 8 days to ensure
adequate nitrification rates. It can be concluded that there are no universally
applicable recommendations in the literature.
Hydraulic loading rate also play important role in the treatment efficiency of CWs.
There is also relationship between nominal detention time and hydraulic loading rate
as expressed in eqn. 2. From the expression, it can be seen that hydraulic loading
rate is inversely proportional to nominal detention time for the given wetlands depth
(Kadlec and Wallace, 2009). Hydraulic loading rate therefore embodies the notion of
contact duration, just as nominal detention time does.
Horizontal subsurface flow wetlands
2.0 - 5.0 cm/d for secondary treatment (Vymazal, 1998)
< 20 cm/d for tertiary treatment (Vymazal, 1998)
Vertical flow wetlands
6.0 cm/d (Mennerich, 2003)
The required energy to overcome the resistance of the medium, plant roots and
residues, is provided by the difference in hydraulic head between the inlet and the
outlet of the wetland. The time it takes for the water to pass from the inlet to the outlet
of the wetland may be less than the nominal retention time since the velocity of the
water may be higher in certain channels of the bed and shortcuts can be formed.
According to USEPA (2000) the actual retention time has frequently been reported to
be 40-80 % less than the theoretical retention time. This is one of the reasons to loss
of pore volume, preferential flow and dead volume, i.e. stagnation pockets sometimes
exits.
3.5.2 Porosity and Permeability
Porosity can be defined as the ratio of fraction volume of voids over the total volume
of materials. Soil porosity refers that pore spaces are filled with air, other gases, or
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water. Large pores known as macropores allow the ready movement of air and the
drainage of water. They are also large enough to accommodate plant roots and the
wide range of tiny animals that inhabit the soil (Brady and Weil, 1999; Munshower,
1994). Clay soils have numerous micropores which help to hold large quantities of
water, but since they have few macropores cause very slow infiltration rates. The
pores in the clays may be so small and hold water so tenaciously that the water is not
available to plants. Sandy soils with numerous macropores but few micropores have
higher infiltration and percolation rates but a lower water-holding capacity than other
soil textures. (Munshower, 1994).
Permeability is the measure of a soil‟s ability to transmit water and it is largest for
coarse gravel with same size grains. In a less sorted sample, the small grains fill the
voids between the large grains and lower the permeability. The permeability can be
expressed with a coefficient, called hydraulic conductivity.
Fig 3.5: Permeability test model with different material (Gravel, Sand, Silt and clay) (Source: http://techalive.mtu.edu/meec/module06/Permeability.htm)
3.5.3 Soil clogging
Clogging is a well known phenomenon in soil filter as well as Constructed wetlands
and occurs in the wetlands bed by different mechanism like sediment deposition,
chemical precipitation and Biomat formation. Clogging caused soil pore spaces
decrease which restricts the flow of water through the bed media. Mostly suspended
(minerals) solids deposited within the inlet region of HSF wetland beds due to the low
flow velocity and such kind of deposition occurs within the 5% of the wetland bed
(Kadlec and Wallace, 2009). Biological clogging occurs when bacterial growth or its
by-products reduce the pore diameter. Biological clogging frequently associated with
organic and inorganic solids, which are entrapped by biofilms for the formation of
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Biomet. Kadlec and Watson (1993) found approximately 10% voids blocked by
volatile and inorganic solids. Especially, the combined effects of short-term and long
term bed clogging are reducing the hydraulic conductivity of the inlet zone of the HSF
bed and upper 0-15 cm of bed in VSF CWs. Purification efficiency drops significantly
when constant ponding occurs. Clogging is dependent on the height of organic mass
loading.
Therefore the system has to be designed large enough so that resting periods in
parts of the filter bed can occur. Another possibility to avoid clogging is to keep the
load so low that it does not occur due to the natural degradation processes. The
experiences with soil clogging in constructed wetlands differ widely, since the
problem depends on many factors (Platzer and Mauch, 1997). Sufficient soil (or bed)
aeration is the main factor for the proper functioning of VFBs and wastewater needs
to be pumped onto the VFBs intermittently (4-12 times per day). Communal
constructed wetlands with VF CWs should have at least 4 beds in order to feed them
intermittently loading on a regular basis like some beds 6 weeks in operation and 2
weeks of rest for better oxygenation.
The hydraulic loading should not exceed 150 L/(m²·d) for domestic wastewater under
normal conditions (during rain events, a hydraulic loading up to 500 L/(m²·d) can be
acceptable). The TSS loading should be less than 5 g/(m²·d) and this requires
efficient pre-treatment and organic loading (COD) should not exceed 20 g/ m²·d
(Winter and Goetz, 2003). Adequate plants with developed rhizome/root system play
an important role in maintaining and restoring soil conductivity and withstand against
the clogging.
3.6 Treatment mechanisms in Constructed Wetlands
Constructed Wetlands are effective in treating many contaminants, including organics
(BOD, COD), suspended solids, nitrogen and phosphorus as well as, and also in
reducing metals, organics and pathogens from wastewater (Vymazal, 1998). In a
subsurface flow wetland TSS and BOD are generally removed effectively while the
removal of nutrients (P and N) are variable and depends on loading rate, type of
substrate, oxygen supply and composition of wastewater (Brix 1993). The major
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processes for removal of pollutant are complex within the wetland system as
described as below.
3.6.1 Organic compounds removal (BOD and COD)
The organic strength of wastewater can be measured as BOD (Biochemical Oxygen
Demand) and COD (Chemical Oxygen Demand). However, BOD is the more
important and frequently used parameter for domestic or municipal wastewaters
(Kadlec and Knight, 1996). Settable organics are rapidly removed in wetland system
under quiescent condition by deposition and filtration. Organic compounds are
degraded aerobically as well as anaerobically. Firstly, organic compounds are
biologically decomposed by the heterotrophic microorganisms under aerobic
condition and converted to water and carbon dioxide (Vymazal, 1998). Similarly,
anaerobic degradation is a multi-step process that occurs within constructed
wetlands in the absence of dissolved oxygen (Cooper et al. 1996). Anaerobic
degradation is much slower than aerobic degradation. The oxygen needed to support
the aerobic process is supplied directly from the atmosphere via diffusion or oxygen
leakage from macrophytes roots in the rhizosphere (Cooper, 1996)
The removal rate of organic matter is temperature-dependent since higher
temperatures have a positive effect on microbial activity. The growth rate,
reproduction, metabolism and the mobility of organisms, e.g. rates of biochemical
reactions, usually double when temperature is increased by 10°C within the given
tolerance range of an organism. The decomposition of BOD in all types of
constructed wetland systems is usually very efficient and has been reported to be on
the range of 70 - 95 % (Reed, 1995) for pre-treated municipal or domestic
wastewaters. However, the BOD removal rate is poorer at low input concentrations
due to the internal background production of about 1 - 6 mg/L BOD. COD removal
performance is usually slightly lower than of BOD since some groups of organic
compounds cannot be biologically decomposed by microorganisms. This results in
background levels ranging from 30 to 100 mg/L COD (Kadlec and Knight, 1996).
3.6.2 Removal of Suspended Solid (SS)
Suspended solids are setteable and floatable particles in wastewater consisting of
organic and inorganic matter. The major removable process of setteable suspended
solids is sedimentation and filtration. Non-settling or colloidal solids are removed at
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least partially, by bacterial growth (which results in the settling of some colloidal
solids and the microbial decay of others) and collusions with the adsorption to other
solids (plants, pond bottom, suspended solids) (stowell et al. 1981).
Kadlec and Wallace (2009) found the median values of inlet and out let TSS
concentration in 31 vertical flow wetlands were 90 mg/l and 12 mg/l respectively, with
the removable efficiency of 87%. Similarly, by the experiments showed that
suspended solids are efficiently removed in both types of constructed wetlands and
TSS effluent concentrations are generally less than 20 mg/L and often less than 10
mg/L in both types of constructed wetlands (Brix, 1994). According to Reed (1995)
and Kadlec and Knight (1996), TSS background concentrations of about 2 - 5 mg/L
TSS can be expected.
The influent should be at least primary pre-treated to avoid the high TSS
concentrations typically found in raw wastewaters. Suspended solid of wastewater
are filtered and settled within the first few meters beyond the inlet zone. These could
lead a major threat for good performance of subsurface flow systems (Vymazal,
1998).
3.6.3 Nitrogen Removal
Nitrogen (N) in municipal wastewater is usually present as organic compounds, e.g.
urea and amino acids, and as inorganic form, almost exclusively ammonium (NH4+).
The removal mechanisms for nitrogen in constructed wetlands are manifold and
include ammonification, nitrification-denitrification, plant uptake and matrix adsorption
(Vymazal et al. 1998).
3.6.3.1 Ammonification
Ammonification is the process where the bacterial conversion of organic N into
inorganic N, especially NH4+-N in untreated wastewaters, which is also known as
mineralization. Ammonification rates are fastest in the oxygenated zone and
decrease in the facultative anaerobic zone. Reedy and Patrick et al. (1984) described
about the Ammonification process which are highly dependent on temperature, pH
value ,C/N ratio of the residue, available nutrients in the system and soil condition
(texture and structure) From the literature data, that the rate ammonification
increased by double with a temperature increase of 10°C.
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Fig 3.6: Nitrogen transformation in constructed wetlands (Cooper et al., 1996)
3.6.3.2 Nitrification
Nitrification is the biological transformation of ammonium to nitrate with nitrite as an
intermediate in the reaction sequence. Nitrification is a chemoautotrophic process
and energy for growth of nitrifying bacterial is derived by the oxidation of ammonia
and carbon dioxide is used as a carbon source for synthesis of new cells (Cooper
and Job, 1996). Nitrification includes two consecutive processes where ammonium-N
is oxidized by autotrophic bacteria to nitrite (NO2-), after it is formed, immediately is
oxidized to nitrate (NO3 -). Nitrite occurs therefore in very low concentrations while
nitrate may occur in high concentrations.
The first step: ammoniacal nitrogen is converted to nitrite in the presence of Nitrosomonas bacteria:
1) NH4+ + 1.5O2 NO2
- + 2H+ + H2O
The second step: Nitrite is converted to nitrate in the presence of Nitrobacter bacteria:
2) NO2 - + 0.5O2 NO3
-
Ammonification
Organic N
NH4+
NO2-
NO3-
N2,N2O
Biomass
uptake
Biomass
uptake
Anaerobic zone Aerobic zone
Volatilisation Matrix
adsorption Biomass
uptake
N2,N2O
gas
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Equations 1) and 2) can be comprised as follows that describes the entire nitrification process:
3) NH4
+ + 2 O2 NO3 - + 2 H+ + H2O
According to Vymazal (1998), nitrification is influenced by temperature, pH value,
concentration of ammonium-N and dissolved oxygen. Especially, temperature and pH
have a major effect on the rate of nitrification. The optimum temperature for
nitrification ranges from 25 °C to 35 °C in water and from 30 °C to 40 °C in soils.
Temperatures below 15 °C affect the nitrification rate more significant compared to
temperatures between 15 °C and 35 °C. Minimum temperatures for growth of
Nitrosomonas and Nitrobacter are 5 °C and 4 °C, respectively (Cooper, 1996).
Nitrifying bacteria are sensitive organism and susceptible to a wide range of
inhibitors. Nitrification can exists on the optimum pH ranges from 7.5 to 8.6, however,
can also occur at much lower pH values (Vymazal, 1998).
3.6.3.3 Denitrification
The biological reduction of nitrate (NO3-) to nitrogen gas (N2) by facultative
heterotrophic bacteria is called Denitrification. “Heterotrophic” bacteria need a carbon
source as food to live. There are several genera of heterotopic bacteria including,
Achromobacter, Aerobacter, Alcaligenes, Bacillus, Brevibacterium, Flavobacterium,
Lactobacillus, Micrococcus, Proteus, Pseudomonas and Spirillum are capable of
dissimilatory nitrate reduction (Cooper, 1996).
Denitrification occurs when oxygen levels are depleted and nitrate becomes the
primary oxygen source for microorganisms. The process is performed under anoxic
conditions, when the dissolved oxygen concentration is less than 0.5 mg/L, ideally
less than 0.2. When denitrifying bacteria break apart nitrate (NO3-) to gain the oxygen
(O2), the nitrate is reduced to nitrous oxide (N2O), and, in turn, nitrogen gas (N2). In
unbalanced equation form:
NO3-
→ NO2 - →NO → N2O → N2
Since nitrogen gas has low water solubility, it escapes into the atmosphere as gas
bubbles. Free nitrogen is the major component of air, thus its release does not cause
any environmental concern. Since denitrifying bacteria are facultative organisms,
they can use either dissolved oxygen or nitrate as an oxygen source for metabolism
and oxidation of organic matter. If dissolved oxygen and nitrate are present, bacteria
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will use the dissolved oxygen first. That is, the bacteria will not lower the nitrate
concentration. Denitrification occurs only under anaerobic or anoxic conditions.
Conditions that affect the efficiency of denitrification include nitrate concentration,
anoxic conditions, and presence of organic matter, pH, temperature, alkalinity and
the effects of trace metals.
Cooper et al. (1996) pointed out that optimum pH values for denitrification are
between 7.0 and 8; however, pH value rised due to the alkalinity production during
denitrification. Denitrification is also strongly temperature dependent and proceeds at
very slow rates, at temperature below 5°C.
3.6.3.4 Plant uptake
Nitrogen removable mechanism also depends upon plant uptake system especially
macrophytes which are used in CWs will take up nitrogen in its mineralized state and
incorporate it into its biomass and tissue through their root system. However, the
potential nitrogen uptake capacity by plants is limited by its productivity (growth rate)
and the nutrient content in the plant tissue.
The uptake capacity of emergent macrophytes, when the biomass is harvested, is
roughly on the range of 1000-2500 kg N ha-1yr-1 and highly productive Water
Hyacinth (Eichhornia crassipes) have higher uptake capacity up to nearly 6000kg N
ha-1yr-1 whereas submerged macrophytes is lower range of about 700 kg N ha-1yr-1
(Brix,1994a, Vymazal,1998). Similarly, Gersberg et.al (1985) pointed out that the
amount of nitrogen removed with biomass under optimum condition can be achieved
10-16% of the total removed nitrogen. Furthermore, nitrogen is only temporarily
stored in the emergent plant biomass and will return back to the wetland system by
decomposition process through an annual cycle of growth and die back. Regularly
harvesting of the aboveground biomass can be realized in order to improve the total
nitrogen removal efficiency. Although wetland plants show generally a high
productivity and can incorporate considerable amounts of nitrogen into their biomass,
the uptake rates are relatively insignificant compared to the total nitrogen loading
charged into the constructed wetland (Brix, 1994a).
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3.6.3.5 Sediment adsorption
Removal of nitrogen through matrix adsorption (fixation of nitrogen at soil particles)
accounts for the third pathway nitrogen can be removed from wastewater. In a
reduced state of ammonium N is stable and can be adsorbed onto active sites of the
bed matrix. However, cation exchange in the bed matrix is not a long-term sink for
NH4-N removal and NH4-N sorption in continuous flow will be equilibrium with NH4-N
sorption solution. Only in the intermittent loading of a system will show rapid
removals of NH4-N by adsorption mechanism due to depletion of NH4-N during rest
periods (Cooper, 1996). This process amounts to about another 10 % of the total
nitrogen removal rate and can be considered as insignificant (Wissing, 2002).
3.6.4 Phosphorus Removal
Phosphorus in wastewater occurs mostly in the form of phosphates and organic
phosphorus. The main mechanisms for phosphorus removal in subsurface flow
systems are chemical and physical adsorption, precipitation in the soil matrix and
plant uptake. The adsorption and retention of phosphorus in wetland soils depends
primarily on the soil type and chemical composition, and further, surrounding
conditions such as pH value, redox potential (Vymazal et al.1998). In acid soils,
inorganic P is adsorbed on hydrous oxides of Fe and Al and may precipitate as
insoluble Fe phosphates and Al phosphates. Precipitation as Ca-P is the dominant
transformation at pH greater than 7.0 (Cooper, 1996).
Soil with high amounts of clay has a large capacity to bind P than non-cohesive,
coarser-textured soils (gravel beds), but the permeability is low. Hence there have
been hydraulic problems in constructed wetlands. The P removal can be improved
using a filter medium that has a large capacity to bind P, like gravel with high
amounts of calcium or iron.
Like nitrogen, phosphorus is taken up through the root system and transports it to the
growing tissues, particularly at the beginning of the growing season (in temperate
regions during the early spring). The uptake capacity of emergent macrophytes is
lower as compared to nitrogen and phosphorus removal by plant uptake is roughly
50-100 kg P ha-1yr-1(Brix, 1994a). However, the wetland vegetation acts only as a
33 Chapter 3: Wastewater treatment through Constructed Wetlands
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
temporary storage, thus, phosphorus removal through plants is limited to seasonal
uptake during the vegetation period. Phosphorus contents for plants such as reeds
ranges from 0.9 to 1.35 mg/g (dry weight) for stems, 1.0 to 1.7 for leaves, and 0.9 to
1.63 for whole shoots (Davies, 1993).Phosphorus removal by plant harvesting is also
found often less than 10% of the annual load even in lightly loaded wetlands
(Herskowitz, 1986) and Hurry et al. (1990) pointer out the uptake of phosphorus by
plant in constructed wetland is only 7 %.
3.6.5 Pathogen Removal
Bacteria and viruses are important organisms from a public point of view as well as
protozoan pathogens and helminth worms are also of particular importance in tropical
and subtropical countries. Pathogens are removed in constructed wetlands by the
suitable combination of physical, chemical and biological process (Cooper, 1996).
In the physical factor, filtration and sedimentation are major processes, which may be
involved in the reduction of pathogens in wetlands. Chemical factors include
oxidation, UV radiation, exposure to biocides excreted by some plants and
absorption to organic matter. Biological removal mechanisms include antibiosis,
predation by nematodes, protists and zooplankton, attack by lytic bacteria and
viruses and natural die-off (Cooper et al. 1996). The die-off rates of all the bacteria
and coliphage were greater in the water column than the sediment. The die-off rates
of fecal coliforms in the water and sediment were 0.256 log10 day-1 and 0.151 log10
day-1, respectively (Karim, 2004).
With the literature survey of 60 constructed wetlands around the world, the removal
efficiency of total coliforms (TC) and fecal coliforms (FC) in constructed wetlands with
emergent macrophytes is high, usually 95 to >99% while removal of fecal
streptococci is lower, usually 80–95%. Whereas TC and FC in the outflow
concentrations are usually in the range of 102 to 105 CFU/ 100 ml while for fecal
streptococci (FS) the range is between 102 and 104 CFU/ 100 ml. Bacterial removal
efficiency is a function of inflow bacteria number, therefore, the outflow numbers of
bacteria are more important (Vymazal, 2005). The removal efficiency also depends
upon the hydraulic retention time.
34 Chapter 4: Criteria for the design of subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
4 Criteria for the design of subsurface flow CWs
Constructed wetlands are usually designed as a secondary treatment for removal of
suspended solids (SS) and organic matter (BOD and COD) and as a tertiary
(advanced) treatment for nutrient removal (nitrogen and phosphorus). Primary
treatment occurs normally conventionally in septic tanks having three-room digesters
or Imhoff tanks, but also in pond systems. They also remove pathogens, heavy
metals and organic contaminants.
4.1 Basic design recommendations
4.1.1 General consideration about planning /necessary conditions
The general considerations for being able to use constructed wetlands for wastewater treatment are: Retention, enhancement and interpretation of existing ecological, landscape and
cultural values, such as trees and other native vegetation and sites of archeological
significance should be considered. These are valuable assets that will be of interest
to the local community and help to create a unique sense of place. A successful
physical pre-treatment is necessary for a good performance of all constructed
wetlands. Enough space should be availability because it is a “low-rate system” with
a higher space requirement than technical systems. Construction place of CWs
should be fully receiving sunlight instead of shadow. Urbanization and population
developments have to be considered when calculating the expected wastewater flow
rate to the constructed wetland. The use of locally indigenous species in wetland
plantings ensures that plants are adapted to local environmental conditions and that
the character of the wetland is „in keeping‟ with the surrounding landscape
The substrate used should not contain loam, silt or other fine material, nor should it
consist of material with sharp edges. Uniform distribution of the wastewater in the
inlet area and surface area. A sufficient hydraulic capacity of the beds has to be
proven by application of Darcy´s law. The surface of the beds should be flat to omit
unequal distribution or surface run off so that short circuits can be avoided. Basic
design of CWs has to take into account suspended solids and organic load. CWs
beds have to be designed considering nitrification and denitrification using oxygen
consumption, soil aeration, and availability of carbon source as additional criteria.
35 Chapter 4: Criteria for the design of subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
4.1.2 Design life
The exact design life of constructed wetlands cannot be calculated but only be
expected to have at least 30-40 years. This is one of assumption based on different
literature study. The design life will be long till CWs fulfill the objective of treatment.
There are no theoretical reasons which would indicate that constructed wetlands
would stop working after a certain length of time (at least for removal of organic
matter, nitrogen and pathogens).
The design life is determined by the design life of major components involved in
constructed wetland such as influent pump, plastic pipes, plastic lining, gravel and
sand. The pumps and feeding pipes can easily be replaced if necessary. The gravel
and sand will never need replacement. The exact design life of the plastic lining is
also unknown and the condition of the plastic lining can also not be verified in an
operational constructed wetland. If a constructed wetland ever has to be abandoned,
it is easy to use the space of the former constructed wetland for other purposes, or to
just let the plants grow wild.
4.1.3 Design parameters
There are several design parameters or approaches for subsurface flow CWs which
are used at different points in the design calculations, depending on the type of
wastewater and climate:
Average flow rate of wastewater (m3/s)
Surface area per person equivalent (in m²/p.e.)
Organic loading per surface area (in g BOD or gCOD/(m² d))
Hydraulic load (in mm/d or m3/(m2·d))
Oxygen consumption and input.
Detention time (day)
Hydraulic gradient (m/m or %)
Base slope (m/m or %)
36 Chapter 4: Criteria for the design of subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
4.2 Design principles of subsurface flow CWs
The focus of this chapter is the general principles for horizontal flow (HF) and vertical
flow (VF) constructed wetlands, which are both subsurface flow type constructed
wetlands. The filter bed is based on sand and plant roots (the gravel in the bed does
not have a filtering function, but just covers the drainage pipe and avoids puddles on
the surface layer). Detailed design of a subsurface flow CWs are described below
detail as per the literature information achieved.
4.2.1 Horizontal flow (HF) CWs
In the beginning HF CWs had some problems with surface run-off and therefore often
poor treatment results, but nowadays well-designed HF CWs are widely accepted as
a robust and low maintenance treatment system. HF CWs are an interesting option
especially in locations without energy supply and low hydraulic gradient.
Kickuth has first proposed the equation, which has been widely used for the sizing of
HSF system for the domestic treatment.
Ah = Qd (ln Co – ln Ct) / KBOD where, KBOD = KT d n …... (3) KT = K 20(θ
R) (T-20) …. (4)
t = V.n / Qd = LW d n / Qd = Ah d n/ Qd …(5) HLR = 100 Qd / Ah … (6)
Where Ah = treatment area of the wetland (m2
), Ct = outlet effluent pollutant
concentration (mg/l), Co = influent pollutant concentration (mg/l), KBOD = rate constant
(m/d) , K20= rate constant at reference temperature 20o
C (day-1
), KT
= Rate constant
at temperature dependent (day-1
), n = porosity (percent, expressed as decimal
fraction), Qd = average daily flow rate through the wetland (m3
/day), t = hydraulic
residence time (day-1), T = operational temperature (
o
C), V = volume of wetland
available for water flow (m3
), W = width of the wetland (m), L = length of wetlands
beds, d = depth of the wetland (m), θR
= temperature coefficient for rate constant.
37 Chapter 4: Criteria for the design of subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Table 4.1 Shows the parameters for the design of the two types of constructed
wetlands (FSW & SSFW) based on the Reed et al. (1995) equation.
Table 4.1: Temperature coefficient for rate constant in design equations (Source: Design manual of waste stabilization pond and constructed wetlands, S. Kayombo)
Similarly, dimension of beds are derived from Darcy‟s Law. Cross section is of beds
can be calculated by the equation (Reed et al. 1998, Cooper et al. 1996) as:
Ac = Qs / Kf (dH/ds) ... (7)
W = Ac / d …. (8)
Where Ac is the cross-sectional area of wetland bed (d*W) perpendicular to the flow
direction (m2), d is the depth (m), Kf is the hydraulic conductivity of the medium
(m3/m2.day), and dH/ds is the slope of the bed (m/m).
The most important criteria and recommendations developed for HSF constructed
wetlands are summarized as follows (Cooper et al. 1996, Vymazal et al 1998, Kadlec
et al., 2009, ATV 1997):
Specific surface area for secondary treatment is about 5 m2 PE-1 and for
tertiary treatment is 1 m2 PE-1
Organic loading should be less than 150 kg BOD5 ha-1 d-1 (usually
recommended 80 kg BOD5 ha-1 d-1)
While the top surface of the filter is kept horizontal to prevent erosion, the bed
38 Chapter 4: Criteria for the design of subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
bottom slope should be 0.5 - 1%, whereas in most cases 1% is used from inlet
to outlet to allow for easy drainage.
The depth of filter beds of HSSF CWs is normally around 0.6 – 0.8 m (allow an
additional 15 cm freeboard for water accumulation).
The hydraulic loading should be 40 mm/d for secondary treatment condition
and 200 mm/d for tertiary treatment.
Detention time in wetland should be more than 5 days.
Hydraulic conductivity of media 10-3 – 3x10-3 m/s (86 -260 m/d).
Media used in Bed are especially washed gravel, crushed stones (3-6 mm)
Media porosity should be 30 – 45 %.
In most of system, plastic liner or membrane such as HDPE or LDPE has
been used with thickness 0.5 – 1.0mm.
Hydraulic gradient should maintain 2- 5 %.
Minimum area of each the reed bed of 20 m2.
4.2.2 Vertical flow (VF) CWs
VF CWs are more suitable than HF CWs, when there is a space constraint as they
have higher treatment efficiency and therefore need less space. Kadlec and Knight
(1996) developed a first-order decay, plug flow model for all pollutants, including
BOD, TSS, total phosphorous (TP), total nitrogen (TN), ammonia nitrogen (NH4-N),
oxidized nitrogen (NO3-N, NO2-N ), and faecal coliform (FC). Their model is based on
areal rate constants instead of temperature rate constant. The Kadlec and Knight
model may be less sensitive to different climatic conditions:
…. (9)
Where Q = average flow rate through the wetland (m3/day), = treatment area of
the wetland (m2), Ce = target effluent concentration (mg/l), Ci = target influent
concentration (mg/l), C* = background pollutant concentration (mg/l), k = first order
aerial rate constant (m/d).
K-values especially depend on different the parameter of the environmental and
operation circumstances. Table 4.2 gives the first order areal rate constant, which
has been deduced from measurements of practically operated plants:
39 Chapter 4: Criteria for the design of subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Parameter Areal rate constant (k)
m/yr m/d
BOD 20 - 60 0.055 – 0.16
COD 10 – 40 0.027 – 0.11
NH4-N 10 – 40 0.027 – 0.11
TN 12 – 20 0.033 – 0.055
TP 1 – 2 0.0027 – 0.033
FC 70 – 95 0.19 – 0.26
Table 4.2: Values of areal rate constant (Vymazal et al. 1998)
In VSF CWs, wastewater is intermittently pumped onto the surface and then drains
vertically down through the filter layer towards a drainage system at the bottom. The
drainage pipes are covered with gravel. The treatment process is characterized by
intermittent short-term loading intervals (4 to 6 doses per day) and long resting
periods during which the wastewater percolates through the unsaturated substrate,
and the surface dries out. The intermittent batch loading enhances the oxygen
transfer and leads to high aerobic degradation activities. VF CWs therefore always
need pumps or at least siphon pulse loading.
Some of basic design criteria and recommendations for VF CWs are summarized for
better efficiency achievement (Cooper et al. 1996, Vymazal et al 1998, Kadlec et al.,
2009, ATV et al., 1997):
The specific surface area is required 1m²/p.e. for BOD removal only and 2 m²/p.e.
for additional nitrification is needed and bed depth is used on the range of 0.5 -0.8
m. Some VF CWs was designed in Austria, with specific area 4 -5 m²/p.e and
main layer bed depth was 0.6-0.8 m.
The organic loading per surface area should be limited to 20 gCOD/(m²·d) in
colder climates and in warm climates with about 60-70 gCOD/(m²·d)
(corresponding to approximately 30-35 g BOD/(m²·d), with 90% nitrification .
Bottom slope of 0.5 - 1% in direction to the outlet.
Nowadays mostly sand and gravel are used for media with permeability of 10-3 –
10-4 m/s.
The depth of the sand filter beds should be at least 50 cm, with an additional 20
cm of gravel at the base (to cover the drainage pipes), 15 cm gravel on the top of
the bed and 15 cm freeboard for water accumulation. The gravel on top is there to
prevent free water accumulation on the surface, and could in actual fact be
40 Chapter 4: Criteria for the design of subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
omitted in case of constructed wetlands without free access for members of the
public.
The hydraulic loading for VF CWs in colder climate should not exceed 100 - 120
mm/d and in summer hydraulic rates up to 200 mm/d of pre-treated wastewater
could be applied without negative influence.
Minimum area of each reed bed size 10 m2.
41 Chapter 5: Substrate in Subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
5 Substrate in Subsurface flow CWs
Wetland substrates support the wetland vegetation, provide suitable sites for
biochemical and chemical transformations, and provide sites for storage of removed
pollutants. The different filter media such as soil, sand, gravel, organic materials
which are used in constructed wetlands are known as substrates.
Table 5.1: typical kf values (Cooper et al. 1996)
The provision of a suitably permeable substrate in relation to the hydraulic and
organic loading is the most critical design parameter of subsurface flow systems.
Most treatment problems occur when the permeability is not adequately designed for
the applied load. Some of the horizontal flow CWs which were built from 1985 to
1989 in Europe, used soil as a substrate, where it was assumed that the hydraulic
conductivity would increase. Some of these suffered from surface-flow and this led to
channeling and scouring of the surface which results in areas of the bed being
starved of water and this in turn led to poor reed growth and poor treatment. Similar
problem occurred with plants built in Germany and Denmark (Cooper, 1996).
As a result of these problems, WRc decided in 1986/87 to recommend the use of
gravels in UK system at Little Stretton (Seven Trent Water) and Gravesend (Southern
Water) especially washed gravel of different size like 3-6 mm, 5-10mm and 6-12 mm.
(Cooper, 1996). In Germany with VF CWs with reed beds was built with soil of
hydraulic conductivity of 3x 10-3 m/s and latter it was advised in the European
Guidelines of 1990 (Cooper, 1990) „‟ not to assume a hydraulic conductivity greater
than that of the original media.‟‟ Conventional wisdom regarding intermittent sand
filters suggested clean washed sand with an effective size of 0.2-0.5mm with less
than 1 % by weight passing through a 0.1mm sieve (Reed et al., 1988). At oaklands
Soil Texture kf (m/s)
Fine to course gravel 10-3 - 1
Fine to course sand 10-7 – 10-2
Karst limestone 10-4 – 10-2
Sandstone 10-8 – 10-4
Silt loess 10-9 – 10-5
Glacial till 10-12 – 10-4
Unweathered marine clay 10-12 – 10-9
Shale 10-13 – 10-9
42 Chapter 5: Substrate in Subsurface flow CWs
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Park in UK, VF beds are filled with different layer by graded gravel usually with a top
layer of washed sharp sand as given in table 5.2.
Substrate Depth Size
Top layer
8 cm Sharp sand
15 cm 6 mm washed pea -gravel
10 cm 12 mm round washed gravel
Bottom layer 15 cm 30 – 60 mm round washed gravel
Table 5.2: Graded gravel used in different layer as recommended by Burka at Oaklands Park. (Vymazal et al., 1998)
In additional, large stones were placed around the drainage pipe, which formed the
under drain system. In Austria, substrate profile of VF system was divided into two
major substrate as top and bottom layer. Top layer consists of protection layer of
depth 20 cm filled with 8/16 mm grain size, main layer of depth 60 cm filled with 0/4
and 4/8 mm mixing in 1:1 ration and transitional layer of depth 10 cm filled with 4/8
mm grain size. In the bottom, drainage layer of depth 20 cm filled with 16/32 mm
gravel (Vymazal, 1998).
Similarly in the case of Phytofilt system, beds contains four layer in which top layer of
depth 0.3 m filled with soil ,upper filter layer of depth 0.4 m filled with sand/gravel
having conductivity (kf) value 5.10-3 – 5.10-2 m/s , intermediate filter layer of depth 0.7
m filled with sand /gravel with kf value 5.10-6 – 5.10-5 m/s and lower layer filled up to
0.4 m with kf value 5.10-6 – 5.10-5 m/s. Generally, sand layer needs a thickness of 40
to 80 cm, which has the actual filter bed function of the subsurface flow CWs with a
hydraulic capacity (kf-value) of about 10-4 to 10-3 m/s. The drainage pipes at the base
are covered with gravel and top gravel layer does not contribute to the filtering
process. The recommended grain size distribution for the substrate is like d10 > 0.3
mm or d60/d10 < 4 (Vymazal, 1998). The substrate should not contain loam, silt nor
clay material because of low kf values and hence are not recommended.
Fig 5.1: Example of filter material used in CWs for municipal wastewater treatment in Brazil and Peru (photo by C. Platzer, H.Hoffmann, and source: gtz, 2010).
A B C
43 Chapter 6: Macrophytes used in Constructed Wetlands
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
6 Macrophytes used in the Constructed wetlands
Macrophytic plants provide much of the visible structured of wetland treatment
system. These macrophytes are very important for physical, chemical and microbial
process in the CWs. A basic understanding of the growth requirement and
characteristics of these wetland plants is essential for successful treatment wetlands
design and operation.
Macrophytes have several properties in relation to the treatment process and most
important effects of the macrophytes are the physical effects that plant tissues
prevent the formation of erosion channel, prevent clogging of bed medium, provide
the surface area for attached microorganisms (Brix, 1994a). Similarly plant uptake of
nutrients is only of quantitative importance in low loaded system which is described
detail in chapter 3 (section 3.6) and more focus is given in this chapter about the
transfer of oxygen to the rhizosphere by leakage from root and type of macrophytes
used in CWs. Moreover, macrophytes have additional site specific values such as
providing a suitable habit for wildlife and giving a system an aesthetically
appearance.
6.1 Type of macrophytes used in CWs
A wide range of macrophytic plants occur naturally in wetlands environment and have
been recognized to have the ability to treat wastewater. The United State Fish and
Wildlife Service has found more than 6700 plant species on their list of obligate and
facultative wetland plant species in the United States (Kadlec, 2009). Four groups of
aquatic macrophytes can be used distinguished on a basis of morphology and
physiology (Wetzel, 2001).
Emergent macrophytes: These are the dominating life form in wetlands and
marsches and grow on water-saturated or submersed soils within a water table
ranges from 50 cm below the soil surface to water depth approximately 150 cm or
more. They produce aerial stems, leaves, roots and rhizome-system. These
emergent macrophytes are like Phragmites australis (Common Reed),
Schoenoplectus (Scirpus) lacustris, Typha latifolia (Cattails),
44 Chapter 6: Macrophytes used in Constructed Wetlands
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Fig 6.1: Emergent macrophytes (a) Phragmites australis (b) Schoenoplectus lacustris (c) Typha latifolia (photo –Wikipedia)
Floating - leaved macrophytes: They are rooted in submerged sediments in water
depth of approximately 0.5 to 3 m and possess either floating or slightly aerial leaves
like Nyymphaea odorata, Nuphar luteum(waterlilies), Potamogeton natans (pond
weed).
Freely floating macrophytes: They are not rooted to the substratum and they are
freely floating on in the water surface. These kinds of species are used usually to non
turbulent, protected areas (e.g. Lemna, Spirodella polyrhiza (Duckweed), Eichhornia
crassipes (water Hyacinth).
Submerged macrophytes: These species have their photosynthetic tissue entirely
submerged inside the water surface. Vascular angiosperms (e.g. Myriophyllum
spicatum, Ceratophyllum demersum) occur only to about 10 m of water depth and
nonvascular macroalgae occur to the lower limit of the photic zone (up to 200m, e.g.,
Rhodophyceae).
However, the selection of plant species are required several criteria that are suitable
for use in constructed wetlands under different conditions such as availability in
climate zone, pollutant removal capacity and tolerance ranges, plant productivity and
biomass utilizations. The plants should be selected for constructed wetlands, which
are adapted to the local climate, soil conditions, but also the surrounding plant and
animal communities. A lot of plants that occur in natural wetlands have the potential
for purification of waters as well as higher tolerance capacity. Because, constructed
45 Chapter 6: Macrophytes used in Constructed Wetlands
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
wetlands receive a permanent wastewater inflow including high organic and nutrient
concentrations. All plants cannot tolerate these conditions and will not survive.
Most common macrophytes are popular and recommended for use in constructed
wetlands like Phragmites australis (common reed), Juncus effusus (soft rush) and
conglomeratus, Scirpus lacustris (common bulrush), Scirpus maritimus (alkali
bulrush), Typha angustifolia (narrow-leaved cattail), Typha domingensis (southern
cattail), Typha latifolia (broad-leaved cattail), Iris pseudacorus (yellow flag), Acorus
calamus (Sweet-flag) (Cooper et al., 1996, Vymazal et al., 1998). The emergent
plants most used in constructed wetlands which are survival, tolerance capacity are
given in table 6.1
Table 6.1: Main aquatic macrophytes used in constructed wetlands (Reed et al., 1988) (*- Temperature range for seed germination: roots and rhizomes can survive in frozen soils.)
The hidden objective of macrophytes used in constructed wetlands can be harvested
biomass and can be utilized for energy production, agricultural purposes, animal or
cattle feed, livestock forage, thatching material, diverse handicrafts. Phragmites
australis is one of the most productive, widespread and variable wetland species in
the world. Due to its climate tolerance and rapid growth, it is the predominant species
used in the constructed wetlands not only in Europe but also in tropical and sub-
tropical region (Cooper, 1996). Table 6.2 gives the summary of the typical
characteristics of the main aquatic macrophytes used in CWs.
Emergent species
Temperature Max. Salinity
tolerance mg/l
Optimum pH
Desirable Survival*
Typha 10 - 30 12 – 24 30,000 4.0 – 10.0
Phragmites 12 – 33 10 – 30 45,000 2.0 – 8.0
Juncus 16 – 26 20,000 5.0 – 7.5
Schoenoplectus 16 – 27 - 20,000 4.0 – 9.0
Carex 14 – 32 - - 5.0 – 7.5
46 Chapter 6: Macrophytes used in Constructed Wetlands
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Emergent species
Growth rate
(cover 1st year)
Typical spacing
m
Typical root penetration
in gravel m
Annual
yield (mt /ha) Dry
weight
Habitat value
Typha Rapid dense
0.6 0.3 – 0.4 30 Good nesting cover and food source for
wetlands birds
Phragmites Very rapid
dense 0.6 >0.6 40
Low food values but some values as nesting cover
Juncus Moderate to rapid dense
0.3 – 0.6 0.6 – 0.9 20
Good food source for wetland birds and
nesting for fish when flooded.
Carex Moderate to slow dense
0.15 - < 5
Food source for numerous birds. Good
for habit enhancement.
Table 6.2: Characteristics of main aquatic macrophytes (applied from Cooper et al., 1996)
6.2 Functions of macrophytes in constructed wetlands
The macrophytes growing in constructed wetlands can contribute directly by up
taking nutrient in the treatment processes and indirectly as they support physical,
chemical and microbial processes. The most important effects are the physical effect,
where the presence of vegetation reduces the current velocity, reduces the risk of
erosion, prevent the clogging, increase the water and plant surface area. Similarly,
they provide huge surface area for attached microorganisms and suitable habitat for
wildlife and giving aesthetic appearance for the single house, hotels as well as
floating island. It is well documented that aquatic macrophytes release oxygen from
roots into the rhizosphere. This chapter focuses only about the oxygen release by
macrophytes.
Oxygen release There are many studies which show the ability of some aquatic macrophytes to pass
a supply of oxygen into the rhizosphere through a special helophyte tissue in the
plant stems and roots from the air. The plants, with their roots and rhizomes, provide
the suitable environment for microorganisms‟ growth. Oxygen release rates from
47 Chapter 6: Macrophytes used in Constructed Wetlands
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
roots depend on the internal oxygen concentration, the oxygen demand of the
surrounding medium and permeability of the root wall (Vymazal, 1998).
The ability of macrophytes to transport oxygen and thereby to support of aerobic
microorganism in the rhizosphere is one of the key mechanisms for efficient BOD and
nitrogen removal. The flux of oxygen transferred into the rooting system has been
tentatively quoted to be 4-5 gO2/m2d and later prediction by Armstrong et al., (1990)
based on oxygen release from single adventitious roots plus laterals in a streaming
oxygen –free system, measured polar graphically, yielded 5-12 g O2/m2d; this work
has based on 150 shoots per m2, 10 roots per shoot and a rhizome oxygen
concentration of 17 %. Total flux of gaseous oxygen into the bed substrate of 5.9 g
O2/m2d of which 2.08 gO2/m
2d was through the hollow culms of standing dead culms
of Phragmites australis has been measured Roots and rhizomes used 2.06 g O2/m2d
for the respiration purpose and measured to almost perfectly balance the oxygen
influx through the culms leaving only 0.02 g O2/m2d to be released to the surrounding
matrix. (Brix and Schierup et al., 1990).
Fig 6.2: Oxygen mass balance for Phragmites australis in the constructed reed beds at Kalϕ, April 1988 (g O2/m
2d) (Photo taken: Brix and Schierup, Cooper, Ingenieurbüro Blumberg)
48 Chapter 6: Macrophytes used in Constructed Wetlands
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Individual experiments has been conducted in the laboratory to detect the oxygen
release from roots and rhizomes of Phragmites australis, Typha latifolia, Glyceria
maxima and Iris pseudacorus by using oxygen microelectrodes ( Fruergaard ,1987).
With the help of microelectrode, oxygen concentration within the internal gas-space
of roots and rhizomes was measured by microelectrode penetrating into the root and
rhizome wall. Generally, no release of oxygen from the surface of rhizomes and old
roots could be detected even though the internal oxygen concentration was relatively
high as shown in table 6.3. Only young white roots without laterals released oxygen
to the surrounding medium and it was found that the oxygen release rates were
highest in the sub apical region of the roots and decreased with distance from the
root – apex (Brix and Schierup, 1990). The root –apex itself actually consumed
oxygen from the surrounding medium. However form the experiments of four species,
Phragmites showed the highest oxygen release rate and Typha the lowest. At lower
experiment temperatures the release rates would probably have been higher
because of lower tissue respiration.
Table 6.3: Oxygen release from individual roots of Phragmites, Typha latifolia, Glyceria maxima and Iris pseudacorus measured by an oxygen microelectrode (from Fruergaard, 1987)
Species O2 –release
(10 - 8 g cm-2min-1) Internal O2-con
(vol %)
Phragmites australis
Root apex < 0 Not analysed
2mm from apex 6.3 Not analysed
5mm from apex 4.7 Not analysed
9 mm from apex 4.2 Not analysed
60 mm from apex < 0 Not analysed
Rhizome 0 12.3
Typha latifolia
10 mm from apex >0 10.8
35 mm from apex 0.55 Not analysed
65 mm from apex 0 Not analysed
Glyceria maxima
Root apex < 0 Not analysed
8 mm from apex 1.3 Not analysed
40 mm from apex 2.3 4.7
Iris pseudacorus
Root apex < 0 Not analysed
15 mm from apex 2.0 Not analysed
70 mm from apex >0 5.8
150 mm from apex 0.62 8.5
49 Chapter 7: Scenario of Wastewater Treatment in Nepal
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7 Scenario of Wastewater treatment in Nepal
7.1 Country background
Nepal is a small and beautiful landlocked country lies between two big neighbouring
countries like China on the north side and India on the south, east and west. It is also
known as Himalayan country with total area of 147,181 sq. km (56,827 sq mi) and
divided as per geographically into the three main regions like mountains, hills and
terai regions. Mountains cover 20%, hills fall 63% and terai covers 17% of total area
respectively. It is located between the latitudes 27°42' N and longitudes 85° 19' E
(http://en.wikipedia.org/wiki/Nepal). The altitude varies from some 60 m above sea
level in the terai to 8,848 m the Mt. Everest, which is the highest peak of the world.
Nepal has a population of 29.9 million with an average annual population growth rate
of 1.7 % and life expectancy for males and females is 59 years and 58 years
respectively.Nepal is one of the least developed country with Gross Domestic
Production (GDP) per capita is $ 438 and ranked as low human development
country, at 138 out of 169, with a Human Development Index (HDI) is 0.428 (UNDP,
HDR 2010). The population living below the national poverty line has declined from
42% (1990-1995) to 31% (2003-2004) (www.who.int).
As per the Department of Water Supply and Sewerage (DWSS) under the
Government of Nepal indicates the figure in the period of mid July 2003 to mid July
2007 that 80.4 % of the population have access to drinking water supply and 46 % in
basic sanitation.
Fig 7.1: Map of Nepal showing Mountains, Mid hill and Terai regions (http://www.worldmapfinder.com/De/Asia/Nepal)
China
India
Kathmandu valley
50 Chapter 7: Scenario of Wastewater Treatment in Nepal
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In Nepal, the water resources are regarded having the potential to be the catalyst for
all round development and economic growth of the country. Nepal has a monsoon
type climate. The total rainfall varies between 1,000 to 4,000 mm with an annual
average of 1,814 mm. More than 75% rainfall occurs during four months of the
monsoon period (June - September). Summer temperatures rises more than 40 °C
in Terai and 20°C in hilly region. Similarly in winter, average maximum and minimum
temperatures in the Terai varies from a mild 23°C to a brisk 7 °C while the central
valley‟s experience a chilly 12°C maximum temperature and a minimum temperature
often falling below freezing point. (www.himalayanmart.com)
7.2 Wastewater treatment in Nepal
Wastewater without treatment from household and industry is discharged directly into
receiving the river, which creates serious water pollution problem and so exerts
immense pressure on the urban and semi urban environment. As a result, urban
sanitation has become a major challenge for municipalities and small towns in Nepal.
Wastewater treatment plants are almost non-existent in the country except for a few
in the Kathmandu Valley and outside of valley but even these are not functioning
well. The total wastewater produced in the country is estimated to be 370 million litres
per day (MLD) but installed capacity of wastewater treatment plants is only 37 MLD
fulfilling only 10% of total demand and functioning wastewater treatment plants
account for 17.5 MLD, i.e. 5% of total demand (Nyachhyon, 2006). It is estimated that
only about 12 % of urban households are connected to the sewer system
(www.wateraid.org)
Kathmandu Valley comprises of three districts, Kathmandu, Lalitpur, and Bhaktapur
have total of 150 local administrative units (Village Development Committees and
Municipalities). The Valley encloses the entire area of Bhaktapur district, 85% of
Kathmandu district and 50% of Lalitpur district covering 665 square kilometers and
more than 1.5 million people, (220,000 households) are living. Kathmandu Valley is
the most important urban concentration in Nepal (Pant and Dongol, 2009)
Although there are some waste water treatment systems in Kathmandu Valley (KV),
these are not functional and as a result waste water from the drains and sewers are
discharged directly into the Bagmati, Bishnumati, Dhobi Khola and other small rivers
51 Chapter 7: Scenario of Wastewater Treatment in Nepal
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of KV without treatment. The city is becoming an example of a terribly polluted city
with open sewers and unhygienic disposal of waste leading to the pollution of all the
existing rivers in Kathmandu. (Pant and Dongol, 2009)
7.2.1 Wastewater treatment in Kathmandu Valley
Arata et al., (2003) pointed that only 38 % of the population is connected with the
sewer system and collected 47 MLD of total domestic wastewater (approximately 124
MLD) in Kathmandu valley. According to ADB (2000), there are 1340 industries in
and around the Kathmandu Valley, which generate 0.8 MLD of wastewater. Similarly,
56.7 MLD of wastewater is discharged into the different river systems in the valley,
from which 82% of total volume is of domestic origin.
Within the periods of 1975 -1996, there were five municipal wastewater treatments
plant (WWTP) namely Hanumanghat, Sallaghari, Guheshwori, Dhobighat and Kodku
constructed in the Kathmandu valley for the treatment of wastewater with total design
capacity 34.4 MLD.
Fig 7.2: Map of Wastewater Treatment Plants in Kathmandu Valley (Hillary Green, 2003)
Hanumanghat WTP was constructed in 1975 for 0.5 MLD wastewater treatments
coming from some parts of Bhaktapur city. With the reference of ADB (2000) and
BASP (2002), this plant was under the partial function after the construction but it
was found this plant full of sludge and not working at all, and the land being used as
52 Chapter 7: Scenario of Wastewater Treatment in Nepal
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a crop field (Poh et al., 2003). Sallaghari WTP was designed and constructed in
1983 to treat about 1.0 MLD form north and south parts of Bhaktapur with the support
of the German Government. The system was originally designed as an aerated
lagoon but due to operators cost high cause of electricity cost, aeration system was
closed. Since then, the plant has been partially operating as a non-aerated lagoon
system (Asian Development Bank, 2000).
Dhobighat WTP was designed in 1982 for an average flow of 15.4 MLD wastewater
collected from the northeast part of Kathmandu; however it is not functioning due to
the breakdown of the pump station and truncated sewer line along several sectors in
the city. Lack of proper maintenance, stabilization ponds are now serving as a
grazing for cattle and football field for the local people (Arata, 2003).
Kodku WTP was designed and constructed as stabilization pond in 1982 to treat
wastewater coming from Patan (Lalitpur). This plant consisted of primary anaerobic
ponds followed by secondary facultative ponds with several surface mixers and a
system of mixed, shallow tertiary aerobic ponds (Shrestha, 1999). According to the
ADB (2000), the Kodku system is partially operating, as the chlorinator had never
worked since its installation. According to Tetsuji Arata , MIT Nepal Project team
member, , observed in January 2003 that effluent quality was not satisfactory and
even smelled like that of sewer water when discharged into the Bagmati River
(Green, Poh and Richards, 2003).
Treatment plant
Year of establishment
Capacity (mld)
Type of plant
Area coverage Existing situation
Hanumanghat 1975 0.5 Aerated lagoon
Part of Bhaktapur city
Operating inefficient as non-aerated lagoon
Sallaghari 1983 1.0 Aerated lagoon
North and south part of Bhaktapur city
Operating inefficient as non-aerated lagoon and receives wastewater only from southern part of the city
Guhyeswari 1996 16.4 Oxidation ditch
Northeast ern part of Kathmandu (upper Bagmati zone)
In operation
Dhobighat 1982 15.4 Stabilization pond
Wastewater from the northeast part of kathmandu
Out of oder
Kodku 1982 1.1 Stabilization pond
Part of Patan city
Operating inefficiently
Table 7.1: Condition of wastewater treatment plants in Kathmandu valley (Source: http://www.undp.org.np/publication/html/mdg_NAN/Chapter_8.pdf)
53 Chapter 7: Scenario of Wastewater Treatment in Nepal
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Fig 7.3: Guheshwori Wastewater Treatment Plant. (Photo from Hillary Green, 2003)
Guheshwori WTP was designed and constructed on the bank of Bagmati River in
1996 for the treatment capacity of 16.4 MLD in the upper Bagmati zone especially
treating the wastewater coming from the north part of Kathmandu valley. The main
objective of this project is to keep Bagmati River clean by preventing the direct
discharge of untreated liquid wastes into the river. It is the only fully operating
treatment plant in the Kathmandu Valley than others mentioned four plants above.
The treatment plant adopts the most advanced technology of wastewater treatment
and the process is extended aeration consisting of a deep oxidation ditch of carrousel
type (WHO, 2008). The plant at Guheshwori has two carrousel type oxidation ditches
each with three aerators and 60 HP are required to drive the aerators Operation and
maintenance cost of plant at Guheshwori is estimated 12.5 million NRs/year (US $
167,000 /year) (Richards, 2003).
Although this plant is partially functioning and the cost of operation is very high so
that the sustainability is questionable (Water aid Nepal). It is the possibility of
treatment plant may be halt in the near future, due to the lack of financial support
from the Nepal Government. It is a hotly debated question among wastewater
professionals whether conventional activated sludge wastewater treatment plants are
appropriate treatment technologies suitable for developing countries like Nepal
(Harleman, 2001). These treatment plants are based on simple lagoon systems
except Guheshwori, where wastewater is treated through natural processes such as
sedimentation and biological degradation in a series of large lagoons. Although these
plants are technically very simple with no mechanized parts but they are still not
functioning well because of poor operation and maintenance and mismanagement
54 Chapter 7: Scenario of Wastewater Treatment in Nepal
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7.3 Constructed Wetlands as an alternative technology in Nepal
Most of the centrally collected wastewater treatment plants in Nepal are not
functioning due to high cost of operation and maintenance and lack off trained human
resources. To mitigate the financial problem and minimize of water pollution, low-cost
natural treatment options like Constructed Wetlands (CWs) and the related Reed Bed
Treatment System (RBT) have been introduced in Nepal since 1997.
Environment and Public Health Organization (ENPHO), a national non-governmental
organization, has introduced constructed wetland (CW) as a low cost, simple,
effective and an appropriate alternative technology for wastewater treatment in
Nepal. ENPHO designed and constructed first wetland system with a two staged sub-
surface flow for Dhulikhel Hospital in 1997 to treat domestic wastewater (Shrestha,
1999). Due to the success of the CW system in Dhulikhel Hospital, since then, the
interest of people has been growing in this technology and more than a dozen
constructed wetlands have been established for various applications such as the
treatment of hospital wastewater, grey water, septage, landfill leachate, institutional,
universities and municipal wastewater. Since 1997 to 2004, there are 12 sub-surface
flow constructed wetland systems in operation for treatment of grey water,
wastewater and fecal sludge as shown in Table 7.2
Table 7.2: List of Constructed Wetlands in Nepal (Source: R. R. Shrestha and P. Shrestha)
55 Chapter 7: Scenario of Wastewater Treatment in Nepal
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Recently, ENPHO has established the first community-based wastewater treatment
system in Madhyapur Thimi Municipality of Nepal using this technology with support
from ADB, UNHABITAT, Water Aid Nepal, and Thimi Municipality. Similarly, the
Urban Environment Improvement Project (UEIP) which is being implemented in eight
urban centres with the assistance of ADB is now in the process of constructing 18
more plants in these towns (Water Aid Nepal, www.wateraid.org)
Location TSS
Removal Rate (%)
BOD5 Removal Rate (%)
COD Removal Rate (%)
NH4 Removal Rate (%)
Dhulikhel Hospital
97 97 94 68
Single house grey water
98 98 94 91
Malpi School 97 99 97 97
Sunga Commnunity
98 97 96 85
SKM Hospital 97 98 94 96
Kathmandu University
87 97 93 99
ENPHO 87 95 88 40
Kapan Monastry
99 99 98 96
Table 7.3: Efficiency of CWs (UN-HABITAT, 2008 and ENPHO, 2004)
In general, the performance of the CWs has been excellent as shown in table 7.3.
After regular monitoring of the systems and analysis of wastewater sample shows
high pollutant removal efficiency achieving more than 90% removal of TSS, BOD and
COD. Plant species, which are locally available called Phragmites Karka, is used in
this process.
In Dhulikhel hospital, the designed system does not need any electric energy as the
wastewater is fed hydro-mechanically into the beds. The total cost of the system
including the sewer lines was US$ 27,000 in 1997, while the cost of the constructed
wetland alone was at US$ 16,400 (Poh, 2003). For the single house, the system
required an investment of only about Rs. 36,000 (US$ 520) and the family is able to
save about 400 liters of water per day (Water Aid Nepal). In SKM hospital , the
system also does not need any electric energy as the wastewater is feed hydro-
mechanically into the beds and total costs of the system including the sewer lines
were US$ 27000 in 2000 (Poh, 2003). In Sunga community, the total cost of the
56 Chapter 7: Scenario of Wastewater Treatment in Nepal
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treatment plant was Rs. 2.5 million in which total construction cost of the wetland
amounted to NRs. 1,800,000 (US$ 26,000) at NRs. 2,900 (US$ 40) per m2 of the
wetland and average O&M cost of the wetland is about NRs. 20,000 (US$ 290) per
year. So, Constructed wetlands (CWs) are a biological wastewater treatment
technology designed to mimic processes found in natural wetland ecosystems and
required less land, less expensive for construction, operation & maintenance as
compare to conventional expensive technology. Hence, they can be considered as
effective, economic and environmentally friendly and sustainable systems for
wastewater treatment.
7.4 Fact finding of CWs in Dhulikhel Hospital and Sunga Community
Dhulikhel Hospital is a community-based hospital located in Dhulikhel Municipality
and approximately 30 kilometer far from Kathmandu. Hospital location is 1,650
meters above sea level and has a sub-tropical climate with an annual rainfall of about
1,456 mm (HMG, 1996).Constructed wetlands is designed and constructed by
ENPHO at Dhulikhel Hospital in 1997 as a first plant in Nepal under the technical
support from a Nepali PhD scholar from University of Natural Resource and Applied
Life Sciences, Vienna, Austria (Shrestha, 1999).
The treatment system was originally designed to treat 10 m3 of wastewater per day,
but it is currently treating about 40 m3 per day as the capacity of the hospital has
increased significantly since 2000. The constructed wetland in Dhulikhel Hospital is a
two-staged subsurface flow system, which consists of a horizontal flow bed surface
area of 140 m2, followed by vertical flow bed of area of 120 m2. Three chambered
sedimentation tank of 16 m3 capacity has been constructed for pre-treatment.
Fig 7.4: Site Plan of the Constructed Wetland System at Dhulikhel Hospital (UN-HABITAT, 2008). (Photo by Dr. Roshan Raj Shrestha)
Vertical Flow Bed
Horizontal Flow Bed
57 Chapter 7: Scenario of Wastewater Treatment in Nepal
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The depth of the horizontal bed is found varies from 0.65 to 0.7 meters and filled with
1-4 mm crushed gravel with conductivity (Kf) of 0.03 m/s having pore volume of 39%.
The inlet and outlet zone was filled with 10-20 mm gravel and inlet pipe of 100 mm
diameter PVC pipe with 20 mm diameter hole at a distance of 2 m connected with a
feeding tank (0.9 m3 per feed). The outlet pipe of pipe 100 mm dia. perforated pipe
with 6 mm diameter perforations. Similarly, the depth of the vertical bed is 1.05 m
(0.75m sand, 0.10 m with 5-8 mm gravel, 0.15m with 10-20 mm gravel and 0.05 m
with sand) and filled with clean sand as main layer with conductivity (Kf) of 0.001 m/s
and a pore volume of 30%. The main inlet pipe of 100 mm diameter connected with 6
branches of 50 mm diameter pipe with 8 mm and 6 mm holes at a distance of 1 m.
Both of the beds were planted with Phragmites Karka, a local variety of reeds that
was easily available. The system does not need any electric energy as the
wastewater is fed hydro-mechanically into the beds (UN-HABITAT, 2008). The total
cost of the system including the sewer lines was US$ 27,000 in 1997, while the cost
of the constructed wetland alone was at US$ 16,400.
Initial tests done in 1997 showed that the plant was able to remove 98% of total
suspended solids (TSS), 98% of BOD5, 96% of COD and 99.9% of total coli forms. It
also removed 80% of the ammonia nitrogen and 54% of phosphate. Follow-up
monitoring in 2003 showed that the plant was still removing 96% of BOD5 and 93%
of TSS and COD (Water Aid Nepal Bulletin).
Month Q
m3/day TSS
mg/l NH4 mg/l
PO4-P mg/l
BOD5 mg/l
COD mg/l
E. Coli. Col /ml
IN OUT IN OUT IN OUT IN OUT IN OUT IN OUT
No of reading
13 12 12 11 11 12 12 13 13 13 13 11 11
Minimum 7 26 0.3 17 0.04 2.2 0.6 31 0 63 4 39000 3
Maximum 40 230 6.7 52 5.4 26 18 210 10 1048 40 8E+08 987
Average 20 83 2.3 33 1.6 8 4 110 3 325 20 1E+08 148
Median 11 41 1.8 19 0.04 2 0.7 41 4 79 18 1E+05 38
Std. Deviation
11 58 1.9 12 2.2 7 5.8 63 3 273 14 2E+08 307
Elimination (%)
97 95 47 97 94 99.9
Table 7.4: Summary statistics of inlet and Outlet concentration and mean efficiency Dhulikhel Hospital Constructed Wetland System (1997 to 2000) (Source: Poh, 2003)
The Hospital as well as the local people is very satisfied with the performance of the
treatment system and the system has become a showpiece for the Hospital. Many
58 Chapter 7: Scenario of Wastewater Treatment in Nepal
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researchers, students, journalists and other people regularly visit the Hospital to see
the constructed wetland in action and learn from it. The Hospital is now in the
process of expanding the system.
Sunga community
Madhyapur Thimi municipality, one of Nepal‟s oldest settlements living Newar
community, is a small municipality located in Kathmandu Valley. It has a population
of 47,751 in 2001 and covers a total area of 11.47 sq. km with 20% residential area,
70% agricultural land and around 10% vacant land. As the town was designated as a
municipality only in 1996, major infrastructure developments like the sewerage
system, water supply and road network are all still in the planning phase. Due to lack
of funds, still wastewater treatment through oxidation ponds was not completed;
however a part of the municipality was connected to sewers in the 1990s. From the
social-economic analysis more than 50% of the populations are still lacking proper
sanitation facilities. Sanitation improvement is one of the most urgent issues in the
municipality that should to be addressed, so the local people of Madhyapur Thimi
and the municipality showed an interest in managing the wastewater through
innovative technology.
Fig 7.5: Solid Waste dumping site before and after the construction of CWs at Sunga wastewater treatment plant, Thimi (Photo by: UN-HABITAT and Water Aid/ Marco Betti)
The people of Sunga village are interested to implement the innovative urban
wastewater treatment technology to improve sanitation, improve water quality of
rivers, and provide alternate water uses other than for drinking purposes and to link
with livelihood opportunities for poor communities. At the request of community
59 Chapter 7: Scenario of Wastewater Treatment in Nepal
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people and the Municipality, in 2005, ENPHO, with support from ADB, UN-HABITAT
and Water Aid Nepal, initiated the construction of a community-based wastewater
treatment plant. Sunga constructed wetlands are also known as the first community-
based wastewater treatment plant in Nepal. In addition to the funding agencies,
Madhyapur Thimi municipality provided the required land for construction along with
the financial assistance for operation and maintenance of the wastewater treatment
plant. Under this initiative, ENPHO joined hands with the local people of Sunga and
built CWs on steep terrain, which was previously a waste dumping site near to a
school at Sunga. This treatment plants has come in operation since October, 2005.
Now the site has a beautiful garden and a model treatment plant that provides a
learning ground for students as well as professionals.
The constructed wetland at Sunga consists of a coarse screen and a grit chamber for
preliminary treatment, an anaerobic baffle reactor (ABR) with capacity of 42 m3 for
primary treatment, Horizontal Flow (HF) followed by Vertical Flow (VF) reed beds for
secondary treatment and two sludge drying beds for treating sludge of area 70 m2.
The total area of the constructed wetland is 375 m2 in which HF and VF beds covers
150 m2 by each (UN-HABITAT, 2008). The treatment plant has a capacity to treat
wastewater from 200 households, but it is urgently treating wastewater from 80
households. The plant receives an average daily flow of 10 m3 of very high -strength
wastewater (average BOD5 of raw wastewater is 900 mg/l).
Monitoring of the performance of the system over its first year of operation shows that
it removes organic pollutants highly efficiently (up to 98% TSS, 97% BOD5 and 96%
COD). It was also found that the ABR was very effective in removing organic
pollutants and could remove up to 74% TSS, 50% BOD5 and 18% COD (UN-
HABITAT, 2008). The effluent values show that there is a significant reduction of
BOD5, COD and TSS as compared to the raw wastewater and these values are
below the legal limits (50mg/l TSS , 50 mg/l BOD5 , 250 mg/l COD ) as specified by
the Government of Nepal for the combined wastewater treatment.
The total cost of the treatment plant was Rs. 2.5 million in which the total construction
cost of the wetland amounted to NRs. 1,800,000 (US$ 26,000) at NRs. 2,900 (US$
40) per m2 of the wetland. The average O&M cost of the wetland is about NRs.
20,000 (US$ 290) per year. As per the tripartite agreement made between ENPHO,
60 Chapter 7: Scenario of Wastewater Treatment in Nepal
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the management committee of Sunga WWTP and Madhyapur Thimi municipality, the
municipality has committed Rs 50,000 annually for operation and maintenance
including remuneration (NRs. 3000/month) and equipment for the caretaker. The
average annual O & M cost of the wetland at present is about NRs. 20,000 (US$ 290)
per year, which is less than the amount allocated by the municipality. It has been
agreed that the surplus amount will be transferred to the operation and maintenance
reserve fund for future maintenance of the plant.
(Source: UN-HABITAT, 2008)
By visually observing CWs operation and treatment efficiency, other surrounding
communities of Sunga village are also interested to implement such kind of treatment
plant. During the handover ceremony on 1st September 2006, many other local
communities requested ENPHO to construct additional similar treatment plants in
other parts of the Municipality. These opinions and demands from the local
community clearly indicate that CWs has been well accepted.
The Sunga constructed wetland is a clear demonstration of the effectiveness of the
community based wastewater management project and its contribution. Due to easy
operation and maintenance, this project has many advantages such as treated
effluent from wastewater can be used as multiple purposes like for irrigation,
gardening, toilet flushing, and washing vehicle. In addition, the project has also
become successful in enhancing the river quality and making the treatment plant
healthier and aesthetically attractive with an enhanced environment thus ensuring
benefits to the community dwellers. This has inspired people to adopt this type of
technology that can be managed by the community itself for the solution of currently
mismanaged wastewater in the city.
Table 7.5: Concentration of pollutants at Sunga (August,2006)
Parameter Units RAW ABR HFCW VFCW
TSS mg/l 796 204 28 16
BOD5 mg/l 950 450 165 30
COD mg/l 1438 1188 213 50
Ammonia mg/l 145.5 408.9 214.1 21
Nitrate mg/l 4.1 36.8 32.6 56.6
Total Phosphorus mg/l 26.4 44.3 20.4 24.3
Fecal Coliform CFU/ ml 1.3E+5 1.3 E+6 1.1E+6 8.1E+3
61 Chapter 8: Case Study of Project Area
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
8 Case study of Project Area
8.1 Study area of Gadenstedt
8.1.1 Location
Gadenstedt is a small village lies in the Lahstedt municipality of Peine district situated
in the German Federal State Lower Saxony, south-east of Hanover. The population
of Gadenstedt is annually varying and according to present data total Gadenstedt
population has 2434 (see fig 8.2). The highest point lies in Degree Mountain which is
105.2 m above from sea level and the lowest point 70.2 m above sea level lies in is
Fuhse river south of the „‟ lukewarm Thaler mill „‟ in Gadenstedt.
Fig 8.1: Map of Gadenstedt, Lahstedt (source:http://de.wikipedia.org/wiki/Datei:Landkreise_Niedersachsen.svg and
http://www.maplandia.com/germany/niedersachsen/braunschweig/peine/lahstedt/)
The small river which is called Fuse is flowing near to this small village. The
accessibility of Gadenstedt by bus is 25 minutes from Peine. The village Gadenstedt
is the old communities that can be seen a strong traditional cultural.
62 Chapter 8: Case Study of Project Area
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Fig 8.2: Population graph of Gadenstedt (source: www.lahstedt.de)
8.1.2 Geography and topography
The project area situated in the Gadenstedt of Lahstedt municipality. The
surrounding land of Gadenstedt is flat and used for agricultural purpose. The project
area as per the geographical location lies in 52°14‟48‟‟ north latitude and 10°13‟6‟‟
east longitude. According to the topographic map (1:25000) is the terrain height to 85
meters above sea level.
8.1.3 Climate and hydrology
The annual average temperature and rainfall data are recorded in the metrological
station located in Hildesheim. As per these data, the study area has an annual
average temperature of 9.2°C and annual rainfall 708 mm. However, it was found
maximum temperature of 34°C in July and minimum -4°C in January as per the
recorded data of 2010 at the study area.
8.1.4 Description of the project
Constructed Wetlands has been widely recognized as a simple, effective, reliable and
economical technology compared to several other conventional systems especially
decentralized system of wastewater treatment for rural and semi urban area.
63 Chapter 8: Case Study of Project Area
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Considering this advantage, the municipality of Lahstedt focused to introduce such
kind of technology. The municipal area consists of 43 km2 with 5 villages and a total
of 10.100 populations living in the five villages like Gadenstedt, Adenstedt,
Mündstedt, Oberg, and Groß Lafferde. It was decided to use such kind of treatment
processes however requiring extensive land for constructed wetlands and open
lagoons. This resource is cheaply available in the rural area. The Federal
Government of Germany developed the standard guidelines mentioning the rule and
regulation to treat wastewater according to the population. The treatment of
wastewater is a duty prescribed by the law of government authorities.
The project „‟ Ecotechnological treatment of waste water and sewage sludge in
Lahstedt‟‟ was registered and officially sponsored project at the world exhibition
EXPO 2000 in Hanover. The constructed wetland as polishing biotopes in
Gadenstedt was constructed in 1998 for the waste water treatment covering the area
of 1.1 hectare. After achieving the good results, the Municipality of Lahstedt has
decided to expand and improvement in the sewage plants in the locality of Oberg,
Münstedt, Adenstedt, and Groß-Lafferde.
Fig 8.3: Combined waste water biotope in Oberg
In the 2001 combined wastewater biotopes was constructed in Oberg and Münstedt
covering an area of 0.57 ha and 1.4 hectares respectively. Similarly sewage sludge
processing plant covering an area of 0.6 ha was constructed in Groß-Lafferde in
2002. This is one of the innovative ideas for the alternative system on natural method
is gaining popularity not only in the state of Lower Saxony but also in Europe. This is
64 Chapter 8: Case Study of Project Area
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one of model which show decentralized wastewater treatment under the local level
initiative for the environment protection.
However the main focus is given to waste water treatment through the CWs of
Gadenstedt. The waste water is being treated in Gadenstedt through the combination
of conventional and natural system. The treatment plant is located around 500 m far
in the west side of village. Gadenstedt has an old trickling filter which was
constructed in 1959 and treating the waste water.
Fig 8.4: Isometric view of Gadenstedt and project site (from Google)
An old trickling filter system is also functioning properly but community people are not
interested to replace by new activated sludge systems due to high operation cost.
They are planning to be continuing use of old sewage treatment plant to eliminate the
pollutants from wastewater and will close in near future within the 10 years. After then
they will depend totally upon Constructed Wetland. With the concept of ecological
technology, the project especially designed and constructed in 1998 under the direct
supervision and involvement of Ingenieurbüro Blumberg.
The project was designed with different objective for the wastewater treatment. So
the project was divided into three parts: polishing biotope (reed bed treatment
system); combined waste water biotope (cascade of ponds and reed beds); reed
Gadenstedt
Village
Constructed
Wetlands and
Lagoon area
Screening, Grit chamber,
Trickling filter and Sludge
drying bed
65 Chapter 8: Case Study of Project Area
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
planted dry beds for sewage sludge. A total cost of construction was 1.7 million DM,
whereas Lahstedt municipality shared the cost by 75% and state government of
Lower Saxony by 25 %.
8.1.4.1 Screening
Screening is the first unit operation used at wastewater treatment plants. The main
objective of screening is to remove floating materials like faecal matter, toilet paper
and mineral solids, plastics, stone and metals preventing to damage and clogging of
downstream equipment, piping, and appurtenances. Coarse and fine screens are
used 15-75 mm and 3-12.5 mm.
Fig 8.5: Screening and collection drum (HUBER Screenings Treatment Systems in
Gadenstedt)
A screening compactor is usually situated close to the mechanically cleaned screen
and compacted screenings are conveyed to a dumpster or disposal area. Total 195.7
cubic meter floating materials was screened during the whole year periods, but
values from October and November was not included due to absence of record and
maximum screening material found in January equals to 189.7 cubic meter and
remaining months collected varies from 0.25 to 1.0 cubic meter respectively.
8.1.4.2 Aerated grit chamber
Grit includes sand, gravel, cinder, or other heavy solid materials that are “heavier”
(higher specific gravity) than the organic biodegradable solids in the wastewater.
Screening
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Aerated grit chambers are typically designed to remove particles of 70 mesh (0.21
mm) or larger. When wastewater flows into the grit chamber, particles settle to the
bottom according to their size, specific gravity, and the velocity of roll in the tank.
Aerated grit chamber was designed in a rectangular type to treat around the 400 to
600 m3 per day. It was constructed with the cross section area of 2.5 m2 and the
length of 14 m respectively.
Air is introduced in the grit chamber along one side, causing a perpendicular spiral
velocity pattern to flow through the tank. Heavier particles are accelerated and
diverge from the streamlines, dropping to the bottom of the tank, while lighter organic
particles are suspended and eventually carried out of the tank. Grit is collected from
bottom of channel by automatic sand scraper and pumped into the collecting drum.
Total sand was collected 4 m3 in 2010.
Fig 8.6: Grit chamber in Gadenstedt treatment plant (photo by R. Shrestha, drawing from Ingenieurbüro Blumberg)
8.1.4.3 Trickling filter
Trickling filter was constructed in 1959 and one of the oldest treatment plants
operating to treat the wastewater coming from Gadenstedt village. The trickling filter
was filled with the lava and gravel of sizes ranging from 40 to 80 mm corresponding
with specific surface area of ca. 100 m2 /m3. In the trickling filter the treatment
process proceeds from top to bottom. The lava and gravel are providing more surface
area for the development of biofilms when wastewater flows downwards. The
Gritchamber
67 Chapter 8: Case Study of Project Area
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
removal of pollutants from the wastewater involves both absorption and adsorption of
organic compounds by the layer of microbial biofilms. The BOD5 volumetric loading
rate is found 0.1 kg/ m3.d which is less than 0.4 kg/ m3.d and total nitrogen loading
rate is found 0.039 kg/m3.d which is less than 0.1 kg /m3.d. The surface loading rate
is 4.17 m / d. Under operating conditions ca. 2/3 of this can be assumed to be
biologically active. The depth and diameter of trickling filter consists of 3 m and 13 m
respectively.
Fig 8.7: a) Wastewater dosing into the bed through the rotating arm, b) lay out plan of project, c) trickling filter and d) diagram of biological process in trickling filter
BOD 5
NH4 +
NO3 -
Trickling filter
By R. shrestha From Ingenieurbüro Blumberg
By R. shrestha
68 Chapter 8: Case Study of Project Area
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
8.1.4.4 Constructed Wetland as polishing biotopes
Constructed wetland is used as a tertiary treatment plants like a polishing biotopes
which is used to treat effluent coming from the existing trickling filter. Four vertically
flow CWs was designed and constructed in 1998 covering the total area of 1.1 hector
of which 7300 m2 is covered by reeds (Phragmites) in four vertically percolated CWs.
These ground surfaces are sealed with a lining at bottom to prevent wastewater
entering into the ground water.
Fig 8.8: a) Construction phase of Lagoon, b) Bed preparation of Constructed wetlands, c) planting Reeds in bed during the construction period of 1997-1998, d) after the maturation of Reed
The system was designed to treat 500 m3 / day of the wastewater during summer to
more than 2000 m3 / day in winter. But it was found by data analysis of discharge in
the whole year of 2010 that the actual wastewater treated with varies maximum 650
m3 / day to minimum 496 m3 / day. It was assumed that the treatment capacity would
in the future be extended up to 3000 inhabitants in Gadenstedt. The depth of the
vertical beds is 1.5 meter and filled with different filter materials of different depth
considering as a research purposes (Ingenieurbüro Blumberg, 1998). The area of
a b
c d
From Ingenieurbüro
Blumberg
From Ingenieurbüro
Blumberg
From Ingenieurbüro
Blumberg
By R. Shrestha
69 Chapter 8: Case Study of Project Area
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
constructed wetland is divided into four small reed bed areas and materials used in
these beds are categorized into two groups. Top layer of 10 cm depth was filled with
aggregate and second layer was filled with sand (+ 5% limestone) and aggregate 2/8
mixing in 1:1 ratio in the depth from 10 - 80 cm in the bed 1 & 3. Sand (+ 5%
limestone) and root wood mixing also in 1: 1 ratio was filled in 80 – 125 cm depth and
125 – 135 cm depth with aggregate 2/8. Similarly in bed 2 & 4 are also filled with
limestone 0/32 at depth 0-20 cm, Sand (+ 5% limestone) and without root wood in
depth 20-135 cm. Finally bottom layer of four beds (1, 2, 3, and 4) was filled with
coarse aggregate16/32.
However, there are different filter material used for the purpose of wastewater
treatment with an estimated conductivity (Kf) of 10-4 to 10 -3 m/s and a designed pore
volume of 30-40%. The drained basins are lined with a polyethylene membrane. The
planned freeboard allows storage of a volume up to 2.000 m3 above the filter
substrate. The beds were planted with Phragmites Australis (Common Reed).
Technical data of CWs of Gadenstedt
Total size of area 1.1 hectares Surface Area
Vertical subsurface flow reed beds with total size
7500 m2 Surface area
Depth 1.5 metres
Capacity 3000 P.E Person equivalents
Current connected load 2600 P.E Person equivalents
Hydraulic loading 127 m / yr
Depth Bed 1 & 3 Bed 2 & 4
0-10 cm Aggregate 4/8 Limestone 0/32
10 – 20 cm Sand 0/1 + 5% Limestone } Aggregate 2/8 } 1: 1 mixing
20 – 80 cm Sand 0/1 + 5% Limestone Without Root wood 80 – 125 cm Sand 0/ 1 + 5% Limestone
Root wood } 1:1 mixing
125 – 135 cm Aggregate 2 / 8
135 – 150 cm Aggregate 16 /32 Aggregate 16 /32
Table 8.1: Technical data of Constructed Wetlands at Gadenstedt WWTP
New sewer was constructed from the old sewage treatment plant to the nearby
Polishing biotope. Similarly effluent from trickling filter collected in collection chamber
and pump was installed to distribute wastewater on the polishing biotope (reed beds)
under intermittent loading with a low pressure distribution system. First time samples
were analyzed in 1999 to measure the efficiency of CWs and obtained the good
70 Chapter 8: Case Study of Project Area
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
results as shown in fig 8.9. Constructed Wetlands are used as a tertiary treatment
system.
Fig 8.9: Constructed Wetlands used as a tertiary treatment system
Nonetheless, CWs are also used as secondary treatment of municipal wastewater to
check the efficiency and main objective to replace the trickling filter slowly. The
wastewater was treated through the CWs from December 2001 to April 2002 and it
was found by the analysis that removal efficiency of COD, BOD5 and NH4-N in CWs
were 92%, 96% and 44% respectively. Similarly reduction of TN and TP were found
52% and 29% respectively. Influent and effluent values of organic and nutrients can
be seen detail in fig 8.10.
mg/l mg/l mg/l mg/l mg/l mg/l mg/l
COD BOD5 NO2-N NO3-N NH4-N TN TP pH
Influent 40.0 7.7 0.58 17.2 1.4 19.2 4.5 7.4
Effluent 10.0 4.9 0.035 4.7 0.2 4.90 1.0 7.1
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0First Results in 1999
mg/l mg/l mg/l mg/l mg/l mg/l mg/l
COD BOD5 NO2-N NO3-N NH4-N TN TP pH
Influent 54.0 16.0 0.30 14.0 2.0 16.0 3.0 7.3
Effluent 15.0 4.0 0.10 9.0 0.7 9.00 2.0 7.4
0.0
10.0
20.0
30.0
40.0
50.0
60.0
October 2004 - Setember 2005
n = 50
n = 20
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Fig 8.10: CWs used as secondary treatment system at Gadenstedt WWTP
8.1.4.5 Combined waste water biotope
First of all, domestic wastewater and rain water from paved surfaces area of
Gadenstedt flow together through the combined sewer system into the treatment
plants. During heavy rains a considerable amount of such combined wastewater is
diverted into the open lagoons before entering to the treatment plants. Combined
wastewater biotopes are used to treat large amount of wastewater coming from
paved surface during the rainy season and protected the receiving river being
polluted from organic and inorganic pollutants. This lagoon system was designed to
treat wastewater 123000 m3 per year and 19250 kg COD per year from 38.5 hectare
paved area.
Fig 8.11: Combined wastewater treatment biotope (Lagoon) at Gadenstedt WWTP
mg/l mg/l mg/l mg/l mg/l mg/l mg/l
COD BOD5 NO2-N NO3-N NH4-N TN TP pH
Influent 301.0 165.0 0.60 9.8 13.4 22.1 4.1 7.5
Effluent 24.0 4.0 0.10 3.1 7.5 10.70 2.9 7.3
0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
December 2001 to April 2002
n = 19
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Combined wastewater biotopes of total area covering of 17000 m2 are divided into
three parts, which are called settling pond, unaerated storage pond and reed planted
soil filter. Wastewater is first passed though settling ponds with covering area of 2940
m2 to settle the suspended solids and after then treated in retention pond where
organic pollutants are oxidized by aerobic and anaerobic process. Storage pond has
a covering the area 5070 m2 with a large retention capacity of 13440 m3 and
detention volume of 4680 m3.
Floating islands are also constructed in the storage pond. Marsh plants growing on
floating islands accelerate the sewage purification process and absorb noxious
substances and nutrients dissolved in the waste water. The root zone under the
water provides a suitable place for the growth of microbiofilms (e.g. fixed nitrifying
bacteria). The wastewater is finally treated in a reed planted soil filter covering net
area 1.330 m2 before it is discharged into the receiving river Fuhse.
Gadenstedt
Total size 1700 m2 Surface area
Settling pond 2940 m2 Surface area
Retention pond 5070 m2 Surface area
Permanent retention volume 4680 m3 capacity
Maximum volume of water 13440 m3 capacity
Storage volume 8760 m3 capacity
Reed bed filter 2400 m2 Total Surface area
Hydraulic load on Reed bed filter 132 m/ yr
Table 8.2: Facts and figures about the combined wastewater treatment biotope
(Source: Ingenieurbüro Blumberg, Leaflet of Lahstedt Municipality)
The former method of combined waste water treatment in Gadenstedt did not
conform to legal requirements. The permissible pollutant overflow rate of 250 kg COD
/ ha / yr was clearly exceeded with a figure of 372 kg COD / ha .yr. The specific
overflow load will be below 64 kg COD / ha /yr well within the limit in Lower Saxony.
Samples were taken from December 2001 to April 2002 to analyze the concentration
of organic matter and nutrients. This system is therefore far superior in efficiency to
conventional combined waste water treatment systems with concrete basins.
Construction and maintenance costs are clearly lower. Hydraulic stress impacts on
the receiving river are avoided. A secondary environmental complex with valuable
biotope functions is established.
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Figure 8.12: Isometric view of wastewater treatment plant at Gadenstedt
8.1.4.6 Sewage sludge dewatering and mineralization in reed beds
Sewage sludge is the end product of wastewater which is settled in the primary
settling tank and pumped into the reed beds for dewatering and mineralization
process where such kind of sludge is treated with aerobically and anaerobically. This
scarcely known method of dewatering and stabilizing sewage sludge in dry beds
planted with reeds has been in practice in Gadenstedt for nine years. Three reed
beds are used for this purpose covering area of 516 m2 .The roots of the plants which
penetrate the dumped sludge helps to accelerating the dewatering and mineralization
process.
Dewatering process is achieved by evapotranspiration and especially by drains which
are fitted at the bottom of the reed beds. Dry bed also helped in reduction of
pollutants in sewage sludge. It was found that sewage sludge dewatered and
stabilized in the reed beds which are designed for operation approximately 10 to 15
years with energy saving method and after then beds are cleared and refilled with
sludge for the next 10-15 years. However, from the experienced showed that dry
Source: Ingenieurbüro Blumberg
website (http://www.blumberg-
engineers.de/)
Common Reed
in CWs
74 Chapter 8: Case Study of Project Area
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matter content of over 50 % is currently achieved. The major advantages of dry reed
beds are to store surplus sludge load during the winter months when agricultural use
is prohibited. Transport costs are lowered by volume reduction and new options for
utilization and recycling of this valuable nutrient source in landscaping, horticulture,
tree nurseries, private gardening and recultivation can be explored. It is one of the
natural sludge dewatering and stabilization at reasonable investment and
maintenance costs.
8.1.5 Method and Field works
8.1.5.1 Field work - pH measurement
It is very important to measure the pH value of influent and effluent of waste water
because of the pH value shows the characteristic of water whether it is an acidic or
basic. Pure water is said to neutral with a pH value close to 7.0 at 25 °C. Influent and
effluent of wastewater with a pH lesser than 7 are said to be acidic and a pH greater
than 7 are basic nature. It is measured on a scale of 0 to 14. The term pH is derived
from “p” the mathematical symbol of the negative logarithm (base10) and “H” the
chemical symbol of Hydrogen. The formal definition of pH is the negative logarithm of
the hydrogen ion concentration i.e. pH = -log10 [H] +.
pH variation is dependent upon the hydrogen ions concentration. When hydrogen
ions concentration is low, pH indicates high and water becoming more basic. Water
with low pH cause the acidic or high pH cause basic nature is harmful to the flora and
fauna. Most organisms have adapted to life in water of a specific pH and may die if it
changes even slightly. This is especially true for aquatic life. The most significant
environmental impact of pH involves synergistic effects. Synergy involves the
combination of two or more substances which produce effects greater than their sum.
Changes pH value of water shows the negative impact on the quality of the receiving
river and soil properties. So pH is a critical factor determining the health of a
waterway. pH measurement is important for environmental science, civil engineering,
food science and many other applications.
In addition to controlling various biological processes, pH is also a determinant of
several important chemical reactions. Ammonium changes to free ammonia at pH
75 Chapter 8: Case Study of Project Area
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above neutral and at higher temperature. The protonation of phosphorus changes
with pH and the hydroxide and oxyhydroxide precipitations of iron, manganese and
aluminum and pH sensitive. (Kadlec und Wallace, 2009)
Limiting pH Values
Minimum Maximum Effects 3.8 10.0 Fish eggs could be hatched, but deformed young are often
produced
4.0 10.1 Limits for the most resistant fish species 4.1 9.5 Range tolerated by trout --- 4.3 Carp die in five days 4.5 9.0 Trout eggs and larvae develop normally 4.6 9.5 Limits for perch --- 5.0 Limits for stickleback fish 5.0 9.0 Tolerable range for most fish --- 8.7 Upper limit for good fishing waters 5.4 11.4 Fish avoid waters beyond these limits 6.0 7.2 Optimum (best) range for fish eggs --- 1.0 Mosquito larvae are destroyed at this pH value 3.3 4.7 Mosquito larvae live within this range 7.5 8.4 Best range for the growth of algae
Table 8.3: Limiting pH values for different aquaculture (Source: CWQRB, 1963)
A pH meter is used to measure the pH
value of water. It is an electronics
instrument consist of a glass electrode
connected to an electronic meter which
helps to measure pH by the activity of
hydrogen ions nears it tips and displays
in digitally on the electronic meter. Three
pH values are measured every day in
the morning and sometimes afternoon
by using pH meter and recorded for the
data analysis. Firstly, pH value of influent waste water is taken at Grit chamber before
entering to the trickling filter. Second measurement is done on the effluent water from
Trickling and third measurement on the effluent coming from constructed wetlands.
Daily measured values of pH are recorded in the dairy by manually. It was found that
pH meter was kept in a wet condition when it was not used to prevent the glass
electrode being dehydrated and cleaned once in a month by using HCl.
Figure 8.13: pH meter (WTW pH 315i)
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8.1.5.2 Temperature measurement
Daily meteorological variations in air temperature, cloudiness, windiness and relative
humidity cause responses in the water temperature changes. The annual cycle of
wetland water temperatures follows a sinusoidal pattern with summer maximum and
minimum in winter. Kadlec and Wallace et al. (2009) pointed out four reasons for the
importance of water temperature in treatment wetlands like several key biological
processes, water quality parameter, evaporative water loss processes and functional
in subfreezing conditions even in cold-climate. Several biogeochemical processes
that regulate the removal of nutrients in wetlands are affected by temperature, thus
influencing the overall treatment efficiency (Kadlec and Reddy, 2001). The
temperature conditions in a wetland affect both the physical and the biological
activities in the system. The biological reactions responsible for BOD removal,
nitrification, and denitrification are known to be temperature dependent (Reed et al.,
1995). In the studies highlighted above, it is reasonable to expect temperature to be
significant in wetlands treating the waste water.
To analysis the temperature effects on the biological activity, daily air temperature of
maximum to minimum was recorded by automatic temperature reading equipment
installed in the site and similarly water tempera was also measured by a pH meter
together during pH reading. Daily water temperature is recorded in daily record book
by manually.
8.1.5.3 Sample collection for COD, BOD, NH4-N, TN, TP analysis
Field work Water sample were taken for chemical / physical and biological analysis from three
different places of treatment plants. Water sample were taken from the site using
1000 ml bottle washed with a 2 percent HCl solution and rinsed with distilled water.
Rinsing with acid and distilled water is necessary to remove any contaminant present
in the bottle. The samples were collected mostly in the morning time and once in a
week. Actually sample collection was done four times in every month for physical and
chemical analysis but sometimes found to be 5 to 6 times in a month. There are
always five to six days differences between each start of new sample collections.
77 Chapter 8: Case Study of Project Area
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Fig 8.14: Influent and effluent sample taken at Gadenstedt WWTP
First influent sampling was taken near to grit chamber and second sample taken
effluent of trickling filter and third was taken effluent of constructed wetlands. More
priority was given sample collection and handling so samples were always deliver to
Laboratory within two hours of last sampling time. It was always kept in mind that if
analysis was not started within two hours, sample should be kept at sample container
below 4 °C from the time of collection. All samples were stored in a dark insulated
box until the return to the laboratory.
Sample were analyzed for COD, BOD5, total Nitrogen (TN), and total phosphorus
(TP) and nitrogen in the form of nitrate (NO3-), nitrite (NO2
-) and ammonia (NH4-N).
Mitsch et. al., (1998) explained that samples, if not analyzed immediately after
collection, were preserved with concentrated H2SO4 and refrigerated for later
analysis. Sample preservation or analysis was completed within 48 hours of
collection.
Lab procedure There is central laboratory located in Groß-Lafferde, where samples ware brought for
the experiment of COD, BOD5, NH4-N, NO3-N, TN and TP from different treatment
plants situated in Lahstedt municipality like Lahstedt, Oberg, Adenstedt, Münstedt
and Groß-Lafferde. In the Lab, wastewater sample was tested by the HACH LANGE
cuvettes test method and this method being much easier, saves space, time and high
efficiency of achieving the reliable data. The method is also known as „‟ operational
analytical method‟‟ and is an alternative to reference DIN method. The sample after
collecting in Gadenstedt treatment plants is returned into the laboratory within the 45
78 Chapter 8: Case Study of Project Area
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minutes and sample analyses are conducted. The results obtained by this method
are verified by water authority of Peine four times in a year.
Fig 8.15: left: Sample of wastewater in the Laboratory for the analysis .Right: Miss Katharina Ohlemann (Lab technician) using the Homogenizer to homogenize the sample.
Biochemical Oxygen Demand (BOD5) Biochemical oxygen demand represents the amount of oxygen consumed by bacteria
and other microorganisms while they decompose organic matter under aerobic
conditions at a specified temperature. The Biochemical Oxygen Demand in 5 days is
of the sum parameter for the assessment of organic and oxidatively degradable
wastewater pollution. In the operational analytical method, LCK -555 Cuvettes test is
used to analysis BOD5 considering the recommended concentration on the range of
4-1650 mg / l. BOD5 is measured with referring to the Hack Lange booklet3.
First, dilution water was made with reference to the Dr. Lange booklet. Wastewater
sample is homogenized with the help of homogenizer within 30 seconds, which rotate
20000 rpm. Wastewater sample are screened by filter paper and filled into three
cuvettes by opening DosiCap Zip. Reagents (tablets and beads) is poured into
cuvettes with the help of funnel and sealed immediately after funnel is removed and
there should not be air bubbles inside the sample cuvettes. Repeatedly invert the
dilution water and sample cuvettes for 3 minutes until the reagent tablets have been
3 LCK cuvettes method can be found in the internet online for more information in the website
http://shop.hach-lange.com
79 Chapter 8: Case Study of Project Area
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dissolved completely.
After then, the three cuvettes are filled with
required amount of sample and dilution water as
per the table 8.4, using a transfer pipette, ensuring
there are no air bubbles, and seal with the DosiCap
Zip. First cuvettes are filled with 1 ml sample of
influent and 3 ml dilution water considering the
BOD5 measurement ranged 50 – 275 mg /l under
the category of B2. Second and third cuvettes are
filled with 4 ml of sample taking the effluent of
trickling filter and constructed wetlands considering
the low BOD5 concentration under the category A1.
These samples are shaken vigorously for 1 minute
in order to enrich the sample with oxygen and leaved in darkness in the block
thermostat maintaining the temperature at 20°C for 5 days. After the 5 days, cuvettes
are evaluated by photometry, this shows directly the BOD5 in mg/l O2 and data are
recorded as concentration of BOD5 in inflow and out flow of wastewater.
Measuring range
Preliminary dilution in reaction tube
Prepared sample
Dilution factor
(mg/l) Sample Dilution water
Pipette into the cuvette test
For CADAS 200 / LASA 30/50/ 100 / XION 500
A = 4 – 58 A1 = 4 – 19 A2 = 7 – 38 A3 = 11 – 58
4 ml 4 ml 4 ml
- - -
1.8 ml 0.9 ml 0.6 ml
3.5 7.0 10.5
B = 25 – 413 B1 = 25 -138
B2 = 50 – 275 B3 = 75 – 413
1 ml 1 ml 1 ml
1ml 3 ml 5 ml
0.5 ml 0.5 ml 0.5 ml
25 50 75
C = 100 – 1650 C1 = 100 – 550 C2 = 200 – 1100
C3 = 300 -1650
0.4 ml 0.4 ml 0.4 ml
2.8 ml 6.0 ml 9.2 ml
0.5 ml 0.5 ml 0.5 ml
100 200 300
Table 8.4: Sample preparation as per upper limit of measuring range of BOD5
(http://shop.hach-lange.com/shop/action_q/download)
Fig 8.16: SPECTROPHOTOMETER
DR2800 for the measurement of BOD5
and other required data also in Groß-
Lafferde
80 Chapter 8: Case Study of Project Area
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Chemical oxygen demand (COD) COD is used to measure the oxygen equivalent of the organic material in wastewater
that can be oxidized chemically using potassium dichromate – sulphuric acid solution
in the presence of silver sulphate as a catalyst. Chloride is masked by mercury
sulphate. The green coloration of Cr3+ is evaluated (www.hach-lange.co.uk).
Fig 8.17: COD measurement of LCK-514, LCK-314 cuvettes kits box and HT200S high temperature Thermostat.
For the COD analysis, Hach - Lange method was followed and selected the LCK -
514 cuvettes test for the inflow wastewater sample considering the COD
concentration range 100 – 2000 mg/l O2 and LCK – 314 cuvette test for the effluent
water with low COD concentration ranging 15 -150 mg/l. Three cuvettes is taken and
filled with 2 ml sample water, initially homogenized with the help of homogenizer and
screened with filter paper. After closing the cuvettes and thoroughly cleaned the
outside, cuvettes are inverted for few times and put into the thermostat for heating
these sample at a temperature 170 ° C for 15 minutes instead of heating at 148°C for
2 hours. When the heating process is completed then hot cuvettes are taken out and
immediately inverted two times after the lock opening of thermostat. These sample
cuvettes is put again in thermostat for cooling down at room temperature (18-20°C).
It is also important to see that sediment must be completely settled before evaluation
is carried out and clean the outside of the cuvette. Cuvettes are evaluated by
spectrophotometer, which shows directly the COD concentration in mg / l O2 of inflow
and out flow of wastewater sample.
81 Chapter 8: Case Study of Project Area
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Total Nitrogen (TN) Total nitrogen of wastewater was also analysis by LCK – 338 cuvette test as per the
Hach –Lange method and process taken into eight steps. First of all, 0.2 ml sample
was put into the reaction tube and poured the reagents of 2.3 ml solution A and 1
tablet reagent B, whereas A indicate the sodium hydroxide solution and B represents
oxidant tablet. Then reaction tube is
closed immediately and put in the HT
200S thermostat at the temperature
170°C for 15 minutes. After cooling down
the reaction tube into room temperature
(18-20°C) in which 1 micro cap C
reagents is added and inverted a few
times until the streak are vanished. Such
digested sample of 0.5 ml from reaction
tube is filled slowly into the cuvettes test by
pipette and 0.2 ml of D solution reagent is
mixed. Then cuvettes tests are quickly closed and inverted few times until no more
streaks can be seen. After 15 minutes, outside of cuvettes are thoroughly cleaned
and measured the total nitrogen in mg/l O2 by spectrophotometer DR2800. The total
nitrogen compounds are known as the sum of the Kjeldahl-N + NO2-N + NO3-N.
Total phosphorus Total phosphorus was analyzed LCK - 348 cuvette test method. Firstly foil is removed
carefully from the Dosi Cap Zip of cuvettes and opened the Zip, after then filled 0.5
ml sample into the three cuvettes. The Dosi Cap Zip is tightened and shaken the
cuvettes firmly and put these sample into the thermostat for standard heating at
temperature 170°C for 15 minutes. After cooling then mixed 0.5 ml reagent B and
screwed by a grey DosiCap C onto the cuvettes. Cuvettes are inverted for few times
and after 10 minutes also inverted a few times more afterwards thoroughly cleaned
outside of the cuvettes. Finally Cuvettes are put into the spectrophotometer which
displays the concentration of total phosphorus in sample in mg/l.
Fig 8.18: Total nitrogen (TN) measurement of LCK-338 cuvettes kits box with reagents (A, B, C and D)
82 Chapter 8: Case Study of Project Area
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Ammonium - Nitrogen (NH4-N) The main principle of measurement is ammonium ions
react at pH 12.6 with hypochlorite ions and salicylate
ions in the presence of sodium nitroprusside as a
catalyst to form indophenol blue. In the laboratory,
NH4-N is analyzed very simple and quickly way by
LCK -303 cuvettes test as per described by Hach-
Lange method. Firstly foil is removed carefully from
the DosiCap Zip and opened the cap. In the three
cuvettes, 0.2 ml homogenized sample is filled with the
help of pipette and quickly closed by DosiCap. After
cuvettes are shaken 2- 3 times and kept in rest. After
15 minutes, outside of cuvettes are thoroughly
cleaned and kept in spectrophotometer which displays
the concentration of ammonium nitrogen (NH4-N) in
sample in mg/l.
Fig 8.19: LCK-303 cuvettes test sample for NH4-N and Kit box with instruction of measurement process.
Nitrate - Nitrogen (NO3 - N)
In the laboratory, nitrate nitrogen (NO3-N) is analyzed very quickly by LCK -340 and
LCK- 339 cuvettes test method. In LCK -340 cuvettes test is conducted considering
the concentration of NO3-N high in influent sample in the range of 5- 35 mg/l and
LCK -339 cuvettes test for the NO3-N concentration low in effluent of sample within
the range of 0.23 – 13.5 mg/l.
First test sample is prepared as LCK-340 test method by filling 0.2 ml sample into the
cuvette and mixed 1.0 ml the reagent A solution. Similarly second test sample
prepared as LCK-339 by filling the cuvette with 1.0 ml sample and mixed with 0.2 ml
solution A reagent. After then both cuvettes are closed and inverted a few times until
no more streaks can be seen in the sample. Cuvettes are cleaned thoroughly after 15
minutes and evaluated with the help of spectrophotometer which displays digitally the
concentration of nitrate - nitrogen (NO3-N) in sample in mg/l.
83 Chapter 8: Case Study of Project Area
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Fig 8.20: LCK -340 and LCK -339 cuvettes kit boxes for NO3-N measurement
Nitrite-Nitrogen (NO2-N) Nitrite is tested in the laboratory by the LCK -342 cuvettes test method. Considering
nitrite nitrogen concentration in the wastewater sample should be low as within the
range of 0.6 – 6.0 mg/l. This analysis is also similar to previous described method of
NH4-N and NO3-N. Three cuvettes is filled with 0.2 ml sample for the test and
immediately closed by the DosiCap. The cuvettes are shaken 2-3 times with firmly
then kept in rest for 10 minutes. After then cuvettes are again inverted few time and
cleaned outside surface of cuvettes. Finally, cuvettes are evaluated with the help of
spectrophotometer which displays digitally the concentration of nitrite - nitrogen
(NO2-N) in sample in mg/l.
8.2 Study area of Berel
8.2.1 Location
Berel is one of the very small village of Baddeckenstedt municipalities and situated in
Wolfenbüttel district (Lower Saxony). This small village lies 20 km south of Peine, 21
km east of Hildesheim and 11 km west of Salzgitter. The Population of Berel was
found from 1996 to 2003 on average 684 inhabitants, (1999 Max 698 inhabitants and
2003 Min 668 inhabitants).
84 Chapter 8: Case Study of Project Area
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Fig 8.21: Map of Wolfenbüttel district and Berel (Source: http://commons.wikimedia.org/wiki/File:Landkreise_Niedersachsen-en.svg And http://maps.google.de/maps)
8.2.2 Geography and topography
The project area is situated in the Berel of Baddeckenstedt municipality. The
surrounding land of Berel is flat and used for agricultural purpose. The project area
as per the geographical location lies in 52°9‟54‟‟ north latitude and 10°13‟4‟‟ east
longitude. According to the topographic map, this village is 167 meters high from the
sea level.
Fig 8.22: Geographic location of Berel (Source: http://maps.google.de/maps )
52 °9‘ 54‘‘ N
10°13‘ 4‘‘ E
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8.2.3 Description of the project
Wastewater was treated by a pond plant system in Berel since 1989; the plant was
originally designed to be naturally ventilated type, consisting of three successive
ponds. After waste regulation system was designed for 600 residents of the Great
Class 1 (<1,000 inhabitants). Village has its own separate sewer to carry out
wastewater coming from private house and rain water from paved surface. The
wastewater is discharged through sewer pipe from the village to the existing pond
treatment plant under the gravity flow system. The treatment plant is located around
600 m southeast of the village at an altitude of about 167 m above sea level. The
site is bounded on the south side of the receiving water Sangebach.
Fig 8.23: View of Berel village and treatment plant (Source: http://maps.google.de/maps)
By 1996, wastewater was treated and purified by pond under the natural system and
found under the legal requirement. After then final effluent values of pond are not
found under the legal limit described by Wolfenbüttel district. It was found the oxygen
deficiency and bad odor. For the better quality control and reduction of COD, BOD
and nutrients in wastewater, two mobile surface aerators have been used in the pond
- 2 since 1996. After then the effluent values were measured from 2004 to 2006 as
shown in fig 8.24 and 8.25, the results also showed the concentration of COD, BOD
and Ntotal were more than legal limit described by Wolfenbüttel. Wolfenbüttel district
Berel village
Berel WWTP
plantplant
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recommended the limiting values of COD, BOD5, TN, TP concentration before
discharging into the receiving water course Sangebach are shown in Table 8.5
Monitoring values of the district Wolfenbüttel
Chemical oxygen demand (COD)
100 mg /l
Biological oxygen demand (BOD)
40 mg /l
Phosphor (P total) 8 mg/l
Nitrogen (N total) 40 mg/l Table 8.5: Requirements for waste water at the point of discharge into the Sangebach
Fig 8.24: COD and BOD effluent values of self-monitoring of the treatment plant Berel
Fig 8.25: Ntotal and Ptotal effluent values of self-monitoring of the treatment plant Berel
87 Chapter 8: Case Study of Project Area
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From 31.01-19.03.2003, around 45 days, the Water Association of Peine investigated
the hydraulic conditions of the sewage system around the catchment area of Pond
treatment plant. The assessment of the external water inputs to the sewage system
was based on the specific water consumption and population of 668 inhabitants.
Total wastewater volume runoff into the sewer pipe was measured 5952 m3 during 45
days in which average water consumption was by inhabitants was 3607 m3
This showed that the difference 2345 m³ wastewater was entered into the pipe from
outside. The external water share was limited to 65% of the waste water runoff.
Regarding the flow characteristics, the low rainfall condition was also observed
during the investigation period. Water Association Peine was concluded that the
more external water into the sewer pipes due to improperly connected drains and
leaky channel coverage layer and ground water discharging into the sewage system.
Community people were interested to improve the water quality as per the required
limit and upgrading the sewage treatment pond safely through constructed wetland.
The project especially was designed and constructed in 2008 under the direct
supervision and involvement of Ingenieurbüro Blumberg. The project cost was
541,830.00 Euro.
8.2.3.1 Screening
Screening is the first unit operation used at wastewater treatment plants. The main
objective of screening is to remove floating materials like faecal matter, toilet paper
and mineral solids, plastics, stone and
metals preventing to damage and clogging
of downstream equipment, piping, and
appurtenances. The Screen system in the
influent of the Berel treatment plant is
designed as a flat fine screen with a gap
width of 3 mm. Because of the relatively low
feed rate to the treatment plant, the
smallest size is provided by the company
Grimmel Water Technology (or equivalent)
The maximum hydraulic capacity of the
Fig 8.26: Screening and automatic
screening waste collected in
dust pin at Berel WWTP
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proposed computer system provides a adequate security for future new connections
to the sewage treatment plant in Berel.
Technical data of Screening system
Wastewater supply Q max 10 l/s
Channel width W 500 mm
Channel depth 600 mm
Bar rack width 460 mm
Bar gap width 3 mm
Maximum water level before screening H 200 mm
Machine height from channel bottom 1360 mm
Machine width 800 mm
Machine length 1650 mm
Electrical power around 4.5 kW
Table 8.6: Technical data of screening system installed in Berel
8.2.3.2 Pond system
The treatment plant in Berel was designed in the late eighties as a naturally aerated
pond treatment system. The treatment plant consists of three successive lagoons
with a total surface area of 6,800 square meters. The surface ratio of the ponds is
around 4:3:3. The largest pond 1 has a surface area of 2,700 square meters.
Structurally, the lagoons have been designed with a slope gradient of 1:1.5, a depth
of 1.20 m and a freeboard of 20 cm. The inflow into a pond branches off from the
shaft 109 and terminates in an inlet structure as shown in fig 8.27. In pond 1, a mud
pocket and a floating baffle wall were installed. Baffles walls were constructed in
ponds 1 and 3 to allow the flow through the entire treatment plant. The overflow of
the ponds and the drainage area to the receiving waters consist of a landscaped area
of shallow water depth of 20 to 50 cm with embankment slope 1:1.6. Overflow and for
the period of sludge removal from Pond 1, wastewater is diverted directly from
manhole No. 109 to pond 2 through the manhole No. 110 as shown in fig 8.27
Fig 8.27: Isometric view of Berel WWTP and settling pond
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Wastewater was first treated through a combination of physical, biological, and
chemical processes in the pond1, also known as settling pond, where suspended
solids settled and organic material is decomposed by aerobic bacteria under the
biological reaction to reduce the COD, BOD. After then wastewater is pumped into
the constructed wetland. Effluents from constructed wetlands enter the pond 3, which
is working as polishing pond. Finally effluent of polishing pond is discharged into the
receiving small river called Sangebach. For the efficiency of pond system is
described more detail in chapter 9 (result and discussion).
8.2.3.3 Constructed Wetlands (CW)
Constructed wetlands are designed in Berel for a maximum treatment capacity of 600
residents. The calculation and design of CWs is based on the DWA Worksheet A 262
(2006) and the design of the FLL / IÖV worksheet "recommendation for planning,
construction, care and maintenance and operation of constructed wetlands"
2005/2006. Total surface area of constructed wetland is 2400 sq.m and divided into
four equal small reed bed areas having each surface area of 600 sq.m .
Fig 8.28: a) Gravel filling over the drain pipe in the bottom layer of bed, b) Reed planting in the bed, c) Lay out plan of Berel treatment plant (Pond and constructed wetlands) d) Reed after the maturation, e) End cape fitting at distribution pipe
The total depth of the vertical flow beds is 1.0 meter and filled with different filter
materials of different depth (Ingenieurbüro Blumberg, 2006). At the bottom layer,
By Ingenieurbüro Blumberg
By Ingenieurbüro Blumberg By Ingenieurbüro Blumberg
a
b c
d
e
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where HDPE drain pipe were laid down
to drain water, was filled with coarse
aggregate of 16/32 mm size up to 0.25 m
depth. Second layer was also filled with
fine aggregate of 5,6/8 mm size up to
0.15 m and top layer of about 0.60 m
depth was filled with fine sand filter
materials. Figure 8.29: shows the structure of the filter
materials used in CWs schematically.
Phragmites communis (common reed) was planted on the surface area of CWs.
Two pumps were installed to deliver controlled amounts of the waste water
intermittently and alternately on the four beds of CWs. The distribution of the waste
water to the four reed bed is controlled by four electrically operated valves.
Wastewater is evenly distributed on the surface through a feed system of HDPE
pipes with low pressure largely maintenance. Possible blockages can be washed out
by removing the end caps of distribution pipes. Bed slope was maintained about 2%
to drain water under gravity system and percolated water was collected by drainage
pipe. These pipes are also connected with main drainage pipe (DN 200) and
collected into the collection chamber after then discharged directly into pond 3.
8.2.4 Method and Field work
8.2.4.1 Field work
At Berel treatment plant, water samples were collected mostly once a week in the
morning time and totally four times in a month for better result analysis. Actually
samples were taken for Lab analysis from four different places of treatment plants
and collected in 1000 ml plastic bottle separately. First influent sampling was taken
near to inlet of settling pond, second sample taken effluent of settling pond, third was
taken effluent of constructed wetlands (1 and 2) and fourth sample was final effluent
of polishing pond. All samples were stored in a dark insulated box until the return to
the laboratory. In Labor, Sample ware analyzed for COD, BOD5, total Nitrogen (TN),
and total phosphorus (TP) and nitrogen in the form of nitrate (NO3-), nitrite (NO2
-) and
ammonia (NH4-N).
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Fig 8.30: Water sample collection as shown in circle at Berel treatment plant
A pH meter is used to measure pH value of water, which help to find out whether it is
acidic or basic or neutral nature and with together ph reading, temperature reading is
also recorded. A pH meter is an electronics instrument which displays pH and
temperature values in digitally on the electronic meter after the glass electrode
dipping into the sample and hold at least 60 seconds. Water temperature and pH
values are recorded by manually, when the sample is collected for Laboratory
analysis.
8.2.4.2 Laboratory work
There is branch laboratory of Wasserverband Peine located in Baddeckenstedt,
where samples ware brought for the experiment of COD, BOD5, NH4-N, NO3-N, TN
and TP. In the Lab, wastewater sample was tested by the HACH LANGE cuvettes
test method and this method being much easier, saves space, time and high
efficiency of achieving the reliable data. The procedure of measurement of COD,
NH4-N, NO3-N, TN and TP was same as Gadenstedt treatment plant and detail
described in section 8.1.5.3 of this chapter. Only measurement procedure was
different in the case of BOD5 than HACH LANGE cuvettes method. The
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measurement method proceed in the laboratory is also known as „‟ operational
analytical method‟‟ and is an alternative to reference DIN method. The sample after
collecting in Berel treatment plants is returned into the laboratory within the 1 hour
and sample analyses are conducted.
Fig 8.31: left: Mr. Marko Lux (Lab technician) using the Homogenizer to homogenize the sample and right: Sample of wastewater in the Lab for the analysis. (Wasserverband Peine Laboratory at Baddeckenstedt)
Biochemical Oxygen Demand (BOD5)
BOD is measured by using OxiTop® BOD
Respirometer Systems. This method is based on a
pressure measurement in a closed system where
microorganisms in the sample consume the oxygen
and form CO2. This is absorbed by NaOH, creating a
vacuum which can be read directly as a measured
value in mg/l BOD. The sample volume being tested
regulates the amount of oxygen available for a
complete the respirometer system's BOD
measurement. BOD measurement ranges of up to 4,000 mg/l can be measured with
the respirometer system using different sample volumes. The OxiTop® BOD
respirometer systems have two different heads; one is green used for inflow and
yellow for outflow. The influent sample of 164 ml is taken in green head bottle and
yellow head bottle is filled with 432 ml effluent sample after then mixed with 2 tablets
NaOH. These samples are kept inside the heating box at room temperature for 5
Fig 8.32: OxiTop Respirometer for
BOD measurement in Laboratory
93 Chapter 8: Case Study of Project Area
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days. However, every day one value of effluent and influent are observed and
recorded and continue up to 5 days. The final value after 5 days is measured as
BOD5 values, but there is some constant multiple factor to obtain the exact value of
BOD5 in the case of influent and generally the measured value is multiplied by 10.
Respirometer systems further measured BOD values that can be read at all times
after the period of 5 days, which permits the tracking of check values or
measurements over longer periods.
Chemical oxygen demand (COD) For the COD analysis, Hach - Lange method was followed and selected the LCK -
514 cuvettes test for the inflow wastewater sample considering the COD
concentration range 100 – 2000 mg/l O2 and LCK – 414 cuvette test for the effluent
water with low COD concentration ranging 5 - 60 mg/l. Four cuvettes is taken and
filled with 2 ml sample water, initially homogenized with the help of homogenizer and
screened with filter paper. Detail measurement process of COD is followed as
instruction given and described detail in section 8.1.5.3.
Ammonium nitrogen (NH4-N) In the laboratory, for the measurement of NH4-N, LCK 303 and LCK 305 cuvette test
method is used for the measurement of influent and effluent of wastewater sample of
Berel. Detail processes are same as Gadenstedt sample measurement, which is
described in detail in chapter 8.1.5.3
Nitrate-Nitrogen (NO3 -
N) and Nitrite-Nitrogen (NO2-N) In the laboratory, nitrate nitrogen (NO3-N) is analyzed very quickly by LCK -340 and
LCK- 339 cuvettes test method. In LCK -340 cuvettes test is conducted considering
the concentration of NO3-N high in influent sample in the range of 5- 35 mg/l and LCK
-339 cuvettes test for the NO3-N concentration low in effluent of sample within the
range of 0.23 – 13.5 mg/l. Nitrite is tested in the laboratory by the LCK -342 cuvettes
test method. Considering nitrite nitrogen concentration in the wastewater sample
should be low as within the range of 0.6 – 6.0 mg/l.
94 Chapter 8: Case Study of Project Area
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Total phosphorus (TP) Total phosphorus was analyzed by LCK - 350 and LCK - 348 cuvettes test method.
Influent and effluent of waste sample taken from settling pond was analyzed by LCK
– 350 cuvette considering the phosphorus concentration on the range of 2-20 mg/l
and effluent from constructed wetland and final polishing pond was analyzed by LCK-
348 cuvette test with low range of phosphorus (0.5-5.0 mg/l).
95 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
9 Results and discussion
The mean value for sampling data are taken for the analysis and other parameters
that are being studied covers the six main wastewater sampling i.e. COD, BOD, NH4-
N,TN,TP and pH. Other analysis including nitrate, nitrite and temperature are
included in this study.
9.1 Chemical Oxygen Demand (COD) of Gadenstedt and Berel WWTP
Fig 9.1: COD influent and effluent values at Gadenstedt WWTP
Chemical Oxygen Demand (COD) is a widely known parameter used to measure the
amount of oxygen required that can chemically oxidize organic matter as well as
inorganic substances present in the wastewater. COD values are much larger than
BOD values due to presence of humic materials in wastewater. For untreated
domestic wastewaters, COD concentration is found on the range of 250 - 1000 mg/l
(Metcalf and Eddy, 1991).
The above graph shows that concentration of COD in wastewater varies from 114
mg/l in November to 460 mg/l in July. The average value of influent of total 52
samples is 257 mg/l. This shows that volumetric loading of COD on the trickling filter
is 0.23 kg/m3.d. The effluent COD concentration is mostly below than 50 mg/l except
in the month of February and July. However, the average value of COD is 38.23 mg/l
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
COD Influent 293.0 204.5 134.0 264.0 306.0 281.5 460.0 292.0 155.0 214.0 114.0 214.0
COD Effluent of TF 42.0 57.0 37.0 31.7 43.3 34.8 58.4 40.5 24.8 27.6 25.3 22.7
COD Effluent of CWs 17.0 21.0 15.0 12.9 17.7 14.6 19.5 18.3 16.1 15.0 15.0 15.0
0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
400.0
450.0
500.0
mg
/ l
COD influent and effluent ,Gadenstedt
365
588
455511 486 468 477
558 568 569 555 531
Inflow Discharge (Q) - m3/d
96 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
that effluent from the trickling filter. The surface loading rate on the CWs is varied
from 50 l/m2.d to 78 l/m2.d and found average organic loading of 2.68 g/m2.d. Final
COD effluent of CWs is on the range of 14-21 mg/l. (See in Appendix -1 more detail
COD values)
Fig 9.2: COD reduction efficiency of CWs and TF at Gadenstedt WWTP
From the graph 9.2, COD is reduced by the trickling and constructed wetlands on the
range of 72-89 % and 4 -18 % respectively. And overall efficiency plant is found 93 %
where trickling filter contributes up to 84 % and CWs up to 9 %. The graph clearly
shows that effluent level of COD from trickling filter and constructed wetlands are
mostly below the legal limit of 110 mg/l mentioned by German Federal Government
Law and 90 mg/l by specific limit of Lahstedt wastewater treatment plant.
Similarly, in the case of Berel wastewater treatment plant, COD concentration in
wastewater varies on the range of 223 – 820 mg/l. Firstly, wastewater is treated by
settling pond, which helps to reduce the COD by 20 -72 % except August. Effluent
values are found on the range of 72.9 – 350.5 mg/l. Similarly, effluent waster from
settling pond is pumped and dosed over vertically flow CWs at the surface loading
rate of 59 l/m2.d under intermittent system. The water is then drained vertically under
gravity and voids in the filter media are refilled with air from the atmosphere. This
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
% reduced by CWs 9% 18% 16% 7% 8% 7% 8% 8% 6% 6% 9% 4%
% reduced by TF 86% 72% 72% 88% 86% 88% 87% 86% 84% 87% 78% 89%
86%72% 72%
88% 86% 88% 87% 86% 84% 87%78%
89%
9%18% 16%
7% 8% 7% 8% 8%6% 6%
9% 4%
0%
20%
40%
60%
80%
100%
120%
COD reduction in %, Gadenstedt
97 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
mechanism helps to provide sufficient oxygen to oxidize the organic and inorganic
materials present in wastewater.
Fig 9.3: COD influent and effluent values and reduction efficiency at Berel WWTP
COD concentration remains on the range of 18.3- 75.9 mg/l on the effluent of CWs
and overall reduction efficiency is achieved by 44 %.
The surprising results show that final effluent from maturation pond contains more
COD value than effluent value of CWs. Only in the month of January, February and
August COD values are reduced with very low percentage (1-2%) and remaining
months of the year, COD values are increased by 2 – 14 %. COD increased in the
polishing pond is the main cause of algae lifecycle phenomenon.
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
COD Influent 469.3 820.3 407.5 716.8 496.0 449.0 547.8 336.5 223.0 318.3 224.7 317.8
COD Effluent of SP 297.8 350.5 221.7 231.5 334.0 179.7 154.8 324.7 72.9 255.7 127.0 158.3
COD Effluent of CWs(1+2) 75.9 68.6 34.5 28.0 28.5 30.8 44.5 44.8 37.6 19.1 18.3 30.8
COD Effluent of PP 67.7 59.1 62.2 68.8 43.4 52.8 78.5 44.1 43.1 36.5 42.1 74.8
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
900.0m
g /l
COD influent and effluent , Berel
37%57%
46%
68%
33%
60%72%
4%
67%
20%
43% 50%
47%
34%46%
28%
62%
33%20%
83%
16%
74%
48% 40%
2%1%
-7% -6% -3% -5% -6%
0%
-2% -5% -11% -14%
-20%
0%
20%
40%
60%
80%
100%
120%
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
Pe
rce
nt
Months
COD reduction at Berel WWTP
% reduction by SP % reduction by CWs(1+2) % reduction by MP
132.0 125.5
190.0
147.0 150.0
94.564.0
87.0
137.5 123.0
219.5 231.0
Inflow Discharge (Q) - m3/d
98 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
However, finally COD effluent from MP and CWs are below the legal limit of 150 mg /l
mentioned by German Federal Government law and 100 mg /l by specific limit of
Berel WWTP.
9.2 Biochemical oxygen demand (BOD5) of Gadenstedt and Berel WWTP
Biochemical oxygen demand (BOD) is an approximate measure of the amount of
biochemically degradable organic matter present in a water sample. It is defined by
the amount of oxygen required for the aerobic microorganisms present in the sample
to oxidize the organic matter to a stable inorganic form. The method is subject to
various complicating factors such as the oxygen demand resulting from respiration of
algae in the sample and the possible oxidation of ammonia (if nitrifying bacteria are
also present). Other parameters like pH- value, temperature, or presence of toxic
substances in a sample may affect microbial activity leading to a reduction in the
measured BOD. Therefore, interpretation of BOD results and their implications has
done with great care.
Fig 9.4: BOD5 influent and effluent values at Gadenstedt WWTP
The above graph shows the analysis of BOD5, sample measurement from
Gadenstedt treatment plants. The BOD5 concentration in the wastewater is varied
with a maximum 182 mg/l in July and minimum 56 mg/l in November. The average
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
BOD5 mg/l Influent 112.0 103.3 70.0 110.8 159.8 139.3 182.2 109.3 94.8 95.5 56.0 76.2
BOD5 mg/l Effluent of TF 10.25 16.8 14.0 10.3 9.3 5.8 10.4 4.3 4.8 4.3 5.5 4.6
BOD5 mg/l Effluent of CWs 4.00 7.3 6.2 4.0 5.3 3.8 2.4 3.3 5.4 4.0 4.0 4.0
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
180.0
200.0
mg
/ l
BOD5 inflow and outflow ,Gadenstedt
n = 52
BOD5 inflow = 109 mg/l (avg.)
99 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
value of BOD5 in influent lies 109 mg/l and these values are much higher than the
recommended by German Federal Government. The effluent BOD5 of trickling filter is
found on the range of 4.3 – 16.8 mg/l with average value 8.35 mg/l that shows the
reduction efficiency of BOD in trickling filter on the range of 80-96%, when comparing
the influent and effluent of trickling filter. Similarly, BOD5 concentration in the final
effluent from the constructed wetlands is found 2.4 – 7.3 mg/l (with average 4.46
mg/l) and reduction efficiency of CWs varies also on the range of 1 – 11 %, when
comparing the TF and CWs with respect to influent concentration.
Fig 9.5: BOD5 reduction in percent by TF and CWs
Above fig 9.4 clearly shows that effluent value of BOD5 from trickling filter and CWs
are mostly below the legal limit of 25 mg /l given by German Federal law and
Gadenstedt WWTP. But only on the month of January, BOD5 level is higher than
legal limit.
The major cause of BOD removable depends upon the trickling filter operation and
development of high growth of microorganisms. During the operation, the wastewater
trickles over the surface of media and develop the visible shiny slime. The organic
material present in the wastewater is absorbed and metabolized by the micro-
organisms in the presence of oxygen under the aerobic condition. They produce
more organisms, carbon dioxide, sulfates, nitrates and other stable byproducts. The
oxygen supply is seemed to be enough to decompose the organic matter and
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
% reduced by CWs 6% 9% 11% 6% 3% 1% 4% 1% -1% 0% 3% 1%
% reduced by TF 91% 84% 80% 91% 94% 96% 94% 96% 95% 96% 90% 94%
91% 84% 80%91% 94% 96% 94% 96% 95% 96% 90% 94%
6% 9% 11%6% 3% 1% 4% 1%
-1%
0% 3% 1%
-20%
0%
20%
40%
60%
80%
100%
120%BOD5 reduction in % ,Gadenstedt
100 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
nitrification. This is one of the evidence of the old trickling filter operating properly
with high efficiency.
In the case of constructed wetlands, they are designed for vertically flow and
intermittent hydraulics loading system. Hydraulic loading rate is found 70 l/m2.d and
organic (BOD5) loading is found 0.59 g/ m2.d. The water is drained by gravity and
voids are refilled with air from the atmosphere considering porosity 30-40 %. This
mechanism helps to provide sufficient oxygen for aerobic process. The substrate
used in constructed wetlands whose hydraulic conductivity was designed 10-3 m/s,
which permit water to flow through the filter media without clogging. This shows that
CWs are in good function whereas CWs is treating as the tertiary treatment plant only
for polishing purpose. BOD reduction in constructed wetlands is assumed that
oxygen is transferred by plant through the roots into rhizomes and aerobic condition
exits which help to decompose the organic matter by micro-organism. There are
different views found in the literature on how much excess oxygen that is available for
biological activity in the root zone of constructed wetlands.
The flux of oxygen transferred into the rooting system has been tentatively quoted to
be 4-5 gO2/m2d (Armstrong et al., 1988). The oxygen transferred into the root zone
by Phragmites australis was 2.08 g /m2.d, but root and rhizomes consumed the
oxygen for respiration was measured 2.06 g /m2.d, which show the perfectly balance
oxygen influx through the culms leaving only 0.02 g/m2.d to be released to the
surrounding matrix and these values are far lower than those quoted (30-150 g/m2d)
for vertical flow system (Brix et al., 1990). It is also much lower than the oxygen
demand of 8 – 10 g O2 /m2d for a bed designed at 5 m2/ pe for BOD removal only
(Cooper et al., 1996). With reference of literature, it is very difficulties to find out such
kind scientific measurement in the study area, but it is concluded that vegetated
plants are more important for better hydraulic conductivity rather than supply of
oxygen.
In the case of Berel, the data taken are not consistency in the case of BOD
measurement. The effluent of BOD5 from settling pond was measured only in the
February and March with the value 200 mg/l and 185 mg/l respectively. The reduction
percentages were 35 % and 12 %. The effluent values of BOD in CWs are an
average value of 22.0, 10.0 and 9.0 mg/l respectively (average 13.67 mg/l) during
101 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
January, February and March, which shows removals efficiency of 80 %. The ability
to reduce BOD shows that the microorganisms in constructed wetlands have been
developed well and the wetland has a design that gives sufficient time and internal
surface for degradation of organic matter to occur. These values are below the legal
limit of 40 mg /l stated by German Federal law and 25 mg /l stated by Berel WWTP
for the small treatment plant up to one thousands inhabitants.
Fig 9.6: BOD influent and effluent measured values of wastewater in Berel.
9.3 Ammonium nitrogen (NH4- N) of Gadenstedt and Berel WWTP
The most important inorganic forms of nitrogen in wetlands treating municipal or
domestic wastewater are ammonia (NH4+), nitrate (NO3-), nitrite (NO2-) and nitrous
oxide (N2O) and dissolved element nitrogen or nitrogen gas (N2) (Kadlec and
Wallace, 2009). Ammonia exists in water solution as either as un-ionized ammonia
(NH3) or ionized ammonia (NH4+, ammonium ion), depending upon water temperature
and pH.
At the time of the study, the plant was operating at a design flow of 512.83 m3 per
day with a hydraulic loading rate of NH4-N at the average of 0.017 kg /m3/d. Above
figure shows that the average concentration values of NH4-N in the wastewater is
more than 10 mg/l besides March (8 mg/l) and November (9.7 mg/l) .In the summer
these values can be found maximum on the range of 20-34.3 mg/l and in the winter
values varies from 16-18.3 mg/l respectively. (More detail can be seen in Appendix II)
Jan Feb Mar Apr May June Aug Sep Nov
BOD5 Influent 297.50 310.00 210.00 245.00 147.50 280.00 260.00 158.00 113.33
BOD5 Effluent of SP 200.00 185.00
BOD5 Effluent of CWs(1+2) 22.00 10.00 9.00
BOD5 Effluent of PP 15.33 13.25 14.00 18.25 5.75 22.37 4.75 7.80 12.33
0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
mg
/ l
BOD5 influent and effluent , Berel
102 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Fig 9.7: NH4-N influent and effluent values at Gadenstedt WWTP
.Average monthly effluent NH4-N values from TF during colder temperature periods
varied from 1 to 3.3 mg/L. Similarly in summer average monthly value of NH4-N is on
the range of 0.2 mg/l to 2.6 mg/l. Temperatures in winter is ranged between 5°C and
7°C, while the summer water and air temperatures ranged between 14° -18°C and
23-34°C respectively. (See Appendix IV of air and water temperature). Efficiency of
trickling filter for NH4-N removal varies between 80 to 99 % (average 93%).
In the case of Constructed wetlands, NH4-N surface loading is very low as 0.1 g/m2.d.
So NH4-N is reduced by CWs only in four months like January ,February ,May and
July by 10%, 5%, 14%, 6% respectively, otherwise the values are similar to effluent
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
NH4-N Influent 16.4 18.3 8.0 16.5 15.5 20.1 34.3 26.0 14.1 14.0 9.7 10.9
NH4-N Effluent of TF 3.3 2.7 0.2 0.3 2.3 0.3 2.6 0.6 0.2 0.2 1.0 1.0
NH4-N Effluent of CWs 1.7 1.8 0.2 0.2 0.2 0.2 0.4 0.4 0.3 0.2 1.0 1.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
mg
/ l
NH4-N influent and effluent , Gadenstedt
Table 9.1: NH4-N reduction in percentage by TF and CWs
Month % reduction by TF % reduction by CWs
Overall efficiency
Jan 80% 10% 90%
Feb 85% 5% 90%
Mar 98% 0% 98%
Apr 98% 0% 99%
May 85% 14% 99%
June 98% 0% 99%
July 92% 6% 99%
Aug 98% 1% 99%
Sep 99% -1% 98%
Oct 99% 0% 99%
Nov 90% 0% 90%
Dec 91% 0% 91%
103 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
from trickling filter. However, finally NH4-N effluents from CWs are below the legal
limit of 10 mg /l mentioned by Gadenstedt WWTP. Overall efficiency of NH4-N
reduction is found by 96%.
In Berel, NH4-N concentration in the wastewater varies from lowest 34.4 mg/l to
maximum 61mg/l as shown in fig 9.8. After retention in settling pond, effluent values
of NH4-N are found on the range of 17- 41.9 mg/l and discharge into the CWs at the
surface loading rate of 59 l/m2.d and organic loading 1.8 g/m2.d.
Fig 9.8: NH4-N influent and effluent values at Berel WWTP
Concentration of NH4-N effluent from CWs is lower than 10mg/l from April to
December. The effluent values of NH4-N are more than 10 mg/l in three months like
January, February, and March. From the fig 9.9, the efficiency of SP and CWs for
NH4-N reduction varies within 20 - 56 % (with average 38 %) and 22 -70 % (with
average 48%). Similarly, final effluent from maturation pond shows the very low
efficiency of NH4-N reduction only in four months like March. April, May and July on
the range of 1-10% .In the other hand, concentration of NH4-N increased in remaining
months varies from 4 % to 26 % beside above mentioned four months. (More detail
can be seen in Appendix II)
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
NH4+ Influent 51.6 61.0 50.0 40.7 42.1 48.7 54.8 58.6 42.7 52.4 40.6 34.4
NH4+ Effluent of SP 41.5 41.4 26.9 20.3 27.6 32.0 39.9 41.9 24.5 25.2 17.9 23.4
NH4+ Effluent of CWs(1+2) 18.8 26.3 15.7 6.8 1.8 1.5 1.6 1.3 1.0 0.4 0.4 6.9
NH4+ Effluent of PP 26.9 28.6 12.5 3.0 0.7 4.1 1.1 1.5 4.2 7.3 10.7 12.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
mg
/l
NH4 - N influent and effluent ,Berel
104 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Fig 9.9. NH4-N reduction efficiency of Berel WWTP
From the above result analysis of Gadenstedt and Berel wastewater treatment plants,
it can be concluded that ammonium nitrogen is reduced by converting into nitrate
through nitrification process. Biological nitrification takes places in the trickling filter
and constructed wetlands converting ammonia in wastewater to nitrate using aerobic
autotrophic bacteria in the treatment process. Nitrification is actually a two-step
process for removing ammonia from wastewater using two different types of
autotrophic bacteria. In the first step ammonia is oxidize to nitrite by bacteria in the
genus Nitrosomonas under nitritation and then oxidize nitrite to nitrate by bacteria in
the genus Nitrobacter under nitrification (Kadlec and Wallace, 2009). These bacteria
known as “nitrifiers” are strict “aerobes,” meaning there must have free dissolved
oxygen to perform their work. Biological nitrification systems are designed in the
trickling filter and constructed wetlands to completely convert all ammonia to nitrate.
Oxidized nitrogen forms (e.g., nitrite and nitrate) do not bind to solid substrates, but
ammonia is capable of sorption to both organic and inorganic substrates. Because of
the positive charge on the ammonium ion, it is subjected to cation exchange .Ionized
ammonia may therefore be removed from water through exchange with detritus and
inorganic sediments in constructed wetlands. But it is not analyzed how much
ammonia is absorbed in the soil substrate of constructed wetlands. Based on the
-40%
-20%
0%
20%
40%
60%
80%
100%
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec% reduction by MP -16% -4% 6% 10% 3% -5% 1% 0% -7% -13% -26% -16%
% reduction by CWs 44% 25% 22% 33% 61% 63% 70% 69% 55% 47% 43% 48%
% reduction by SP 20% 32% 46% 50% 34% 34% 27% 28% 43% 52% 56% 32%
20%32%
46% 50%34% 34% 27% 28%
43%52% 56%
32%
44% 25%
22%33% 61% 63% 70% 69%
55%47% 43%
48%
-16%-4%
6%
10%3%
-5%
1%
0% -7% -13%-26%
-16%
NH4 - N reduction in % ,Berel
105 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
stoichiometric relationship, Kadlec and Wallace (2009) pointed out theoretically that
total oxygen required 4.57 g per gram of NH3-N oxidized in which 3.43g O2 per gram
of NH3-N oxidized by the first nitritation reaction and 1.14g O2 by the second
nitrification reaction. Similarly, Cooper and Job (1996) explained about approximately
4.3 mg O2 per mg of NH4-N is required to oxidize into nitrate nitrogen and nitrification
occurs only under aerobic conditions at dissolved oxygen levels of 1.0 mg/L or more.
This result shows that oxygen is available in sufficient quantity for microbial activity to
convert ammonium nitrogen into nitrate in the trickling filter and constructed wetlands.
In the case of constructed wetlands, influent wastewater flow vertical through the filter
media and feeding intermittent system, so maximum oxygen entered the bed from
atmosphere via pores and root. But at Gadenstedt, there is very low organic loading
rate in influent of CWs, so there is low efficiency for reduction of ammonium nitrogen.
The efficiency of treatment plant for ammonium nitrogen reduction in Gadenstedt and
Berel is found 86% and 81% respectively. The discharge of ammonium nitrogen from
wastewater treatment plants has a very less amount and it is not challenging for
aquatic life.
9.4 Total nitrogen (TN) analysis of Gadenstedt and Berel WWTP
Total Nitrogen (TN) is the sum of nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N),
ammonia-nitrogen (NH3-N) and organically bonded nitrogen. Total Nitrogen (TN)
should not be confused with TKN (Total Kjeldahl Nitrogen) which is the sum of
ammonia-nitrogen plus organically bound nitrogen but does not include nitrate-
nitrogen or nitrite-nitrogen. TN is sometimes regulated as an effluent parameter for
municipal and industrial wastewater treatment plants, but it is more common for limits
to be placed on an individual nitrogen form, such as ammonia. Treatment plants that
have a TN limit will usually need to nitrify and denitrify in order to achieve the TN
limit.
This graphs shows that total nitrogen concentrations in wastewater varies from
minimum 29.4 mg/l to maximum 47 mg/l with an average value of 39.6 mg/l. The
effluent TN from trickling filter varies from 12.8 – 15.4 mg/l in summer and on the
range of 16.5 – 18.6 mg/l in winter.
106 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Fig 9.10: Total nitrogen (TN) influent and effluent values at Gadenstedt WWTP
Likewise, lowest concentrations of TN in the effluent of CWs are found June, July and
August with an average value of 2.1 mg/l, 3.6 mg/l and 1.3 mg/l respectively. TN
effluent from constructed wetland is found 7.22 mg/l (average), this value is 73% less
than the legal limiting limit of 27 mg/l mentioned by Gadenstedt WWTP and overall
efficiency of TN reduction is found 81 % (trickling filter - 58% and CWs - 23 %).
Influent
mg/l
Effluent of TF
mg/l
Effluent of CWs
mg/l
NH4-N 16,97 1,20 0,61
NO3-N - 14,75 6,61
NO2-N - 0,09 0,07
Nges 39,66 16,07 7,22
N org 16.89 - -
Table 9.2: Annual average value of nitrogen concentration at Gadenstedt WWTP (year 2010, sample n=52)
Nitrogen contains in different form which polluted water is originally present in the
form of organic nitrogen and ammonia. In the table 9.2, organic nitrogen and
ammonia concentration in waste water are 43% and 43 % respectively. From the
above table shows wastewater with TN (39.6 mg/l) in which 43 % concentration as
NH4 –N and 43 % organic nitrogen, entered into the trickling filter, it goes under
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
TN Influent 44.5 38.4 37.7 43.5 38.6 44.3 47.0 39.6 34.6 29.4 35.9 42.0
TN Effluent of TF 17.7 18.6 16.5 17.3 20.9 15.4 11.5 12.8 12.5 18.7 16.0 16.5
TN Effluent of CWs 12.6 12.1 9.7 8.3 5.8 2.1 3.6 1.3 4.2 7.9 8.0 12.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0m
g /
lTotal Nitrogen influent and effluent ,Gadenstedt
107 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
biochemical process which converts organic ammonia nitrogen into ammonia and
further oxidized first into nitrite, then into nitrate. Then effluent of NH4 –N, NO3-N and
NO2-N contains 1.2 mg/l, 14.75 mg/l and 0.09 mg/l respectively. This results show
nitrite and ammonium nitrogen are at minimum concentration (at or near zero) and
nitrate is at a maximum value, the wastewater has been fully nitrified. A fully nitrified
wastewater will have little or no organic nitrogen being utilized as a nutrient by
microorganisms in the treatment process (www.asaanalytics.com/total-
nitrogen.php)
Fig 9.11: Total Nitrogen influent and effluent values of Berel WWTP
In the case of Berel, effluent data of NO3-N, NO2-N and TN was measured in the
constructed wetlands and polishing pond to analysis the efficiency of treatment
process. Data analysis about the ammonium nitrogen was already discussed in
previous section 9.3 of this chapter.
Table 9.3: Monthly average effluent data of different nitrogen form measured in constructed wetlands and polishing pond at Berel WWTP (data - 2010, n = 46 sample)
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
TN Effluent of CWs 24.7 31.1 44.4 46.4 35.1 29.9 45.9 45.6 32.4 21.1 23.8 13.2
TN Effluent of PP 28.6 29.5 20.8 14.7 5.9 4.7 1.4 4.2 9.8 11.9 14.1 13.4
0.0
10.0
20.0
30.0
40.0
50.0
mg
/ l
Total nitrogen influent and effluent ,Berel
CWs PP
Month NH4-N NO3-N NO2-N TN NH4-N NO3-N NO2-N TN
Jan 18,81 5,74 0,19 24,74 26,9 1,7 0,1 28,6
Feb 26,26 4,65 0,23 31,14 28,6 0,8 0,1 29,5
Mar 15,67 29,44 0,90 44,38 12,5 6,4 1,3 20,8
Apr 6,85 39,16 0,42 46,42 3,0 11,0 0,8 14,7
May 1,80 32,90 0,43 35,12 0,7 5,0 0,2 5,9
June 1,50 28,28 0,11 29,89 4,1 0,4 0,2 4,7
July 1,63 44,23 0,07 45,93 1,1 0,3 0,0 1,4
Aug 1,27 44,23 0,07 45,57 1,5 2,4 0,3 4,2
Sep 0,97 31,35 0,07 32,39 4,2 6,9 0,6 9,8
Oct 0,41 25,97 0,05 21,13 7,3 5,7 1,0 11,9
Nov 0,35 23,38 0,06 23,79 10,7 4,9 0,5 14,1
Dec 6,95 6,17 0,08 13,20 12,5 0,8 0,2 13,4
108 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
From the above table 9.3, effluent value of NO3-N is low in winter seasons varies
from 4.66 – 6.95 mg/l, when the water temperature was 5-7°C and maximum
effluents during the summer in June and July with the average value of 44.23 mg/l
,when the water temperature is found 14 -18°C (see the temp fig 9.17). The
nitrification process is temperature dependent so nitrification is occurred in CWs
during the summer by Nitrosomonas and Nitrobacter converting ammonia and
ammonium to nitrite and nitrite to nitrate. The reaction is generally coupled and
proceeds rapidly to the nitrate form, which means nitrite produced by Nitrosomonas is
instantly oxidized by Nitrobacter to nitrate and therefore, the concentration of NO2-N
is very less or near to zero (Schneider and Fresenius, et. al 1989).
Similarly, the effluent values of NH4-N from polishing pond are high in winter and
minimum in summer. Nitrate values are on the range of 0.3-11.0 mg/l shows the
denitrification process occurred in the reduced environment of the water column,
where anoxic conditions prevailed. This may be due to the thicker sediment layer- as
dead algae settled in the bottom as sediments that contained more denitrifying
organisms. Nitrates reduce to nitrites, which in turn easily combine to form
substances dangerous to man. Total nitrogen concentration fluctuation is highly
depended upon the nitrification and denitrification process in the treatment system.
TN effluent finally into the receiving water course is 1.4 – 4.7 mg/l in summer and
maximum values in winter varies 13.4 -29.5 mg/l, however, these values are below
the legal limit of 40 mg/l authorized by Berel WWTP.
The WHO recommended as „‟International Standards„‟ for the maximum limit for
nitrate concentration in the drinking water is 50 mg/L, which is equivalent to 11.3 mg/l
as NO3-N (Chilton, 1996). Similarly, Mohaupt et al. (1996) reported that nitrate (NO3-
) concentration in surface water samples in Germany is not higher than 25 mg/l,
which is half the drinking water limit. Concentration of NO3- as low as 10 mg/l are
deem unacceptable for the baby food, which causes methemoglobinemia problem
and nitrite as low as ca. 10 to 20 mg/l are highly toxic for fish (Schneider and
Fresenius et al., 1989). In Europe, the maximum consented level of nitrates in
potable water is 50.0 mg/L (www.environ.ie), while in the USA the EPA has
established a guideline for the maximum level of nitrate nitrogen of 10 mg/L (NO-3-
N), which corresponds, to 45.0 mg/L of nitrates. Nitrogen removal on the other hand
is effected through sediment accumulation, adsorption of ammonium onto the organic
109 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
sediments (Howard-Williams, 1985), plant uptake and nitrification-denitrification
processes.
9.5 Phosphorus of Gadenstedt and Berel WWTP
Phosphorus appears in different form in wastewater as orthophosphate, dehydrated
orthophosphate (polyphosphate) and organically bound phosphorus, due to biological
oxidation results in the conversion of most of phosphorus to the orthophosphate
forms ( H2PO4-, HPO4
2-, PO43-)(Cooper el at., 1996). Microbes utilize phosphorus
during cell synthesis and energy transport. As a result, 10 to 30 percent of the
influent phosphorus is removed during traditional mechanical / biological treatment
(Metcalf and Eddy, 1991). Phosphorus is important nutrients for the plants growth
which are used in during the growing seasons.
Fig 9.12: phosphorus influent and effluent values of Gadenstedt WWTP
There is no legal limit specified by German federal Government about the
phosphorus concentration in wastewater before discharging to receiving water course
concerning to the small treatment plant for less than 5000 population. But only
specific legal limit of 5 mg/l phosphorus concentration in effluent water according to
Gadenstedt WWTP. In the fig 9.12, P concentration is found 7.3 mg/l in July and
August and 5.3 mg/l in January, which are higher than legal limit. After then the
remaining month‟s concentration is below the 5 mg/l. Effluent form trickling filter is
found on the range of 1.5 – 4.6 mg/l (average 2.6 mg/l), and final effluent of CWs is
varied from 1.2 mg/l to 2.6 mg/l (average 1.8 mg/l) respectively. P reduction efficiency
by TF and CWs are 37% and 17% respectively.
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
TP Influent 5.3 3.7 1.8 4.0 3.9 4.3 7.3 7.3 3.0 3.6 2.8 3.1
TP Effluent of TF 1.9 2.4 1.5 2.2 2.9 2.7 4.6 4.6 1.6 2.7 1.8 1.7
TP Effluent of CW 1.5 2.0 1.2 1.5 1.8 1.5 2.6 2.6 2.1 1.6 1.2 1.4
0.01.02.03.04.05.06.07.08.0
mg
/ l
phosphorus influent and effluent , Gadenstedt
110 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Fig 9.13: phosphorus influent and effluent values of Berel WWTP.
In the case of Berel, P inflow concentration was not as high as compare to limiting
values of 8 mg/l given by Berel WWTP and here only in three months, the
phosphorus values are more than limiting values in February, July and October as
12.76 mg/l, 10.18 mg/l and 11.45 mg/l respectively. Phosphorus effluent from settling
pond is average value of 6.27 mg/l, representing 22 % reduction and only the effluent
value varies by 52 % in August. In construction wetland, P is reduced highly by 74%,
58% and 102 % respectively in summer (June, July and August). In winter seasons,
CWs is also functioning properly to trap the phosphorus and reduced by 35 % and in
autumn by 27 % respectively. Final P removable efficiency of CWs is found 41%.
Fig 9.14: Phosphorus reduction efficiency of Berel WWTP
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
Pges Influent 8.39 12.76 7.70 8.11 8.57 7.57 10.18 6.80 5.65 11.45 6.51 5.58
Pges Effluent of SP 6.74 6.86 4.59 4.91 6.16 7.50 7.81 10.36 4.97 7.26 4.25 3.81
Pges Effluent of CWs(1+2) 2.77 3.01 5.18 2.36 1.77 1.94 1.94 3.38 3.56 2.61 3.20 2.31
Pges Effluent of MP 4.49 4.59 3.93 3.16 3.19 4.25 4.04 2.85 3.14 3.60 4.14 3.75
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
mg
/ l
Phosphorus influent and effluent ,Berel
-60%
-40%
-20%
0%
20%
40%
60%
80%
100%
120%
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
20%46% 40% 39% 28%
1%23%
-52%
12%37% 35% 32%
47%
30%
-8%
31% 51%
74%
58% 102%
25%
41%16% 27%
-20% -12%
16%
-10% -17%-31% -21%
8%
7%
-9% -14%-26%
phosphorus reduction in % ,Berel
Effluent of SP Effluent of CWs(1+2) Effluent of MP
111 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
It was found interesting by the data analysis in fig 9.14 that effluent value of
phosphorus from maturation pond increased in the month of summer like June and
July by 31% and 21% with comparison to constructed wetlands. Similarly in winter
concentration also varies from 12 % in February to 26 % in December. The study
shows that P concentration is increased by average value of 11% in comparison to P
effluent of CWs. However final P concentration on effluent is an average value of
3.76 mg/l, which is nearly 47 % less than the legal limiting values.
The possible mechanisms of phosphorus removal in vertical flow through beds
comprise plant uptake, assimilation by micro-organisms and physico-chemical
processes associated with the bed media. Most of the phosphorus in the soil column
is structural phosphorus, both organic and inorganic. Very small fraction is found in
pore water or as sorbed phosphorus. It is assumed that Phragmites (reed), are
planted in constructed wetlands of Gadenstedt and Berel, uptake phosphorus from
root zone as an important nutrients, which are used during the growing seasons.
Kadlec and Wallace et.al (2009) indicated that especially most plant roots are found
on the top soil layer at the depth of 0-10 cm, which helps to remove phosphorus with
high concentration from this zone by taking up during the cycle of growth.
Phosphorus sorption is heavily influenced by the amount of calcium carbonate,
aluminum oxides and iron oxides and organic matter present in the bed aggregate
(Vohla et al., 2008). But it is also notable that algae growth, death, decomposition in
pond and plant growth, death, decomposition, litter formation may increase in
phosphorus mass during the cold seasons.
Jin et al (2005) estimated that P sorption reactions are endothermic, colder water
temperatures will decrease the apparent sorption capacity of the bed aggregate. By
the study of Gadenstedt, sorption capacity decreased by 10% when the water
temperature was decreased from 18°C to 5°C. Similarly in the case of Berel, sorption
capacity decreased by 8 % after water temperature decreased from 19 °C to 3 °C.
Generally the amount of phosphorus that can be recovered through harvesting of
emergent wetland plants is about 5-10 g/m2 (Vymazal et al., 2005a). Maximum
nutrients by emergent macrophytes was found to be in the range of 200-1560 kg
N/ha and 40 -375 kg P/ha in Florida (Reddy and DeBusk, 1987). Phragmites (reed)
112 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
stored the phosphorus in tissue at the rate of 2-3 g P /kg and biomass growth varies
10 – 60 t/ha .yr (www.fao.org). Emergent macrophytes uptake nutrients depend upon
the climate, plant density, loading rate and culture system. It is better to harvest
above ground biomass once a year rather than frequently harvesting should improve
the overall nutrients efficiency. However, it is not found such kind of practice like
harvesting of emergent macrophytes from the constructed wetlands at Gadenstedt
and Berel WWTP.
9.6 pH value of Gadenstedt and Berel WWTP
The physical and chemical environment of a wetland affects all biological process.
Hydrogen ion concentration, measured as pH, influences many biochemical
transformations. It influences the partitioning of ionized and unionized forms of
carbonates and ammonia, and controls the solubility of gases solids, such as
ammonia and solids such as calcite. Hydrogen ions are active in cation exchange
processes with wetlands sedimentation and soils and determine the extent of metal
binding (Kadlec und Wallace, 2009).
Fig 9.15: pH value of influent and effluent of wastewater at Gadenstedt WWTP
In the above fig 9.15, the pH values of influent showed the fluctuation in every month
and found to be average values of 8.0, which showed the wastewater in basic (alkali)
nature. The pH effluent from trickling filter is found low in July and August with
average value 7.54 and maximum value in January, February, March and December
falls under the range of 7.96 to 7.99; however mean value of pH is 7.68. Wastewater
was treated through the trickling filter, water containing organic matter decomposed;
ammonium nitrogen in wastewater is oxidized first to nitrite nitrogen and then to
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
pH Influent 8.11 8.26 8.03 7.92 7.90 7.91 8.02 7.95 7.88 8.06 8.01 7.98
pH Effluent of TF 7.96 7.98 7.98 7.92 7.84 7.81 7.54 7.57 7.81 7.85 7.82 7.99
pH Effluent of CWs 7.54 7.70 7.54 7.58 7.41 7.18 7.17 7.12 7.16 7.14 7.30 7.48
6.406.606.807.007.207.407.607.808.008.208.40
pH influent and effluent value,Gadenstedt
113 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
nitrate through nitrification. The nitrification process produces acid and acid formation
lowers the pH value.
The pH value of final effluent water from constructed wetlands is found average value
of 7.36 during the analysis, whereas the pH value was lower in summer, autumn and
higher value in winter and spring respectively.
Fig 9.16: pH influent and effluent values of Berel WWTP
Similarly, in the case of Berel treatment plant, pH value of influent water in the first
settling pond was found more than 8.0, showing the alkalinity nature of wastewater.
pH effluent in settling pond is found on the range of 7.24 to 7.57 except October and
November before entering to constructed wetlands. After the oxidation of organic
matter and ammonium-nitrogen in the VF constructed wetlands during the
intermittent hydraulic loading system; aerobic reaction occurred and released the
carbon dioxide forming the carbonic acid, resulting the pH value reduced having
average value 6.7. Final pH effluent from polishing pond is found mean value of 7.68,
the main cause of algal activity. In the pond during the photosynthesis process algae
consumed the CO2 (Carbon Dioxide) after decomposed and leaving an excess of
hydroxyl ions. The major source of carbon dioxide for algae depends upon the
carbonate and bicarbonate ions reaction. As a result, the pH of the water is increased
up to 7.68 (average value) in polishing pond. The potential of increasing the pH of
wastewater to high levels by CO2 stripping through air, N2, O2 and a gas mixture
(95% N2+ 5% CO2) (Cohen and Kirchmann, 2004).
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
Influent 8.48 8.57 8.25 8.31 8.40 8.25 8.48 8.39 8.11 8.49 8.29 7.95
Effluent of SP 7.52 7.34 7.54 7.55 7.57 7.24 7.50 7.57 7.34 8.03 7.63 7.42
Effluent of CWs(1+2) 7.10 7.14 6.51 6.62 6.59 6.57 6.43 6.41 6.53 6.59 6.85 7.01
Effluent of PP 7.68 7.65 7.67 7.98 7.70 7.67 8.05 7.69 7.40 7.54 7.65 7.45
0.00
2.00
4.00
6.00
8.00
10.00 pH influent and effluent ,Berel
114 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
From the data analysis the main factor which affects the pH is the amount of plant
growth and organic material within a body of water. When this material decomposes
carbon dioxide is released. The carbon dioxide combines with water to form carbonic
acid. Although this is a weak acid, large amounts of it will lower the pH. The effluent
value of pH from trickling filter and constructed wetlands is basic nature, whose value
only little bit more than neutral water. pH is not changed drastically and cannot be
consider the synergy effect on the water. pH play a vital role for healthy aquatic
system, can function only within a limited pH range. As a consequence, surface
water discharge permits frequently require 6.5< PH <9.0. Wetland water chemistry
and biology are likewise affected by pH. Many treatment bacteria are not able to exist
outside the range 4.0< pH <9.5 (Metcalf and Eddy Inc., 1991). Denitrifies operate
best in the range 6.5 <pH <7.5 and nitrifies prefer pH =7.2 and higher.
This is one of the suitable environments for wetlands water chemistry for nitrifying
bacteria and microbiological degradation process. The Phragmites australis used in
constructed wetlands can withstand within the pH value of 4.8 to 8.2 (Duke, 1978,
1979). There is no harmful effect on the growth and survivable of Common Reed in
the constructed wetlands. The height of common reed is found to be 2-3 m in the real
field Gadenstedt and Berel. Due to very close value to neutral water, the effluent
water from constructed wetlands and polishing pond did not affect on the quality of
water in receiving river and seemed no danger to aquatic life present in the river.
9.7 Temperature
The water temperature in treatment wetlands is important for several reasons such
as: (1) Temperature modifies the rate of several key biological processes, (2)
Temperature is sometimes a regulated water quality parameter, (3) Water
temperature is a prime determined of evaporative water loss, (4) Cold–climate
wetlands systems have to remain functional in subfreezing condition (Kadlec and
Wallace et al., 2009).
Treatment wetlands are solar powered ecosystems, resulting in annual cyclic
temperatures, where an energy balance is dominated by radiation, heat transfer, heat
gains or losses, heat conduction and convection among the ground, the atmosphere
and the wastewater (Reed et al., 1995). Wetland energy flows are the proper
115 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
framework to interpret and predict not only evaporative process, but also wetlands
water temperatures (Kadlec and Wallace et al., 2009).
Fig 9.17: Annual pattern of water and air temperature at Gadenstedt WWTP
From the temperature figure of Gadenstedt and Berel, it is clearly showed that the
annual cycle of wetland water temperature as well as air temperature follows a
sinusoidal pattern, with a summer maximum and a winter minimum. The air
temperature in winter are varies from -4 °C to 0 °C, whereas water temperature
remains 5 - 7 °C. Similarly air temperature was maximum in summer varies from 23
to 34°C and water temperature remains 14 to 18 °C respectively. This is due to the
convection and diffusion method of water surface and transfer heat from air to the
wetland. From the correlation graphs, water temperature is dependent on air
temperature and around the less than 50 % heat is transferred into the wetlands (Tw
= 0.44 Ta, R2 = 0.74).
Evapotranspiration (ET) is the main causes of water losses to the atmosphere
through the water surface, media used and emergent vegetation in constructed
wetlands. But the presence of vegetation which helps to retard evaporation, main
reasons is shading of the surface, increased humidity near the surface and reduction
of the wind velocity at the surface. Another important effects of plants is to provides
insulation that helps protecting the soil from freezing during winter, but on the other
hand, it keeps the soil the soil cooler during the spring (Vymazal et al. 1998). Abtew
(1996) operated vegetated lysimeters for two years in marshes with three vegetation
types: 1) Typha domingensis, 2) a mixture including Pontederia cordata, Saittaria
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
Air Temp Min -4 0 4 7 9 14 18 15 11 8 4 -4
Air Temp Max 0 5 10 16 18 29 34 23 18 14 9 0
Water Temp average 6 5 7 10 11 14 18 17 15 13 14 7
-10-505
10152025303540
°C
Air and Water temperature ,Gadenstedt
116 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
latifolia and Panicum hemitomon, and 3) submerged aquatic Najas guadalupensis
and Ceratophyllum demersum. The annual average water losses (ETp) were 3.6, 3.5,
3.7 mm/d respectively.
Fig 9.18: Relationship between annual average water and air temperature in CWs, at Gadenstedt WWTP (Tw = 0.44 Ta, R2 = 0.74)
Various studies have considered the evaluation of the treatment efficiency of
constructed wetlands as a function of temperature depending on components such
as substrate composition, degree of plant growth, seasonal changes in
evapotranspiration rates, and microbial activities (Winthrop et al., 2002). Kadlec and
Reddy (2000) studied the temperature dependence of many individual wetland
processes and wetland removal of contaminants in surface flow wetland. They
concluded that microbial mediated reactions are affected by temperature; the
treatment response was much greater to changes at the lower end of the
temperature scale (<15ºC) than at the optimal range (20 to 35 ºC). Furthermore they
observed that the processes regulating organic matter decomposition were affected
by temperature and so were all the nitrogen cycling reactions (mineralization,
nitrification and denitrification).
With caparisons the fig. of air and water temperature with the fig. of COD, BOD, NH4-
N, TN and TP reduction, it is clearly showed that 94-96% BOD, 86-88% COD is
reduced by microorganism in the period of summer (June, July, August), when water
temperature was 14-18°C. BOD (84-94%) and COD (72-89%) reduced in winter
(January, February and December), when the water temperature was on the range of
5-7°C. Similarly constructed wetlands reduced COD (20-83%), NH4-N (63-70%), and
y = 0,4387x + 6,7985R² = 0,7451
0
2
4
6
8
10
12
14
16
18
20
-5 0 5 10 15 20 25 30
Wat
er
tem
per
atu
re
°C
Air temperature ° C
Air and Water temperature corelation
117 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
TP (74-102%) in summer and COD (34-47%), NH4-N (25-48%), TP (27-47%) in
winter in the case of Berel project.
Fig 9.19: Water temperature of inflow and outflow from SP, CWs, and PP of Berel WWTP
From above data analysis, it can be concluded that temperature affected on the
organic matter (COD, BOD) decomposition and nutrients removable by
microorganism that found maximum in summer and minimum in winter. This is the
very simple way analysis comparing of monthly and seasonally BOD, COD, NH4-N
and TP reduction in percentage with the monthly and seasonally water temperature.
Nutrients reductions are strongly influenced by plants and algal uptake on a seasonal
basis. It is analyzed from above data that Microbial activity is peak in midsummer and
low in winter. These results justified the literature study mentioned above by Kadlec
and Wallace (2009). For the better understanding of temperature effects on pollutants
reduction and efficiency of CWs, it is necessary for the concrete analysis by using
modified Arrhenius equation (Kt = K20 * θ (T-20)) and by tracer method.
9.8 Energy / Power consumption at Gadenstedt and Berel WWTP
Energy is required for the development of different sector like energy consumed 44%
by industry, transportation by 3% and households by 27% and services and
commercials by 26% (AGEB, 2008). Electricity demand in Germany was increased
by 16.8% from 1990 to 2008 and decreased by 7 % from 2008 to 2009
(www.umweltbundesamt.de). Furthermore, as populations growing, more demand for
0
5
10
15
20
25
0 2 4 6 8 10 12 14
°C
Month
Water Temperature
Water temp inflow Water temp effluent of SPWater temp effluent of CWs Water temp effluent of PP
118 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
electricity and continual increases in energy costs which affect the operation and
maintenance cost in wastewater treatment plants. This gives overstress to people to
expense more money on wastewater management. So it is compelled to rethink
about the alternative system of wastewater treatment system not only in Germany but
also in the case of underdeveloped country of Asia, Africa and Latin American.
So it is analysis the data of power consumed by electric pumps, which were installed
in different parts of treatment plants like screening, grit chamber, trickling filter, and
constructed wetlands for the wastewater treatment process. It is only to find out
difference of total annual power consumed and energy cost between the
conventional and constructed wetlands system during the wastewater treatment.
Fig 9.20: Power consumed by conventional system and Constructed Wetlands
From the fig 9.20, power consumed by pumps during the operation periods in the
conventional system in every month is higher than the pumps used in constructed
wetlands. However electricity used by two pump for wastewater lifting, screening,
compressor, sand classifier, sand blower, trickling filter (2 pumps) in the conventional
system and only two pumps are used to pump out water into CWs, which are
collected in collection chamber.
The total power consumed for the wastewater treatment process is 84152 kWh. As
shown in figure 9.21, in which conventional and CWs system consumed about 65060
kWh (77%) and 19092 kWh (23%) respectively. Total annual energy cost is invested
in 14928 € in which conventional system bare 11541.64 € and 3386.92 € by CWs.
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
By Conventional system 8101 6542 6881 4863 4943 4087 3603 3786 4129 4845 6153 7127
By Bodenfilter 1652 1447 1134 1270 1323 1079 1152 1318 1338 1554 2912 2913
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
kWh
Power consumption at Gadenstedt WWTP
119 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Total energy cost to be paid 5.33 € per person (4.12 € for conventional & 1.21€ for
CWs).
Fig 9.21: Energy cost of Gadenstedt WWTP
Similarly, in the case of Berel, one small pumps of 4.5 kW was installed in the
screening to collect the screenable materials and two pumps are used as
alternatively to distribute the wastewater on the CWs as per design hydraulic loading
rate of 59 l/m2.d (average).
Fig 9.22: Power consumed and total power cost for Berel WWTP
Total power consumed by these three pumps are 11078 kWh in the year 2010 and
energy cost be 2077.00 €. Total energy cost is to be paid 3.46 € per person per year,
which is equivalent to 1.22 € / m3, which is very cheap for the wastewater treatment.
77%
23%
Energy cost camparision ,Gadenstedt
By Conventional systemBy Bodenfilter
3386.92 €
11541.64 €
19092 kWh
65060 kWh
Total power cost = 14928 . 56 €
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
By CWs 1835 2576 941 543 484 456 384 384 599 518 2453 538
0
500
1000
1500
2000
2500
3000
kWh
Energy consumption in Berel CWs
120 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Similarly, in comparison to 2002, in Germany municipalities are allowed to pass on
the full cost to the consumer without and profit with average wastewater fee was 2.24
Euro/m3, which translates to an annual cost of 117 euro per person (www.eawag.ch).
According to BDEW, the federal association of the electricity and water industry,
electricity prices for private households rose by 2.1% in the first half of 2010. A
household with three people using 3,500 kWh pays about EUR 69 per month
(www.germanenergyblog.de).
So decentralized system is very fruitful to treat wastewater of small community in the
economic way and helps to preserve the environment with the ecological way also.
9.9 Efficiency of Constructed Wetlands in Germany and Nepal
Germany Nepal
Gadenstedt* Berel** Dhulikhel** Sunga**
in out rem %
in out rem %
in out rem %
in out rem %
mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l
COD 37.87 16.66 56 243.97
39.89 84 325 20 94 1188 50 96
BOD5 8.35 4.40 47 190 12.92 93 110 3 97 450 30 94
NH4-N 1.2 0.61 49 30.71 8.59 72 33 1.6 95 408.9 214.1 48
NO3-N 14.75 6.61 55 26.6 4.34 84 - - - - - -
TN 16.05 7.29 55 - - - - - - - - -
TP 2.47 1.81 26 6.23 2.92 53 8 4 50 44.3 24.3 45
TSS - - - - - - 83 2.3 97 204 28 86
Table 9.4: Summary of removal efficiency of constructed Wetlands in Germany and Nepal. (* as tertiary treatment system, ** as secondary treatment system)
In the given table 9.4, all the data are taken in average inflow and outflow values and
focused to measure the removal efficiency of constructed wetlands. Concentration of
pollutants in wastewater and removal efficiency of CWs at Gadenstedt and Berel are
already discussed in this chapter and similarly in the case of Dhulikhel and Sunga
described detail at chapter 7. But here the main objective of the results analysis is to
compare the treatment efficiency of constructed wetlands between Nepal and
Germany being the different climatic condition.
121 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
The removal efficiency of COD at Gadenstedt and at Berel is found 56% and 84%
respectively. Efficiency of COD reduction at Dhulikhel treatment plan is 94%, which is
38% higher than Gadenstedt and 10% more than Berel. Removal efficiency of COD
at Sunga is about 40 % more than Gadenstedt and 12% more than Berel. Similarly,
BOD reduction is nearly same efficiency between Sunga and Berel and only 3%
difference between Dhulikhel and Berel. 49% NH4-N is reduced by CWs at
Gadenstedt, 72% by Berel, 95% by Dhulikhel and 48% by Sunga respectively.
Similarly, TP reduction at Gadenstedt, Berel, Dhulikhel and Sunga are found 26%,
53%, 50% and 45% respectively.
This is demonstrated by removal efficiencies of BOD, COD, ammonium-nitrogen and
phosphorus given in percentage. The removal efficiency of organic compound (COD,
BOD) are high that indicates biological activity increased which is temperature
dependent. According to the Köppen Climate Classification System (1997), the global
climatic regions can be specified by the latitude ranges. Likewise, German lies under
the mid-latitude climate (Europe: 45° - 60° N) and temperate climate occurs and large
seasonal changes between summer and winter, high annual temperature range and
abundant precipitation throughout the year. Whereas, Nepal lies under low-latitude
climate (0° - 30° N and S) and partially part is under subtropical climate region. Major
climate characteristic are seasonal changes between a very wet, hot and a dry and
cooler period. High and tropical temperatures occurred during the wet season and
high precipitation during the wet season.
It is also noticed that NH4-N and TP removal performance found high in the case of
Berel and Dhulikhel and low in the case of Gadenstedt and Sunga. Nutrients removal
process is largely depend upon the material chosen in bed material and types of
macrophytes used in constructed wetlands. Kadlec and Wallace et.al (2009)
indicated that especially most plant roots are found on the top soil layer at the depth
of 0-10 cm, which helps to remove nutrients with high concentration from this zone by
taking up during the cycle of growth. Phosphorus sorption is heavily influenced by
the presence of calcium carbonate, aluminum oxides and iron oxides and organic
matter in the bed aggregate (Rustige et al., 2003).
Constructed wetlands are in operation in worldwide. However, there is long tradition
in this field especially in the temperate regions like Europe, North America and
122 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
Australia, but many systems have also been constructed and tested in subtropical
and tropical areas, especially in the South Asian and Southeast Asian countries, e.g.
India, Indonesia, Nepal, South China and Thailand, but also in tropical Africa.
9.10 Constructed wetlands as a suitable technology in Nepal
Most of the centrally collected wastewater treatment plants in Nepal are not
functioning due to high cost of operation and maintenance and lack off trained human
resources. To mitigate the financial problem and minimize of water pollution, low-cost
natural treatment options like Constructed Wetlands (CWs) have been introduced in
Nepal since 1997. Due to the success of the first CWs system in Dhulikhel Hospital,
since then, the interest of people has been growing in this technology and more than
a dozen constructed wetlands have been established for various applications such as
the treatment of hospital wastewater, grey water, septage, landfill leachate,
institutional, universities and municipal wastewater.
Table 9.5: Efficiency of CWs and operation cost (UN-HABITAT, 2008 and ENPHO, 2004)
Since 1997 to 2004, there are 12 sub-surface flow constructed wetland systems in
operation for treatment of grey water, wastewater and fecal sludge in Nepal. In
general, the performance of the CWs has been excellent as shown in table 9.5. After
regular monitoring of the systems and analysis of wastewater sample which shows
high pollutant removal efficiency achieving more than 90% removal of TSS, BOD and
COD. Designed system does not need any electric energy as the wastewater is fed
hydro-mechanically into the beds.
Location
TSS Removal Rate (%)
BOD5 Removal Rate (%)
COD Removal Rate (%)
Total cost
US $
O&M cost US $ per annum
Dhulikhel Hospital
97 97 94 27,000 150
Sunga Community
98 97 96 36,111 722
Single house grey water
98 98 94 520 -
Kathmandu University
87 97 93 26,000 290
ENPHO 87 95 88 570 -
SKM hospital
97 98 94 27,000 -
123 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
The total cost of CWs at Dhulikhel hospital including the sewer lines was US$ 27,000
in 1997, while the cost of O&M per year is at US$ 150. For the single house, the
system required an investment of only about US$ 520 (NRs.36, 000) and O&M cost
is very negligible. In SKM hospital, total costs of the system including the sewer lines
were US$ 27,000. In Sunga community, the total cost of the treatment plant was US$
36,111 (NRs. 2.5 million) and average O&M cost of the wetland is about US$ 722
(NRs. 50,000) per year. These projects are an example of an approach towards the
sustainable management of water and wastewater, which has inspired people to
adopt this type of technology that can be managed by the community or institution
itself for the solution of currently mis-managed wastewater in the city.
The popularity of CWs for wastewater treatment are also increasing day by day and
innovative ideas also developed for the treatment of septage and landfill leachate in
the large scale. With this motto, the plant at Pokhara Sub-Metropolitan City was
designed to treat 35 m3 of septage and 40 m3 of landfill leachate per day. It was
estimated that the city generated 12,000 m3 of faecal sludge and 15,600 m3 of
municipal waste every year, all of which would be collected and brought to the site.
The treatment plant comprises of 7 compartmental sludge drying beds (area 1645
m2), 2 compartmental horizontal flow CWs (1180 m2) and 4 compartmental vertical
flow CWs (1500m2). The treatment plant at Pokhara is the largest constructed
wetland in Nepal and it was built at a cost of US$ 85,700 (Rs. 6 million) under the
financial support of Asian Development Bank (ADB). The effectiveness of the
treatment plant has not yet been monitored as it is still not fully operational. It is yet in
observation and however, as experiences from other countries have shown that
constructed wetlands can be used to treat faecal sludge as well landfill leachate, the
treatment plant built in Pokhara can be a model for other cities if it is operated
properly.
Nonetheless, one of the conventional treatment system plant at Guheshwori, the
operation and maintenance cost is estimated NRs 12.5 million per year (US $
167,000 /year) (Richards, 2003). This cost is really very big difference than the
constructed and operation cost of constructed wetlands. So, Constructed wetlands
(CWs) are less expensive for construction, operation & maintenance as compare to
conventional expensive technology as well as higher removal efficiency of pollutants
124 Chapter 9: Results and discussion
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
and utilization of treated effluent for multiple purposes. Therefore, CWs are an
alternative and suitable technology in Nepal, which are considered as effective,
economic and environmentally friendly and sustainable systems for wastewater
treatment.
9.11 Wildlife habitat at Gadenstedt WWTP
Constructed Wetlands and Combined biotopes (Lagoon) at Gadenstedt has been a
new destination to many wildlife habits. Some of the macro invertebrate groups can
be seen in the wetland area, such as Mollusca and insects but there are no
comprehensive lists of even the most common species in these groups. Especially
focus to bird species, about 70 species have been recorded from the Gadenstedt
WWTP and more than 1380 individuals have been caught and ringed. Reed Warbler,
Reed Bunting, Mallard, Greylag Goose and Tufted Duck are dominating bird in the
wetlands area. These are the high bird density (33 – 48 BP/ha.). Some of 27 species
birds are found migrants from the different places of Germany and as well as from
other country during the early spring and summer seasons. Some of them have been
achieved remarkable of long distant migrants from Ibiza, Southern Spain and France.
Fig 9.23: (a) Mr. Matthias Meyer with a Kingfisher in the station. (b) Snails
(invertebrates) on bed, (c) Tufted Ducks swimming at combined biotopes (Lagoon) The water bodies are enriched by nutrients and organic matter from wastewater and
stormwater discharge, which are suitable food chain supply for Tufted Duck and
macroinvertebrate are the main food of other birds in the wetlands area. There is no
hunting but consequent bird protection system. Some of artificial nest are provided
for the breeding process focus to Weißstorch birds. The diversity and abundance of
birds in and around wetlands attract the many birds watcher. So, constructed
wetlands are providing benefits beyond effective water treatment, such as wildlife
enhancement and recreational opportunity.
125 Chapter 10: Conclusion and Recommendation
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
10 Conclusion and Recommendation
Constructed wetlands have been evolved during the last five decades into a reliable
treatment technology which can be applied to all types of wastewater including
domestic, industrial and agricultural wastewaters, landfill leachate and stormwater
runoff. Pollution is removed through the processes which are under more controlled
conditions.
These treatment systems are very favorable for use in rural community and semi-
urban areas of low population density, where land is easily available with low price
and can usually be constructed from local materials. Constructed wetlands are very
effective in removing organics and suspended solids, whereas removal of nitrogen is
lower but could be enhanced by using a combination of various types of CWs.
Removal of phosphorus is usually low unless special media with high sorption
capacity are used.
Constructed wetlands require very low or zero energy input and, therefore, the
operation and maintenance costs are much lower compared to conventional
treatment systems. In addition to treatment, constructed wetlands are often designed
as dual- or multipurpose ecosystems which may provide food and habitat for wildlife
and create pleasant landscapes. So Gadenstedt WWTP is one of the tourist
attraction places for many visitors from different country as well as lot of flora and
fauna can be seen.
At Gadenstedt, constructed wetlands are used as tertiary treatment only for polishing
purpose which helps further reduction of organic matter and nutrients from the
wastewater to ensure better surrounding environment of receiving water course. And
the final effluent of CWs can be used for the multipurpose such as irrigation crops,
aquaculture products. However these practices are not in use and directly discharge
to small river Fuhse but it alternatively helps to recharging the ground water. The
concentration of organic matter and nutrients are very less than legal limit of Federal
law and specific limit of Gadenstedt WWTP.
As per trial experiment from December 2001 to April 2002, CWs used as secondary
treatment and removal efficient of COD, BOD5 was found more than 90 % and
126 Chapter 10: Conclusion and Recommendation
Ecological and Economical efficiency of Constructed Wetlands and Transferability of Decentralized Wastewater Treatment Operation to Nepal
nutrients reduction 50% and 30% respectively. So it is recommended that CWs can
be used as secondary treatment to make more sense fulfilling its objective instead of
tertiary treatment and energy cost can be saved. The operation of trickling filter
would be better to close.
At Berel, wastewater is treated with the combination of CWs and pond system. The
treatment process achieves high effective in the reduction of organic matter and
nutrients. Final effluent values of polishing pond are increased than effluent of CWs.
So it is better to divert the effluent of CWs directly into the small river Sangebach
instead of pond 3.
CWs are also very suitable for the application in developing countries where most of
the problems with inadequate sanitation occur. A crucial step for the implementation
of CWs in developing countries is proper technology transfer.
Constructed wetlands (CWs) are an alternative and suitable technology in Nepal,
which are considered as effective, economic and environmentally friendly and
decentralized sustainable systems for wastewater treatment.
127 References
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