Module

1.81.8 Household Water Treatment Processes Water treatment is usually accomplished in a series of steps which are used in both large water treatment plants as well as in household water treatment.

Conventional water treatment plants and large pipeline distribution systems are designed for large town or city uses. However, there are large portions of the world’s population who do not have access to these large systems.

There are affordable water treatment processes that have been developed and proven for use in household or ‘point of use’ applications.

This module will explain various water treatment processes, the pros and cons, and the best application for each process. Criteria for evaluating various

processes for a particular application will be discussed. These criteria can be used as a basis to select an appropriate technology.

Module 1.8 Household Water Treatment Processes

1.8 HOUSEHOLD WATER TREATMENT PROCESSES..........................................1

WATER TREATMENT PROCESSES......................................................................................2Sedimentation................................................................................................................2Filtration.......................................................................................................................3Disinfection...................................................................................................................3

HOUSEHOLD WATER TREATMENT....................................................................................4HOUSEHOLD SEDIMENTATION..........................................................................................4

Straining........................................................................................................................5The 3-pot system............................................................................................................5Coagulant Agents..........................................................................................................5

FILTRATION.......................................................................................................................6RAPID SAND FILTER.........................................................................................................7SLOW SAND FILTER..........................................................................................................7

Pathogen Removal........................................................................................................7Bacteria.........................................................................................................................8Viruses...........................................................................................................................8Protozoa........................................................................................................................8Helminths......................................................................................................................8

BIOSAND FILTER...............................................................................................................9KANCHAN ARSENIC FILTER............................................................................................11OTHER FILTERS...............................................................................................................12

Ceramic Filters...........................................................................................................13Katadyn Drip Filter (ceramic Candle Filter with Plastic Bucket).............................13

DISINFECTION.................................................................................................................14Chemical Disinfection.................................................................................................14CDC Safe Water System..............................................................................................14PuR - Coagulant and Disinfectant............................................................................14Boiling Water..............................................................................................................16Solar Water Disinfection.............................................................................................16Water Pasteurization...................................................................................................16Ultraviolet Light Treatment........................................................................................17

TECHNOLOGY COMPARISON...........................................................................................17Resources........................................................................................................................19

Water Treatment Processes

Raw water is usually treated in three main processes in order to make it safe for human consumption. These processes are used in series starting with sedimentation, then filtration, and followed by disinfection.

SedimentationIf the water contains suspended materials such as particles of sand, clay and other materials, they can be substantially removed with very little energy by allowing the water

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to settle for some period of time. This is accomplished through the use of a natural reservoir, settling pond, or a large tank. When considering household water treatment, even a small container such as a pail will allow a majority of the particles to settle.The sedimentation process can be accelerated through the use of coagulants and flocculants. These are natural and synthetic chemicals that change the electrical charges of the suspended materials. This allows the particles to join together, thereby increasing their mass so that they settle to the bottom of the container. Bacteria and viruses are often attached to particle surfaces. Removal of particles by sedimentation will produce a marked reduction in bacterial concentrations.

FiltrationFilters remove pathogens in several ways. These include straining, where the particles or larger pathogens such as worms become trapped in the small spaces between the grains of filter media; adsorption, where pathogens become attached to the filter media; or biologic processes, where pathogens die naturally or the micro organisms which live in the filter consume the pathogens.

DisinfectionDisinfection comes about primarily through the destruction of the organism cell walls by oxidation. This oxidation is normally a result of the addition of chemicals such as chlorine. It can also be induced by ultraviolet radiation such as natural sunlight or artificial UV rays.

Pathogens can hide from disinfecting agents in organic and inorganic residue in the water. Removal of suspended materials by sedimentation and filtration greatly improves the performance of chemical disinfection agents.

The following is a schematic drawing explaining the basic steps involved in a typical commercial or municipal water treatment process.

A Typical Conventional Water Treatment Plant Process(Figure9.1, Droste: Theory and Practice - Water and Wastewater Treatment, 96)

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After initial screening at the inlet to remove the larger rock fragments and debris, chemical coagulants are added to and mixed rapidly with the water. The mixture is then mixed more slowly in the flocculation tank so that the suspended particles in the water form larger particles. These large particles are then allowed to settle out in the sedimentation basin. Filtration follows sedimentation. There are two principal alternatives with respect to filtration; slow sand or rapid sand filtration. Rapid sand filtration is the most commonly used. The filtered water is then disinfected before distribution and use.

Household Water Treatment

In many parts of the world, the individual household is often responsible for treating its own drinking water. This reality has advantages and disadvantages depending on the location and resources available to the householders. Where community utility water treatment and distribution systems do not exist, it is frequently the only choice other than using untreated water.

Advantages: only choice other than untreated water usually less expensive faster to implement lower water volumes need to be treated entry point for hygiene and sanitation connections

Disadvantages: requires operation and maintenance knowledge requires motivation to ensure required maintenance is done

The daily water consumption for people connected to a piped water system ranges between 80 to 200 litres per person, whereas for people not connected to a piped water system, the daily consumption of water is primarily for essential purposes and this generally ranges between 5 and 10 litres per person. Therefore, a typical family of five would use about 40 litres of water daily for essential purposes.

In the following material of this module, we will attempt to address household water use and treatment systems.

Household Sedimentation

Water storage to allow for settling of suspended particles is a simple method to improve the water quality. Plain sedimentation, however, can only partly remove turbidity – which is a measure of suspended solids – and faecal coliforms – the common indicator used to

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quantify the degree of faecal pollution. The main health risk associated with household water storage is the risk of recontamination through inappropriate handling practices.

StrainingA cloth fabric can be used to strain particles out of water. The following is a presentation that discusses cholera in detail, but it does have a reference to the use of old sari cloth in Bangladesh for straining water. If the cloth is folded such that there are eight layers, the filtering of the cholera organisms can be very effective, and can reduce the outbreaks of cholera.http://www.nsf.gov/od/lpa/forum/colwell/rc021023swedishacadmy.htm (Apr 05)

The 3-pot system If untreated water is drawn, stored, and allowed to stand for a long time, some bacteria/viruses are known to die off. This system is suitable at a household level and is done in the following sequence:

1. Two big pots are used for fetching water on alternative days.2. The first pot is allowed to stand for 24 hours.3. Then the clear top water is carefully poured into a smaller pot for drinking, and

the remaining water used for washing.4. When the first pot is empty, it is cleaned, refilled, and allowed to stand for 24

hours.In this way each day’s water has been standing for 24 hours (one day) before it is used.

Coagulant AgentsTo encourage settling of suspended particles, various additives can be put into the water.A coagulant is a material which forms a gelatinous precipitate in water which then collects fine particles that are too small to filter. This results in a large particle that can be removed by settling and/or filtration.

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Two common chemical coagulants are alum (aluminium sulphate) and PAC (poly aluminium chloride) also known as liquid alum. Many other aluminium or iron salts are commonly used in industrial water treating systems.

Native plants have traditionally been used to improve the quality of the water in a number of countries in Africa and Latin America. For example, the seeds of the Moringa Oleifera are commonly used in Guatemala and Africa as coagulant aids to clarify water. Dried beans (Vicia Fava) and peach seeds (Percica Vulgaris) also have been used in Bolivia and other countries for this purpose.

The seeds of many plants native to the South American continent contain essential oils and have other properties that have been exploited by traditional cultures for centuries. Among these is the ability of certain seed extracts to flocculate particulates in water. To prepare the seeds for use as a coagulant aid, the following procedure is commonly used:

1. Extract the seeds from the plant or fruit. 2. Dry the seeds for up to three days. 3. Grind dried seeds to a fine powder. 4. Prepare a mixture of water and ground seed material; the volume of water

depends on the type of seed material used (in the case of Moringa oleifera, add 10 cm3 of water for each seed; for peach or bean seeds, add 1 L of water to each 0.3 to 0.5 g of ground seed material).

5. Mix this solution for 5 to 10 minutes; the faster it is stirred, the less time is required.

6. Finally, after the sediments settle, decant the treated water. Testing it for pH, colour, and turbidity is recommended.

7. If the test results are acceptable, the treated water can be used for consumption and other domestic purposes

The following web sites describe how plant seeds can be used as a water coagulant.http://www.oas.org/usde/publications/Unit/oea59e/ch22.htm (Apr 05)http://www.le.ac.uk/engineering/staff/Sutherland/moringa/water/water.htm (Apr 05)http://ces.iisc.ernet.in/energy/water/paper/drinkingwater/simplemethods/technology.html (Apr 05)

Filtration

Water filtration by simple household filters, such as ceramic, stone, and sand filters, will remove a high fraction of solid matter and a large portion of micro organisms. Many of these are commercially produced filters which are relatively costly, but some filters can be made of locally available material.

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Rapid Sand Filter

In the rapid sand filter, water is driven through a sand bed or beds of multimedia, either by gravity or by pressure. Fine solids are entrapped in the filter. Particle removal is primarily a physical process.

Rapid sand filters are inappropriate for many applications in developing countries because of their construction cost, their complexity and their need for regular ‘backwashing’ (or rapid flow reversal) at regular intervals to clean the filter.

Slow Sand Filter

The other filtration alternative is a slow sand filter where the water moves slowly through a sand bed. Suspended material is removed by the physical removal of the material and pathogen removal is due primarily to biologic processes in a biologic layer, or schmutzdecke, which develops close to the surface of the sand. Slow sand filters have been in use for over 150 years. They are simple to build and operate, and also improve the microbiological quality of the water substantially. Virtually complete removal of indicator organisms and pathogens, including bacteria, cysts, protozoa, viruses and helminths, has been shown by many researchers.

Pathogen RemovalIn slow sand filters, organic material gets trapped at the surface, or very close to the surface of the sand. Over a period of approximately three weeks, micro organisms colonize the filter in this region, given the abundance of organic food and oxygen derived from the water. These micro organisms consume bacteria and other pathogens in the water, thus providing a very effective water treatment process. In addition to this process, which is known as predation, other biologic processes act on the various pathogens in the water. These processes are summarized below.

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This is one suggested type of a household rapid sand filter but there are few references that indicate its use and acceptance by users.

Module 1.8 Household Water Treatment Processes

BacteriaBacteria are usually between 0.2 and 5 microns long (Brock and Madigan, 1991), much smaller than the spaces between sand grains which are normally in the range of 10 to 20 microns. Bacterial cells are also nearly the same density as water. Bacteria, however, normally grow attached to surfaces, covering the particle surface to form a biofilm. Bacteria by themselves are too small to be removed by straining and too light to be removed by sedimentation. However, they are generally associated with larger particles which are removed by straining or sedimentation, producing a marked reduction in bacterial concentrations.

VirusesViruses can range in size from 0.02 to 0.2 microns. In conventional water treatment, the virus particles are clumped together using coagulants and then settled or strained out. In slow sand filtration, the viruses are adsorbed or become attached to the sand grains. Once attached, they are metabolized by the cells or inactivated by antiviral chemicals produced by the micro organisms in the filter (Ellis ’85 in Buzunis ’95).

ProtozoaIn conventional water treatment, cysts are removed in a manner similar to viruses. However, a small variation in turbidity will result in large fluctuations in cyst concentrations. Some of the recent interest in slow sand filtration has been sparked by the more effective removal of cysts by slow sand filters. Cysts, unlike other pathogens, are highly resistive to common disinfectants such as chlorine, iodine, ozone and ultraviolet radiation.

HelminthsThese worms are generally of sufficient size that they can be removed through straining or sedimentation.

Basic Components of a Continuously Operated Slow Sand Filter

(after AWWA)

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In a conventional slow sand process, the water is continuously fed to the filter. Thus, a pump or gravity flow system with large inlet and outlet storage tanks is required.

The following is a proposed design of a small slow sand filter. However, there are not any references of such a system being used in a household service.

Continuously Operated Household Slow Sand Filter

A small, plastic SSF can be obtained from Blackburn and Associates in California. http://www.slowsandfilter.com/ (Apr 05)

Biosand FilterThe major benefits of slow sand filtration are due to the microbiology of the filter. The microbiological community must be kept alive for the filter to be effective. In a conventional slow sand filter, oxygen is supplied to the organisms through dissolved oxygen in the water. Consequently, they are designed to be operated continuously. Also, because the water moves through at a slow rate, the filter beds tend to be very large.

The BioSand water filter is an adaptation of the traditional slow sand filters in such a way that the filters can be built on a smaller scale and can be operated intermittently. These modifications make the filter suitable for use at the household or small group level - uses which are simply not possible with conventional slow sand filtration because of the size requirements and the mode of operation.

A bucket of contaminated water can be poured into the top of the BioSand filter as necessary. The water simply flows through the filter and is collected in another bucket or

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container at the base of the spout. It normally takes a few minutes for the entire bucket to make its way through the filter because it is designed such that the flow through the filter does not exceed 10 litres/minute/square metre. There are no valves or moving parts and the design of the outlet system ensures that a minimum water depth of five centimetres is maintained over the sand when the filter is not in use. The filtration processes are identical to that of a conventional slow sand filter.

When the water is flowing through the filter, oxygen is supplied to the biologic layer at the top of the sand by the dissolved oxygen in the water. During pause times, when the water is not flowing, the oxygen is obtained by diffusion from the air and by slow convective mixing of the layer of water above the sand (the supernatant). If this layer is kept small in depth, enough oxygen is able to pass through to the micro organisms to keep them alive and thus effective.

The main components of the BioSand filter and their uses are described below:

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LID – Prevents contaminants from entering the filter

DIFFUSER - Protects the schmutzedecke from damage when water is poured in

STANDING WATER LEVEL- keeps schmutzedecke alive during pause periods

FINE SAND – traps contaminants that pass through schmutzdecke

UNDERDRAIN GRAVEL - promotes water flow to the outlet pipe

OUTLET PIPE- Conducts water from the bottom of the filter to the outside – maintains the water level constant

COARSE SAND – separates fine sand from underdrain gravel

Module 1.8 Household Water Treatment Processes

Kanchan Arsenic Filter

The Kanchan Arsenic Filter (KAF) was developed at Massachusetts Institute of Technology (MIT), in collaboration with the Environment and Public Health Organization (ENPHO) of Nepal. The filter can remove both microbial and arsenic contamination. The KAF is a household-level slow sand filter with additional arsenic removal capability. The design of this filter is similar to the Biosand Filter, but the diffuser plated is replaced by a deep diffuser basin filled with 5 kg of non-galvanized iron nails and a layer of brick chips. In addition to the concrete version of the filter, the MIT-ENPHO team has developed a small plastic version using off-the-shelf plastic water buckets available in Nepal.

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Diffuser Basin

Lid

Container

Pipe

Gravel

Coarse Sand

Water

Fine Sand

Iron Nails

Brick chips

Gravel

Coarse Sand

Water

Fine Sand

Iron Nails

Brick chips

Components of a Kanchan Arsenic Filter

Plastic Kanchan Arsenic Filters in Nepal showing the iron nails and brick chips in the diffuser basin

Module 1.8 Household Water Treatment Processes

The iron nails in the diffuser basin, after contact with water and air, will quickly rust. Iron rust (ferric hydroxide) is an excellent adsorbent for arsenic. When arsenic-contaminated water is poured into the filter, arsenic may stay in the diffuser box (i.e. adsorbed to the surface of the rusted nails in the box), or the arsenic-loaded iron particles can be flushed down and trapped on top of fine sand. The purpose of the brick chips is to protect the underlying iron nails from dispersing due to the force of the incoming water.

The KAF can removal 85% to 95% arsenic in the raw water. The iron nails will lose their capacity in 3 to 5 years if the raw water has up to 500 ug/L of arsenic. At that time, replacement of the iron nails is necessary. However, the exact replacement period will depend on a variety of factors such as the usage rate and water chemistry.

Other Filters

In addition to using sand as the filter media, there are other commercially made fabrics or filaments that provide a filtering effect. The following is a description of one such filter. Spiral Wound Cartridge and Charcoal Filter The following water purification system is a simple but effective way to produce potable water. It consists of two five gallon buckets and a sediment filter coupled to an activated carbon filter. The crude water is first chlorinated with approximately 3 cc of commercial bleach per 5 gallons and allowed to sit in a separate bucket for at least 45 minutes to provide ample time for disinfection. It is then poured into the top bucket, where it is filtered through the sediment filter and the activated carbon into the bottom bucket.

The filter units are inexpensive and offer a convenient method of producing potable water. Testing has indicated that the life span of both the carbon and sediment cartridges is considerable -- systems that have been in place for at least two years now are still removing chlorine as efficiently as filters that have been newly distributed. The useful life of the sediment filter varies widely depending on the water that is being filtered.

This is a good filtering system which also uses chlorine and it should give very good quality water. The downside is that the filters elements have to be replaced periodically.http://www.rollins.edu/int-programs/filter.html (Apr 05)

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Ceramic FiltersThe ceramic filter is an old technology and seems to be making a comeback. A piece of ceramic material is constructed such that there are very small pores in the clay/ceramic. When water is allowed to flow the ceramic material, contaminants are trapped in the pore spaces in a similar fashion to a sand filter. If properly construction and operated, a ceramic filter can be very effective in producing good quality water.

Frequently, colloidal silver is added or applied to the ceramic surface. This silver has properties which reduce the bacteria content in water that is in contact with the silver. In its ionic colloid state, silver is recognized as a germicide, or in some cases as bacteriostatic. It is believed that silver is able to disable the particular enzyme that pathogenic bacteria and fungi use for oxygen metabolism, thus suffocating them.Other pathogens are destroyed by the electric charge on the silver particles, causing their internal protoplast to collapse, and still others are rendered unable to reproduce. Parasites are also killed while in their egg stage.

Ceramic water purifiers can be:1. Effective: consistently testing 99 to 100% removal of fecal coliform indicators. 2. Low cost: one new model projected at US$1.50 for the two container system. 3. User friendly.

Potters for Peace is an organization that produces low cost ceramic filters. http://www.potpaz.org/pfpfilters.htm (Apr 05)

This is a very recent web site that describes a ceramic water filter that can be produced for the poor. They are asking for support in testing and documenting the effectiveness of ceramic filters.http://www.purifier.com.np/ (Apr 05)

The following web site is from a commercial manufacturer in Brazil who sells various ceramic filters. He also has distributors in South Africa and Australia. They have silver coated candles as well.http://www.stefani.ind.br (Apr 05)

Katadyn Drip Filter (ceramic Candle Filter with Plastic Bucket)

The heart of the Katadyn Drip Filter is the ceramic element, which will filter particles as small as 0.2 microns, removing all disease-causing bacteria and protozoa. Because the ceramic filter can be cleaned hundreds of times, more water can be filtered at a fraction of the price of a unit with a non-recoverable filter.

The Drip Filter is easy-to-maintain and features no moving parts. It outputs 4 litres per hour, and the service life is 39,000 gallons. A measuring gauge indicates when the filter needs to be replaced. Weight: 7.3 lb. Size: 10" x 18" US $189.95https://www.travmed.com/scripts/catalog.epl?product_id=143&category_id=40&moveit=8 (Apr 05)

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Disinfection

Disinfection comes about primarily through the destruction of the organism cell walls by oxidation. This oxidation is normally a result of the addition of chemicals such as chlorine, bromine, iodine or ozone, or it can be induced using ultraviolet radiation.

Pathogens and other micro-organisms can ‘hide’ from disinfecting agents in organic and inorganic residue in the water. Thus, chemical dosages needed to deactivate or kill pathogens increase with the amount of dissolved or suspended material. Removal of suspended materials by sedimentation and filtration greatly improve the performance of chemical disinfection agents.

Chemical DisinfectionChemical oxidation or disinfection is accomplished by adding a solution of chemical oxidizing agents to the water. With sufficient contact time, chemical reactions occur which change the contaminants in the water. Bleach (chlorine) or sodium hypochlorite addition is the most common chemical oxidation process. It oxidizes organic matter, manganese, iron and hydrogen sulphide.

Water disinfection with chlorine is used to kill micro-organisms (bacteria and viruses), but does not inactivate pathogenic parasites (e.g. Giardia, Cryptosporidium and helminth eggs). This type of treatment requires a supply of chlorine either in liquid or powder form. Skilled application is necessary as chlorine is a hazardous and corrosive substance. Water treated by chlorine has a taste which many users do not appreciate. This table describes the different concentrations of chlorine that are available and how they can be used to make a water treatment solution suitable for household use.

CDC Safe Water SystemThe website below is the CDC Safe Water System manual that describes a program to implement chemical disinfection and safe water storage:Safe Water Systems for the Developing World: A Handbook for Implementing Household-Based Water Treatment and Safe Storage Projects, Department of Health & Human Services, Centers for Disease Control and Prevention (over 200 pages, 2001)http://www.cdc.gov/safewater/manual/sws_manual.pdf (Apr 05)

PuR - Coagulant and DisinfectantScientists from Proctor and Gamble Health Sciences Institute developed a product which consists of powder in a small packet. This powder is made up of a clarifier and a disinfectant (bleach). When added to water and stirred, it coagulates the solid particles and disinfects the water. The water is then strained or decanted to take out the suspended particles. The product is promoted as an affordable and simple-to-use in-home water purification product, PuR Water Purifier. This new purifier clarifies and effectively reduces microbial pathogens, improving the quality of drinking water. Their web site has two short videos about the product and some research testing that has been done.http://www.pghsi.com/communications/pur.htm (Apr 05)

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Source: http://www.who.int/water_sanitation_health/hygiene/emergencies/em2002chap7.pdf

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Boiling WaterBoiling of water kills viral, parasitic and bacterial pathogens. The recommended boiling time is one minute at sea level, adding one minute for every additional 1000 meters in altitude. The main disadvantage of boiling water is the large amount of energy required, making it economically and environmentally unsustainable.

Solar Water DisinfectionSODIS is a simple water treatment method using solar radiation (UV-A light and temperature) to destroy pathogenic bacteria and viruses present in the water. Its efficiency in killing protozoa is dependent on the water temperature reached during solar exposure and on the climatic and weather conditions. Microbiologically contaminated water is poured into transparent containers and exposed to full sunlight for a minimum of 6 hours. Very turbid water with a turbidity of more than 30 NTU cannot be used for SODIS.

SODIS is a water treatment method that: improves the microbiological quality of drinking water does not change the taste of water is applicable at household level is simple in application relies on local resources and renewable energy is replicable with low investment costs is ideal to treat small quantities of water

Sunlight is treating the contaminated water through two synergetic mechanisms: radiation in the spectrum of UV-A (wavelength 320-400nm) and increased water temperature. If the water temperature rises above 50°C, the disinfection process is three times faster.

Limitations of SODIS: does not change the chemical water quality requires relatively clear water (turbidity less than 30 NTU) requires suitable weather conditions is not useful to treat large volumes of water

The following web site is an excellent source of information on the SODIS system. It has a good reference manual, contains lots of technical information, and is easy to use and understand.http://www.sodis.ch/ (Apr 05)

Water PasteurizationThis process achieves the same effect as boiling at temperatures of only 70°C-75°C, but requires a longer exposure time of approximately 10 minutes.

It is essentially a large sized SODIS system. Safe Water Systems uses the time-honoured technique of pasteurization to disinfect water that is microbiologically contaminated.

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Laboratory testing of SWS Solar Water Pasteurizers confirms an effectiveness of 99.999% in disinfecting water that contains disease-causing micro-organisms, including bacteria, viruses, worms and protozoa.

The Family Sol*Saver model disinfects water by combining heat pasteurization with UV radiation. The water is typically heated for 2-3 hours. Once the temperature reaches 62ºC (143ºF), the thermal indicator wax melts, confirming that pasteurization has occurred.http://www.safewatersystems.com/ (Apr 05)

Ultraviolet Light TreatmentUltraviolet water disinfection is not a new technology, but the small-scale, energy-efficient and low-maintenance design has created a uniquely affordable and effective device. Typical systems operate using the equivalent of a 60-Watt light bulb at a cost of as low as 4 cents/ton of water treated, treating 15 Litres/minute, enough for 500-1500 people. As a result, UVW offers the first practical means of providing many communities in developing nations with readily accessible, disinfected drinking water.

Effective on all water-borne bacteria and viruses Inexpensive to buy and operate Simple to use, low maintenance Uses 6,000 times less energy than boiling Accepted by villagers, universal use Works with the flow from a standard hand pump (treats 4 gallons/min)

How it Works UV light disables DNA of micro-organisms in the water Micro-organisms cannot replicate and soon die No effect on taste or smell of water Takes only 12 seconds to treat water

This web site describes an electric ultraviolet device.http://eetd.lbl.gov/iep/archive/uv/ (Apr 05)

This is the web site of the commercial supplier of the household UV system described above. They also sell other types of water treating equipment.http://www.waterhealth.com (Apr 05)

There are several commercial suppliers of UV systems. This site describes a low cost UV Tube that may be suitable for use where there is continuous power. http://www.berkeley.edu/news/media/releases/2003/06/02_water.shtml (Apr 05)

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Technology Comparison

There are several criteria that can be used to assess and compare technologies for treating household water supplies.

A paper by H. Lukacs aims to develop a framework to evaluate the appropriateness of point-of-use treatment technologies for developing country application. An innovative slow sand filtration technology (BioSand filter) is described in this paper and then evaluated based upon these criteria to set a baseline to which other technologies can be compared. The following 10 complementary criteria are expanded upon and their importance to the long-term implementation success of point-of-use water treatment technologies discussed:

Quality of water treated Quantity of water treated Robustness of design Local materials and maintenance Obvious importance to users Local demand for technology Opportunity for community participation Ease of technology transfer Economical sustainability (Capital and Operating Costs) Opportunity for financing

The full text of this paper can be found at this web site:web.mit.edu/11.479/www/Lukacs.doc

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Resources

In the review in the following website, there are several tables where comparisons are made of various household water treatment technologies that are recommended by the author. There is no one “winner”, but the ratings will assist the user in determining which technology might be the most applicable for the particular situation.

This site shows a comparison of various water treating systems. http://www.cdc.gov/safewater/manual/alt_water.htm#figure_19

Within this web site, the following is a page that compares various water disinfection methods.http://www.safewatersystems.com/General%20Pages/Technology%20Comparison%20Chart.htm (Apr 05)

Identifying the most accessible and effective methods for household water storage and treatment are matters of considerable importance and are the subject of the report found at the web site: Managing Water in the Home: Accelerated Health Gains from Improved Water Supply.Geneva, WHO, 2002. WHO/SDE/WSH/02.07. http://www.who.int/water_sanitation_health/dwq/wsh0207/en/ (Apr 05)

This web site contains a number of MIT Master of Engineering theses and other research reports on household water treatment technologies, from technical performance evaluation to social acceptability to marketing strategies.http://web.mit.edu/watsan(Oct 05)

This web site has an interesting article about household based water treatment processes.http://www.skat-foundation.org/publications/pdf/Aguasan_16.pdf (Apr 05)

The following web site is a very extensive list (6,600 listings) of commercial companies from around the world that design and manufacture various pieces of equipment or provide services for the following: environmental information, waste water treatment, water supply and purification, air pollution control.http://www.eco-web.com/ (Apr 05)

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