Methods of HHWT

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

Straining

A 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 Agents

To 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.

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.

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.

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

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.

Basic Components of a Continuously Operated Slow Sand Filter

(after AWWA)

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 Filter

The 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 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:

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

STANDING WATER LEVEL- keeps schmutzedecke alive during pause periods

UNDERDRAIN GRAVEL - promotes water flow to the outlet pipe

COARSE SAND – separates fine sand from underdrain gravel

FINE SAND – traps contaminants that pass through schmutzdecke

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

LID – Prevents contaminants from entering the filter

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.

Components of a Kanchan Arsenic Filter

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

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)

Ceramic Filters

The 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 $189.95

https://www.travmed.com/scripts/catalog.epl?product_id=143&category_id=40&moveit=8 (Apr 05)

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 Disinfection

Chemical 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 System

The 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 Disinfectant

Scientists 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)

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

Boiling Water

Boiling 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 Disinfection

SODIS 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 Pasteurization

This 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.

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 Treatment

Ultraviolet 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)