Biosand Water Filters
Watch this short video to learn about the biosand filter and how
together we can bring the gift of clean water to families in
need.
Biosand Water Filter
Over 250,000 filters have been installed in over 50 countries. The Center for Affordable Water and Sanitation Technology (CAWST) oversees this effort. You may visit the CAWST website for further information about the history of the biosand filter and its use around the world. The following is an excerpt from their site:
The Biosand filter is an innovation on traditional slow sand water filters , specifically designed for intermittent or household use. The filter can be produced locally anywhere in the world because it is built using materials that are readily available. It is simply a concrete container, enclosing layers of sand and gravel which trap and eliminate sediments, pathogens and other impurities from the water.
Plastic can also be used to manufacture the container, however, using concrete has several advantages:
How Does it Work?
Water is poured into the top of the filter as needed, where a diffuser plate placed above the sand bed dissipates the initial force of the water. After traveling slowly through the sand bed, the water then passes through a bed of gravel and collects in a pipe at the base of the filter. At this point, the water is propelled through plastic piping encased in the concrete exterior and out of the filter for the user to collect. It should be used with a safe water container, which must have a tight fitting lid and either a narrow mouth or a spigot so that water is poured from the container.
Removal of Contaminants
As with all slow sand filters, a combination of biological and mechanical processes removes pathogens in the water. When water is poured into the top of the filter, the organic material it is carrying is trapped at the surface of the fine sand, forming a biological layer or "schmutzdecke." This biological layer matures over one to three weeks, depending on volume of water put through the filter and the amount of nutrients and micro-organisms in the water.
Four processes remove pathogens and other contaminants in the Biosand filter:
Effectiveness
Slow sand filters have been proven to almost entirely remove the disease-causing organisms found in water. The Biosand filter adaptation has proven as effective as traditional slow sand filters, in both laboratory and field tests. In conjunction with the introduction of the technology to communities, the filter has been tested by various government, research, and health institutions, as well as by non-governmental agencies. CAWST carried out water analyses of 107 long term Biosand filter users in Haiti in 2005 and found average removal effectiveness of 98.5% (measuring E. coli, the indicator bacteria recommended by the WHO). [ Download Executive Summary ]
The filter has also been proven to remove:
CAWST has prepared a summary of laboratory and field studies for the Biosand filter. The body of evidence shows the success of biosand filter implementation since its inception and outlines further challenges to implementation. [ Download Summary ]
Operation and Maintenance
Operation
Operating the filter is very simple: remove the lid, pour a bucket of water into the filter, and immediately collect the treated water in a container. The filter can produce up to 36 litres/hour.
The following design features of the Biosand filter ensure its ease of use:
Maintenance
Continued use of the filter causes the pore openings between the sand grains to become clogged with debris. As a result, the flow rate of water through the filter decreases. Though this does not reduce the ability to remove contaminants, the slow flow rate is likely to frustrate the user.
To clean the filter, the surface of the sand must be agitated, thereby suspending captured material in the standing layer of water. The dirty water can then be easily removed using a small container. The process can be repeated as many times as necessary to regain the desired flow rate. This procedure is sometimes call a "swirl and dump" maintenance practice. The need to do this depends on the amount and quality of water being put through the filter. If the water is relatively clean (turbidity less than 30 NTU), the filter can likely run for several months without this maintenance procedure.
After cleaning, a re-establishment of the biological layer takes place, quickly returning removal efficiency to its previous level.
Further Reading
If you're the curious type and you've still got lots of questions, we suggest you read the Bio-Sand Water Filter Overview.
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Biosand Water Filter
Over 250,000 filters have been installed in over 50 countries. The Center for Affordable Water and Sanitation Technology (CAWST) oversees this effort. You may visit the CAWST website for further information about the history of the biosand filter and its use around the world. The following is an excerpt from their site:
The Biosand filter is an innovation on traditional slow sand water filters , specifically designed for intermittent or household use. The filter can be produced locally anywhere in the world because it is built using materials that are readily available. It is simply a concrete container, enclosing layers of sand and gravel which trap and eliminate sediments, pathogens and other impurities from the water.
Plastic can also be used to manufacture the container, however, using concrete has several advantages:
- Cement can be easily acquired in most developing countries.
- People are familiar with the construction techniques.
- Household labour or volunteer labour can be utilized in the manufacturing process.
- The concrete container is heavy and durable. It does not need to be replaced as often as a plastic container.
- The spout piping is located inside the filter. Consequently, it is less prone to damage than a plastic filter, which has piping on its exterior.
- Plastic fabrication usually requires the importation of raw material or the finished product. Depending on your views of international trade, this can be an advantage or disadvantage.
- The life expectancy of a plastic model is substantially less than a concrete model. The ultimate disposal of plastic is a concern for the environment.
- Encouraging and empowering local people to completely manage their own project increases local sustainability and motivates others to take action for safer water. This process can only be facilitated if the product supply is managed locally. In most cases, if a plastic model is used, there will always be a dependence on outside manufacturers and distributors to supply filters at a higher cost.
How Does it Work?
Water is poured into the top of the filter as needed, where a diffuser plate placed above the sand bed dissipates the initial force of the water. After traveling slowly through the sand bed, the water then passes through a bed of gravel and collects in a pipe at the base of the filter. At this point, the water is propelled through plastic piping encased in the concrete exterior and out of the filter for the user to collect. It should be used with a safe water container, which must have a tight fitting lid and either a narrow mouth or a spigot so that water is poured from the container.
Removal of Contaminants
As with all slow sand filters, a combination of biological and mechanical processes removes pathogens in the water. When water is poured into the top of the filter, the organic material it is carrying is trapped at the surface of the fine sand, forming a biological layer or "schmutzdecke." This biological layer matures over one to three weeks, depending on volume of water put through the filter and the amount of nutrients and micro-organisms in the water.
Four processes remove pathogens and other contaminants in the Biosand filter:
- Mechanical trapping: Sediments, cysts and worms are removed from the water by becoming trapped in the spaces between the sand grains. Over time the spaces become smaller, enabling the filter to trap smaller particles sooner in the sand bed. The filter can remove some inorganic compounds and metals if they are attached to other materials or each other.
- Adsorption or attachment: Viruses are adsorbed or become attached to the sand grains. Once attached, they are metabolized by the cells or are inactivated by antiviral chemicals produced by the organisms in the filter. Certain organic compounds are also adsorbed in the sand and thus removed from the water.
- Predation: The microorganisms within the "schmutzdecke" or biological layer consume bacteria and other pathogens found in the water, thereby providing highly effective water treatment.
- Natural death: Food scarcity, less than optimal temperatures and a relatively short life span will cause pathogens to die off and become nutrients for other micro-organisms.
Effectiveness
Slow sand filters have been proven to almost entirely remove the disease-causing organisms found in water. The Biosand filter adaptation has proven as effective as traditional slow sand filters, in both laboratory and field tests. In conjunction with the introduction of the technology to communities, the filter has been tested by various government, research, and health institutions, as well as by non-governmental agencies. CAWST carried out water analyses of 107 long term Biosand filter users in Haiti in 2005 and found average removal effectiveness of 98.5% (measuring E. coli, the indicator bacteria recommended by the WHO). [ Download Executive Summary ]
The filter has also been proven to remove:
- More than 96% of fecal coliforms
- 100% of protozoa and helminthes
- 50-90% of organic and inorganic toxicants
- Greater than 75% of iron and manganese
- Suspended sediments, in all or part
CAWST has prepared a summary of laboratory and field studies for the Biosand filter. The body of evidence shows the success of biosand filter implementation since its inception and outlines further challenges to implementation. [ Download Summary ]
Operation and Maintenance
Operation
Operating the filter is very simple: remove the lid, pour a bucket of water into the filter, and immediately collect the treated water in a container. The filter can produce up to 36 litres/hour.
The following design features of the Biosand filter ensure its ease of use:
- Water can be filtered as required
- The concrete Biosand filter is devoid of moving parts
- The concrete container is small, but extremely stable; it can be placed anywhere in the home, in the location most convenient to the user
- The plastic piping is encased in concrete and is not easily damaged
- Between uses, a layer of water (5cm deep) is maintained above the sand at all times. It is this design feature that distinguishes the Biosand filter from other slow sand filters, allowing for small scale construction and intermittent use. The layer of water is shallow enough for oxygen to diffuse through, providing the biological layer with enough oxygen to develop.
Maintenance
Continued use of the filter causes the pore openings between the sand grains to become clogged with debris. As a result, the flow rate of water through the filter decreases. Though this does not reduce the ability to remove contaminants, the slow flow rate is likely to frustrate the user.
To clean the filter, the surface of the sand must be agitated, thereby suspending captured material in the standing layer of water. The dirty water can then be easily removed using a small container. The process can be repeated as many times as necessary to regain the desired flow rate. This procedure is sometimes call a "swirl and dump" maintenance practice. The need to do this depends on the amount and quality of water being put through the filter. If the water is relatively clean (turbidity less than 30 NTU), the filter can likely run for several months without this maintenance procedure.
After cleaning, a re-establishment of the biological layer takes place, quickly returning removal efficiency to its previous level.
Further Reading
If you're the curious type and you've still got lots of questions, we suggest you read the Bio-Sand Water Filter Overview.
© 2010 Created by Impact Nations
