A biosand filter (BSF) is a point-of-use water treatment system adapted from traditional slow sand filters. Biosand filters eliminate pathogens and suspended solids from water using biological and physical processes occurring in sand columns covered with biofilms. BSF has been shown to remove heavy metals, turbidity, bacteria, viruses and protozoa. BSFs also reduce color change, odor and discomfort. Studies have shown a correlation between the use of BSF and decreased incidence of diarrhea. Because of their effectiveness, ease of use, and lack of recurrent costs, biosand filters are often considered appropriate technologies in developing countries. It is estimated that over 200,000 BSF is used worldwide.
Video Biosand filter
Histori
A household biosand filter was proposed by Dr. David Manz in the late 1980s at the University of Calgary, Canada. The system was developed from slow sand filters, a technology that has been used for purification of drinking water since the 1800s. Initial laboratory and field tests were conducted in 1991; the system was patented in 1993 and implemented in the field in Nicaragua. Canada's non-profit Canadian Center for Affordable Water and Sanitation (CAWST) was established jointly in 2001 by David Manz and Camille Dow Baker to promote education and water purification and sanitation training including using this technology, and to further develop it. A private company, Hydraid Biosand Water Filter manufactures and distributes plans for filters.
Maps Biosand filter
Biosand filter components
Biosand filters are usually made of concrete or plastic. At the top of the filter, a sealed cover prevents unwanted contamination and pests from entering the filter. Below, the diffuser plate prevents biofilm disturbance when water is poured into the filter. Water then runs through the sand column, which removes pathogens and suspended solids. Under the sand column, the gravel layer prevents sand from entering the drainage layer and clogging the outlet tubes. Below the dividing layer is a drainage layer composed of rough pebbles that prevent blockage near the base of the outlet tube.
Filtering process
Pathogens and suspended solids are removed by biological and physical processes occurring in the biolayer layer and sand layer. These processes include:
- Mechanical traps: Suspended solids and pathogens trapped in the space between sand grains.
- Predation: The pathogen is consumed by microorganisms in the biolayer.
- Adsorption: Pathogens are absorbed into each other and become suspended solids in water and sand grains.
- Natural Death: The pathogen resolves its life cycle or dies because there is not enough food or oxygen.
Running
The water level (hydraulic head) in the inlet reservoir zone pushes water through the diffuser and filter, then decreases as water flows evenly through the sand. The flow rate slows down because there is little pressure to force water to pass through the filter. The inlet water contains dissolved oxygen, nutrients and contaminants. It provides the oxygen needed by microorganisms in biofilms. Large suspended particles and pathogens are trapped in the upper part of the sand and partially clog the pore space between the sand grains. This causes the flow rate to decrease.
Idle time usually consists of more than 80% of the daily cycle; During this time, the process of attenuation of microbes tends to be significant. Most disappearances occur where water comes into contact with biofilms. The processes occurring in the biofilm have not been identified. When the standing water layer reaches the level of the outlet tube, the flow stops. Ideally, this should be high enough to keep the biofilm in the wet sand layer and allow oxygen to diffuse through the puddle to the biolayer. Period pauses allow microorganisms in the biolayer to consume pathogens and nutrients in the water. The flow rate through the filter is restored when they are consumed. If the gap period is too long, the biolayer will consume all the pathogens and nutrients, and will die, reducing the efficiency of the filter when it is used again. The gap period should be between 1 and 48 hours. Pathogens in non-biological zones die from lack of nutrients and oxygen.
Maintenance
Over time, particles accumulate in between the filter sand grains. As more water is poured, biofilms form along the top of the diffuser plate. Both of these events cause a decrease in flow rate (blockage and bioclogging). Although slower flow rates generally increase water filtration due to idle time [APS1], this may be too slow for user convenience. If the flow rate falls below 0.1 liter/min, it is recommended by CAWST to perform maintenance. "Swirl and dump", or wet cleaning technique, is used to restore the flow rate. Approximately 1 gallon US (3.8 liters) is poured into the filter before it is cleaned (assuming the filter is empty). The top layer of sand then spins in a circular motion. Dirty water from swirling dumped and sand smoothed at the top. This process is repeated until the flow rate is restored. Cleaning the diffuser plate, outlet tube, lid, and filter outer surfaces on a regular basis is also recommended. The long-term sustainability and efficacy of biosand filters depends on the education and support of knowledgeable support personnel.
Contaminant removal
Turbidity
The results for turbidity reduction vary depending on the influenza water clarity. The turbid water contains sand, silt and clay. Feed turbidity in one study ranged from 1.86 to 3.9 NTU. In the water study was obtained from a sample of water treatment plant faucet from three local reservoirs. It was poured through a slow sand filter and the result showed that the turbidity decreased to an average of 1.45 NTU. In another study using surface water, 93% decrease in turbidity was observed. When the biofilm on the sand is ripe, the displacement of the turbidity increases. Although biosand filters remove a lot of turbidity, slow sand filters, which have slower filtration rates, remove more.
Heavy Metal
There is limited research on the removal of heavy metals by biosand filters. In a study conducted in South Africa, the filter released about 64% iron and 5% magnesium.
Bacteria
In laboratory studies, biosand filters have been found to remove about 98-99% of bacteria. In the removal of Escherichia coli it was found that the biosand filter may increase due to biofilm formation for about two months. Deletion after this time ranges from 97 to 99.99% depending on daily water volume and percent of primary waste added. The addition of primary effluent or wastewater facilitates the growth of biofilms that help kill bacteria. Research shows that biosand filters used in the field remove fewer bacteria than those in controlled environments. In a study conducted in 55 Bonao households, the Dominican Republic, the average E. coli reduction was about 93 percent.
Virus
Laboratory tests show that while filters reduce E. coli in significant amounts, they significantly eliminate fewer viruses because the virus is smaller. In a study using bacteriophage, virus removal ranged between 85% and 95% after 45 days of use. A recent study showed that viral removal increased significantly over time, reaching 99.99% after about 150 days.
Protozoa
In one laboratory test, the biosand filter removed more than 99.9% protozoa. In tests for one type of protozoan, Giardia lamblia , the filter was removed 100% for 29 days of use. This removes 99.98% of other protozoan oocysts, Cryptosporidium sp. , probably because of its smaller size. This removal is comparable to a slow sand filter.
Health benefits
Studies in the Dominican Republic and Cambodia conducted by the University of North Carolina and the University of Nevada show that the BSF uses a reduction in the incidence of diarrheal diseases by 47% in all age groups. In a study conducted by CAWST in Haiti, 95% of 187 households believe that their water quality has improved since using a biosand filter to clean it. 80% of users stated that their family's health has improved since implementation. Such health perceptions on the use of biosand filters have proven to be more positive in long-term users.
Biosand filter type
Concrete
Concrete filters, from concrete, are the most widespread biosand filter types. Concrete is generally better for other materials because of its low cost, wide availability and the ability to be built in place. Plans for concrete filters are openly distributed by CAWST. Several versions have been developed. The CAWST version 9 biosand filter is built with a higher maximum loading rate. Although filtered water passes EPA water quality standards, it is not optimal. Recent research has determined that the contact time between water and granular material is the main determinant in purifying water. The CAWST Version 10 biosand filter considers this; the volume of the water reservoir is equal to the pore space volume of the sand layer. The maximum loading rate decreases by 33% to ensure the water is inundated in constant contact with the granular material.
Concrete BioSand filters are usually produced using steel molds. Plans for steel molds are openly distributed by CAWST.
Clean Water for Haiti, a nonprofit organization headquartered in Camp Marie, Haiti produces biosand filters using adaptations of steel molds.
The non-profit organization OHorizons has designed Wood Molds, based on CAWST 10 Version filter, which can serve as a low-cost alternative. Plans for Wood Molds are openly available on the OHorizons website.
Plastic
Plastic filters are constructed from plastic vats, usually formed off-site. The hydrograph biosand filter is constructed from medical grade plastic with ultraviolet resistance. TivaWater is the latest version of plastic biosand filters and has several important improvements.
Stainless Steel
A stainless steel biosand filter developed by engineers at the SM Sehgal Foundation, an Gurugram-based NGO (formerly Gurgaon), India, has been known to perform better than its concrete counterparts and with wider opportunities for applications and adoption in different geographical conditions. The high cost of plastics prevents its use in rural India. Stainless steel filters, called JalKalp, offer improved filtration rates and better portability (rather than concrete models) and better quality control of production. Concrete filters are susceptible to damage and can be difficult to transport due to their weight (65 kg), making them unsuitable especially in rural or remote hills. Common quality problems are variations in construction materials and manufacturing defects. Furthermore, the crystallization due to the salt in the water reduces the life of the concrete filter. Newly developed lightweight (4.5 kg) biosandis steel filters have advantages over concrete filters, addressing each of these deficiencies and providing better quality control. In addition to improving its performance, stainless steel adds strength, reliability, durability, and filter portability. Water quality tests show the effectiveness of JalKalp against E coli, total coliform, turbidity, and iron contamination. This filter integrates the copper bacteria properties with conventional filtration. The introduction of copper foil in the drainage zone of the JalKalp filter has increased the total removal of coliform and E coli by up to 100% of the contaminated water. The S M Sehgal Foundation promotes the model, which does not require elektabilitas, across India through partnership with like-minded organizations to benefit as much as possible of rural families.
There are challenges to creating water biosand filters in developing countries. Many do not have the professional ability to build metal forms to pour concrete into it. Finding the appropriate mesh size to filter sand layers may also be missing. In Nicaragua you may find metal workers who are capable of welding rebar for home construction, but you will not find bending metal sheeting equipment to make metal molds. Sand is not sold in hardware stores like in the United States. Most likely purchased by pickup loads from streambeds or holes and the only available mesh is 1/4 inch which is too big. When traveling to a third world country it may be best to take with you the right mesh screen.
Another problem facing filter use is adoption. Many projects can provide assistance in building water filters and some projects even distribute them but making the host country to use filters requires more dedication. People need to connect with the owner of the water filter to force them to use the device and get them used to it. Otherwise, some filters are left and left unattended in the street. Simply handing filters is not enough to adopt.
References
External links
- Biosand Filter Knowledge Base containing the latest technical and implementation information, research and project information
- CAWST Biosand Filter contains training and educational resources
- Manz Water info contains a number of detailed resources related to construction and operation
- BioSand filters
- OHorizons Wood Mold BioSand Filter contains technical resources on Construction of Wood Molds for use in the production of BioSand Concrete Filters
- Clean Water for Haiti containing information and resources for biosand filter making
Source of the article : Wikipedia
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