Biosand filter
Biosand filters remove pathogens and suspended solids from water using biological and physical processes that take place in a sand column covered with a biofilm.
[3] Because of their effectiveness, ease of use, and lack of recurring costs, biosand filters are often considered appropriate technology in developing countries.
The Canadian non-profit company Center for Affordable Water and Sanitation Technology (CAWST) was co-founded in 2001 by David Manz and Camille Dow Baker to promote education and training in water purification and sanitation including using this technology, and to continue developing it.
[3] Pathogens and suspended solids are removed by biological and physical processes that take place in the biolayer and the sand layer.
Ideally, this should be high enough to keep the biofilm in the sand layer wet and allow oxygen to diffuse through the standing water to the biolayer.
If the pause period is too long, the biolayer will consume all of the pathogens and nutrients and will die, reducing the efficiency of the filter when it is used again.
Although slower flow rates generally improve water filtration due to idle time [APS1], it may become too slow for the users’ convenience.
During each visit, beneficiaries receive repeated instruction about safe water practices and how to take care of the filter.
[7] In removal of Escherichia coli it was found that the biosand filter may increase due to biofilm formation over about two months.
The removal after this time ranged from 97-99.99% depending on the daily water volume and percent primary effluent added.
The addition of primary effluent or waste water facilitates growth of the biofilm which aids bacterial die-off.
[1] Research shows that biosand filters in use in the field remove fewer bacteria than ones in a controlled environment.
[1] A recent study has suggested that virus removal increases significantly over time, reaching 99.99% after approximately 150 days.
[11] In a study conducted by CAWST in Haiti, 95% of 187 households believed their water quality had improved since using biosand filters to clean it.
Concrete is generally preferable to other materials because of the low cost, wide availability and the ability to be constructed on-site.
The maximum loading rate was decreased by 33% to ensure stagnant water is in constant contact with granular material.
[13] The non-profit organization OHorizons has designed a Wood Mold, based on CAWST’s Version 10 filter, which can function as low-cost alternative.
[15] A stainless steel biosand filter developed by engineers at S M Sehgal Foundation, an NGO based in Gurugram (formerly Gurgaon), India, has been found to perform better than its concrete counterparts and with a wider opportunity for application and adoption in different geographical conditions.
The stainless steel filter, called JalKalp, offers increased filtration rate and better portability (than concrete models) and better production quality control.
Concrete filters are prone to breakage and can be difficult to transport due to weight (65 kg), make it unsuitable especially in remote rural or hilly locations.
Water quality tests demonstrate JalKalp's effectiveness against E coli, total coliforms, turbidity, and iron contamination.
Introduction of copper foil in the drainage zone of JalKalp filter has increased the removal of total coliform and E coli to 100% from contaminated water.
S M Sehgal Foundation[16] promotes the model, which required no electricity, across India through partnerships with like-minded organizations to benefit as many rural families as possible.
