A concrete or plastic container filled with fine sand. The long contact time between organic pollutants in the water and the filter medium results in the growth of a biofilm-layer on the particle surfaces. This allows the filter to offer both physical filtration and biological removal. Efficient for pathogens, turbidity and color. Pre-treatment (e.g. straining) is required. Key proponent: Jal-TARA filter.
A ready unit might cost USD 12-30 for concrete filters (for 30+ years) or up to USD 75 for plastic filters (for 10+years). But people might be able to build their own filter box, resulting in lower costs. Running costs are negligible.
Similar to central method. Method might be centrally implemented or people might build their own filter unit. Removed turbidity is a good indicator of efficient removal. Quality of filtrate is to be checked regularly. In case of doubt, chlorination advised.
If filter unit is kept open, contaminations (e.g. bird droppings, leaves) may contaminate the filter. Heavy rains may flush out the filter sand.
Pre-treatment, like straining or settling, required. For start-up of biological processes, filtered water not for drinking in first week. Regularly removal of top layer, filter bed must be >50cm. Occasional replacement of full sand column and lids or taps.
Water from biosand filter has usually good quality, makes it easily accepted by users. Users might not be aware of removing top layer after some time, quality of filtered water might be reduced and there might be increased health risk.
No relevant remarks for Biosand filter.