Nearly one-fifth of the world's population lacks access to safe, reliable sources of drinking water. Point of use (POU) household water treatment technology allows people to improve the quality of their water by treating it in the home. A promising emerging POU technology is the biosand filter (BSF). The BSF is a household-scale, intermittently operated slow sand filter that maintains a wet media bed containing a schmutzdecke and allows periodic water dosing by the user. Step input chemical tracer tests indicated that the BSF operates at near-plug flow conditions. Six-to-eight week longitudinal challenge studies were conducted with daily charges of surface water spiked with E. coli strain B bacteria, coliphages MS2 and PRD-1 and human enteric virus echovirus type 12. The BSF ripened in a manner similar to conventional SSFs. Flow rate slowed and microbial reductions improved over time with ripening. E. coli reductions were ~90% following filter startup but improved to 95—99.5% over time. Microbial reductions were greater with greater residence time within the filter, especially for water retained in the filter bed overnight. E. coli and echovirus 12 reductions were greater than those of coliphages MS2 and PRD-1.
Elliott, M.A., C.E. Stauber, F. Koksal, K.R. Liang, D.K. Huslage, F.A. DiGiano and M.D. Sobsey. The operation, flow conditions and microbial reductions of an intermittently operated, household-scale slow sand filter. In Recent Progress in Slow Sand and Alternative Biofiltration Processes. Edited by R. Gimbel, N.J.D. Graham and M.R. Collins. International Water Association. London, 2006.