AWWA JAW30369

Slow sand filtration may be not only the cheapest and simplest treatment process to operate and maintain but also the most efficient under appropriate circumstances. Limitations of conventional slow sand filters include significant reductions in filter run lengths should raw water turbidity and algal content exceed relatively low levels, poor organic precursor removals, and relatively long filter cleaning downtimes and ripening periods. This review article summarizes and evaluates modifications to slow sand filters that may address these limitations without compromising the simplicity of the treatment process. Successful modifications include roughing filters, filter mats, preozonation, amendments to the surface of the filter (i.e., replacing a layer of sand with a granular medium), and filterschmutzdecke harrowing. A table matches limitations with modifications. Includes 43 references, tables, figures.