chapter  13
28 Pages

Slow Sand Filtration

Aslow sandfilter ismerely a bed of sand, confinedwithin a box, with appurtenances to deliver and remove water. Figure 13.1 illustrates the main elements of the process and technology.

Slow sand consists of a filter box with appurtenances that measure and control flows for the operation, for example, inflow, filtered water drainage, backfilling after scraping, headwater drainage, etc. All of this is to support a biological depth-filtration process, which is within the sand bed, coupled with a straining process, by a layer of material deposited, and perhaps with organism growth. The straining occurs on top of the sand bed, called the schmutzdecke. Slow sand filtration may be characterized as a passive process in that it occurs without operator intervention.