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BACKWASH OF GRANULAR FILTERS USED IN WASTEWATER FILTRATION
Citation:
Cleasby, J. AND E. Baumann. BACKWASH OF GRANULAR FILTERS USED IN WASTEWATER FILTRATION. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/2-77/016.
Description:
The use of deep granular filters in waste treatment is of growing importance. The key to long-term operating success of such filters is proper bed design and adequate bed cleaning during backwashing. Cleaning granular filters by water backwash alone to fluidize the filter bed is inherently a weak cleaning method because particle collisions do not occur in a fluidized bed and thus abrasion between the filter grains is negligible. Due to the inherent weakness of water backwashing cited above, auxiliary means of improving filter bed cleaning are essential for wastewater filters. Three auxiliary methods were compared in a wastewater pilot filtration study. The most effective backwash was provided by air scour and water backwash simultaneously at subfluidization velocities. The other two methods, surface and subsurface wash auxiliary or air scour prior to water fluidization wash were about comparable in effectiveness. The performance of coarse sand, dual-, and triple-media filters was compared, and the backwashing routines appropriate for each media are discussed. A number of investigations concerning the design and backwashing of dual media filters are presented.