A "'trickling filter "'is a type of wastewater treatment system first used by Dibden and Clowes It consists of a fixed bed of Aerobic conditions are maintained by splashing, diffusion, and either by forced-air flowing through the bed or natural convection of air if the filter medium is porous.
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This triggered a decision in 2000 to gradually transfer the responsibility for sanitation in small and medium-sized towns to the national utility ONEP . In 2009 the latter has built or was in the process of building 43 plants, mostly using the stabilization pond technology, but also one activated sludge plant and a few trickling filter plants.
