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Concept
Trickling filter
Summary
A trickling filter is a type of wastewater treatment system. It consists of a fixed bed of rocks, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media. 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. The treatment of sewage or other wastewater with trickling filters is among the oldest and most well characterized treatment technologies.
The fundamental components of a complete trickling filter system are:
a bed of filter medium upon which a layer of microbial slime is promoted and developed;
an enclosure or a container which houses the bed of filter medium;
a system for distributing the flow of wastewater over the filter medium; and
a system for removing and disposing of any sludge from the treated effluent.
The terms trickle filter, trickling biofilter, biofilter, biological filter and biological trickling filter are often used to refer to a trickling filter. These systems have also been described as roughing filters, intermittent filters, packed media bed filters, alternative septic systems, percolating filters, attached growth processes, and fixed film processes.
Typically, settled sewage flow enters at a high level and flows through the primary settlement tank. The supernatant from the tank flows into a dosing device, often a tipping bucket which delivers flow to the arms of the filter. The flush of water flows through the arms and exits through a series of holes pointing at an angle downwards. This propels the arms around distributing the liquid evenly over the surface of the filter media.
Most are uncovered (unlike the accompanying diagram) and are freely ventilated to the atmosphere.
The removal of pollutants from the waste water stream involves both absorption and adsorption of organic compounds and some inorganic species (such as nitrite and nitrate ions) by the layer of microbial biofilm.
Official source
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