In Trickling Filters, in contrast with bioscrubbers, the processes of gas absorption and liquid phase regeneration occur simultaneously in one process appartus. Trickling filters generally consists of columns filled with packing on whose surface a biofilm or microbial flora several millimeters thick develops.
The specific area of the packing is relatively low. This creates a large void volume for gas passage, thus minimizing both the gas pressure drop in the column and the risk of the void space becoming obstructed by biological growth and loose films.
Water containing dissolved inorganic nutrients is continuously supplied at the upper side of the column and homogeneously distributed over the column cross section. This water flows down in a thin film, which surrounds the packing material and wets the biolayer. The waste gas is forces to rise through the void volume against the water flow.
Water soluble components and oxygen are transferred to the liquid phase, then the biolayer where they are eliminated by aerobic biological reactions. In this way, a continuous driving force for mass transfer of further gaseous compounds into the liquid phase is established.
Slime caused by microbial growth and mineralization of the biofilm may be sloughed off into the liquid phase but this can, if necessary, be withdrawn from the water before recirculation. As a result of evaporation, some fresh water has to be continuously supplied to the system.