Trickling Filters are a unique type of fixed film biological treatment. In a trickling filter, the micro- organisms used to treat the wastewater are attached, or fixed, to a medium as they contact the wastewater. Wastewater applied to a trickling filter has already passed through a mechanical bar screen and/or primary clarifiers. Wastewater is distributed over the top of the medium and slowly trickles through it. The biological growth is attached to the media. This is in contrast to “suspended growth” biological treatment, where the micro-organisms float freely in the wastewater. Trickling filter effluent always passes through a clarifier to allow for capture of solids generated as a result of treating the wastewater. Although these units are referred to as “Trickling Filters,” no physical filtration actually occurs. Instead, contaminants are removed by biological processes.