A Trickling Filter is a fixed bed, biological filter that operates under (mostly) aerobic conditions. Pre-settled wastewater is ‘trickled’ or sprayed over the filter. As the water migrates through the pores of the filter, organics are degraded by the biomass covering the filter material. The Trickling Filter is filled with a high specific surfaceareamaterial such as rocks, gravel, shredded PVC bottles, or special pre-formed filtermaterial. Amaterial with a specific surface area between 30 and 900m2/m3 is desirable. Pre-treatment is essential to prevent clogging and to ensure efficient treatment. The pre-treated wastewater is ‘trickled’ over the surface of the filter.