The first step in Secondary Treatment at the Oneonta treatment plant is a Fixed Film Reactor . The first treatment is the Trickling Filter in which the wastewater is distributed over a large mass of rocks with microbes growing on the surface. The microbes are used to take in soluble organic matter from the effluent. As the wastewater is being distributed throughout the rock bed, the water is in contact with the air to oxidize the water chemistry. The ammonium is converted to nitrates, and the organic phosphorus is converted to orthophosphate.
Air is required for the growth of the microbes.
As the microbes age they die and slough off the rocks. The trickling filter must be covered to prevent freezing in the winter. A view of an uncovered tricking filter. The stones and water delivery system are visible. This process uses large plastic or synthetic fabric disks which rotate through the wastewater collecting a thin layer of microbes.