Here the treated water is separated from any remaining solids. These solids primarily consist of microbes which have sloughed off the Trickling Filter and RBC's. The wastewater is held in large holding tanks and the leftover solids are given time to settle to the bottom of the tank where they are piped for sludge treatment. A view of the secondary sedimentation basins. The final step in the secondary treatment process at the Oneonta plant is Disinfection .
Disinfection is done by chlorination.
Chlorine gas kills bacteria that may cause disease. Chlorinating is done only during the summer in order to minimize environmental damage. Chlorine is generally toxic to fish and other aquatic life. While the liquid effluent resulting from Primary Treatment is sent on to Secondary Treatment, the solids, or sludge, goes through further treatment as well. This sludge consists of raw sewage solids and is the most offensive of the sludge.