Secondary Wastewater Treatment
Secondary wastewater treatment follows primary wastewater treatment is the biological process of reducing suspended, colloidal, and dissolved organic matter in the effluent from primary treatment systems. Secondary wastewater treatment generally removes 80 to 95 percent of the Biochemical Oxygen Demand (BOD) and suspended matter. Secondary wastewater treatment may also be accomplished by biological or chemical-physical methods. More common means of secondary treatment include activated sludge and trickling filters. Secondary wastewater treatment is accomplished by bringing together wastewater, bacteria, and oxygen in trickling filters or in the activated sludge process. This treatment removes floating and settleable solids and about 90 percent of the oxygen demanding substances and suspended solids. Disinfection is the final stage of secondary treatment.