What is a typical method used in secondary treatment processes?

The activated sludge process is a widely used method in secondary treatment processes within wastewater treatment facilities. In this process, microorganisms, primarily bacteria, are utilized to decompose organic matter in the wastewater. The process involves aerating the sewage to promote the growth of these microorganisms, which break down pollutants typically found in the effluent.

After aeration, the mixture containing both the treated wastewater and the biomass (activated sludge) undergoes a sedimentation step, where the heavier sludge settles to the bottom, allowing the clarified water to be separated from the biomass. A portion of this settled sludge is then recycled back into the aeration tank to maintain a sufficient concentration of microorganisms, while the excess is removed for further treatment or disposal.

This method is advantageous because it is highly effective at reducing biochemical oxygen demand (BOD) and total suspended solids (TSS), making it a cornerstone in modern wastewater treatment plants. Other secondary treatment methods, like trickling filters or rotating biological contractors, also exist but are less common compared to the activated sludge process, which is favored for its efficiency and control over the biological treatment of wastewater.