Which biological process is commonly used in secondary treatment of wastewater?

The activated sludge process is commonly used in the secondary treatment of wastewater due to its effectiveness in reducing organic matter and pollutants through biological means. In this process, microorganisms, primarily bacteria, are introduced into wastewater. These microorganisms consume the organic pollutants present in the wastewater as food, converting them into biomass, which helps in the clarification of the liquid.

The activated sludge process typically involves aeration tanks where air is supplied to promote the growth of these microorganisms. After sufficient time, this mixture of wastewater and microorganisms is then transferred to a settling tank, where the biomass can be separated from the clarified water. This separation allows for the potential recycling of a portion of the biomass back into the aeration tank to maintain the microbial population, while the treated effluent moves on to further treatment stages.

This method is highly advantageous because it not only effectively reduces biochemical oxygen demand (BOD) but also supports the removal of nitrogen and phosphorus through additional processes. Other methods like filtration or disinfection are generally utilized as either pre-treatment or tertiary treatment processes rather than the primary biological mechanism in secondary treatment.