What is the activated sludge process in wastewater treatment?

The activated sludge process is a biological wastewater treatment method using a mixed microbial community to remove organic matter and nutrients. Key components include: aeration tank (where wastewater is mixed with activated sludge containing bacteria, protozoa, and other microorganisms; oxygen is supplied for aerobic degradation), secondary clarifier (allows sludge to settle; clarified water is discharged; settled sludge is recycled back to aeration tank), and return/waste sludge system (maintains optimal biomass concentration; excess sludge is wasted). Microorganisms consume organic pollutants, converting them to CO2, water, and new cell mass. BOD (Biochemical Oxygen Demand) removal typically exceeds 90%. Variations include extended aeration, sequencing batch reactors (SBR), and membrane bioreactors (MBR).