Activated sludge is a process used in wastewater treatment to remove organic matter and pollutants. It involves aerating sewage to promote the growth of microorganisms, which consume the waste. These microorganisms form a floc, or clump, that can be easily separated from the treated water. After aeration, the mixture is allowed to settle in a clarifier, where the heavier floc sinks to the bottom. The settled sludge can be recycled back into the aeration tank to maintain the microbial population, while the treated water is discharged or further processed. This method is efficient and widely used in modern wastewater treatment plants.