What is activated sludge?

Activated sludge refers specifically to a mixed culture of microorganisms used in the treatment of wastewater. This process plays a crucial role in secondary treatment, where the primary goal is to reduce organic matter present in the effluent. The microorganisms in activated sludge break down organic pollutants by metabolizing them, thus purifying the water before it is discharged or further treated.

In an activated sludge system, the wastewater is aerated to facilitate the growth and reproduction of these microorganisms, creating a flocculent mass that can effectively settle out from the treated water. The combination of aeration and microbial digestion not only reduces the biochemical oxygen demand (BOD) of the wastewater but also allows for the removal of suspended solids.

Each of the other options describes different components or processes in wastewater treatment but does not accurately define activated sludge. Solid waste, chemicals for disinfection, and filter mediums each play roles in the broader context of wastewater treatment, but they do not encompass the specific function of activated sludge as a biological treatment method.