Activated sludge
Activated sludge or activated sludge is the name given to the accumulation of microorganisms that break down organic substances during aerobic biological wastewater treatment . It mainly consists of bacteria , fungi and protozoa .
The activated sludge is responsible for nitrification in the sewage treatment plant in the activated sludge process . Above all, it is important to provide him with sufficient oxygen. After the cleaning process, the activated sludge is separated from the wastewater and reused as sewage sludge .
Return sludge
The return sludge (also return sludge or recirculation sludge) is part of the activated sludge that is created in the activated sludge tank. This is separated from the treated wastewater in the secondary treatment. The usually good settling behavior of the activated sludge is used to separate it from the treated wastewater by sedimentation. Most of this sludge is returned to the aeration tank as return sludge. This ensures that the activated sludge concentration in the activated sludge tank can be maintained. The revitalized flakes contained in the return sludge renew the cleaning power of the revitalization. The smaller volume flow of the activated sludge that is not recirculated is called excess sludge.
Excess sludge
The excess sludge is the part of the activated sludge that is drawn off to keep the desired biomass concentration constant and pumped into the sludge treatment. This removed biomass increment is usually fed together with the primary sludge to sludge digestion and finally to sludge dewatering.