Sludge treatment

Sludge from the primary sedimentation tanks is thickened and sent to the digester. A small part of the active sludge (surplus sludge) is withdrawn form the activated sludge process and thickened in centrifuges. This thickened active sludge is also transferred to the digester. Anaerobic^* micro organisms degrades the thickened sludges in the digester This results in the releases of biogas. The biogas is used as fuel to drive electricity generators. The remaining sludge digested sludge is dewatered and transported for incineration.

*Anaerobic: According to wastewater treatment terminology, an anaeraobic process do not require oxygen or nitrate, moreover oxygen might even be toxic for some of these processes.