In wastewater treatment, sludge refers to a composition of various sludge streams from the wastewater treatment plant (e.g. primary and secondary sludge as well as co-substrates). It is treated in an anaerobic process in the digester.
During the fermentation process, anaerobic bacteria hydrolyze complex organic compounds to form simple compounds and subsequently reduce them to organic acids. These organic acids are further converted into methane gas, carbon dioxide and water in the methanogenic phase.
The remaining sludge mass is considered to be stabilized when the proportion of organic matter has been reduced to approx. 45 - 55%. After retention in the digester, the discharged sludge is usually referred to as sewage sludge. After completion of the process, the digested sludge / sewage sludge is conveyed to further treatment steps.


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