Anaerobic Digestion: Technical Realizations in Municipal Sludge Treatment

Anaerobic digestion technology is used largely for the stabilization of the municipal sewage sludge resulting from aerobic used water treatment. During this process, part of the organic fraction of the raw sludge is converted into renewable energy thus increasing the overall energy efficiency of the UWTP. A net reduction in the quantity of solids and the destruction of pathogenic organisms also result. Apart from the environmental factors, a number of operational process parameters, including solid retention time, hydraulic retention time, volatile solids reduction, and sludge pretreatment, have a major effect upon digestion performance. Over time many process modifications have been developed. Besides traditional mesophilic single-stage digesters, two-stage digesters, two-phased digestion processes, and temperature-phased digestion processes are applied, whereby a combination of mesophilic and thermophilic range is possible in each stage or phase. In addition, co-digestion, as well as thermal, mechanical, and chemical pretreatment options known as sludge disintegration, can be used to increase the overall performance of the anaerobic digestion process.