Thermal Pretreatment of Sewage Sludge to Enhance Anaerobic Digestion: A Review

This review summarizes the effect of high- and low-temperature thermal pretreatment (TPT) on sludge dewaterability, anaerobic digestion (AD), and biogas production efficiencies. The AD of the TPT sludge has demonstrated the following observations: reduced sludge retention time, increased biogas generation, higher organics degradation, improved dewaterability, and lower digester volume than the conventional AD of sludge. Energy balance of the TPT process was energetically self-sustainable and produced surplus energy at solids concentration greater than 3%. Net energy and energy ratio of TPT and AD revealed that net energy and energy ratio are increased with increase in total solids concentration.