Investigation of thermal alkaline pretreatment of primary and waste activated sludge on the energy efficiency of sludge digestion.

[Display omitted] • pH 11 is the most suitable pH value for the thermal alkaline process (TAP). • Biogas yield of PS after TAP at pH 11 could increase up to 81%. • Biogas yield of WAS after TAP at pH 11 increased up to 72%. • Net electricity generation of WAS after TAP at pH 11 improved up to 43%. • The results are transferable along the 7 WWTPs, and a model WWTP investigated. Because of the naturally limited anaerobic degradability and limited biogas yield of raw sludge (RS), this study aims to increase the biogas production of primary sludge (PS) and waste activated sludge (WAS) by the integration of thermal alkaline process (TAP). PH 11 is confirmed to be the most suitable pH value for the TAP of both sludges. Moreover, with the pretreatment at pH 11 and 160 °C (6 bar) for 30 min, the investigated PSs and WASs achieved an increased biogas production of up to 81 % and 72 %, respectively. The improved net electricity production of WASs after TAP varied between 15–43 % compared to conventional WAS digestion. However, the TAP of PS at pH 11 enhanced the biogas production by 1–81 %, which did not constantly contribute to an improved net electricity production. [ABSTRACT FROM AUTHOR]