Anaerobic co-digestion of hydrolysate from anaerobically digested sludge with raw waste activated sludge: Feasibility assessment of a new sewage sludge management strategy in the context of a local wastewater treatment plant

Sustainable sewage sludge management is a worldwide issue in wastewater treatment plants (WWTPs). This work developed a new strategy for sewage sludge treatment involving the integration of hydrothermal treatment (HT) with anaerobic co-digestion (AcoD), particularly on the feasibility of mesophilic AcoD of anaerobically digested sludge (DS) hydrolysate and waste activated sludge (WAS). Results show that AcoD of DS hydrolysate from HT 170℃ for 30 min with WAS achieved the highest CH₄ production of 205.39 mL CH₄/g-VS_fed. By adopting the new AD-HT170-AcoD strategy, 61.88 mL CH₄/g-tVS_fed higher CH₄ yield and 22.2% more total solids (TS) reduction were obtained in addition to much better sludge settleability and 7.6% wt. less sludge cake production compared to the conventional mono AD. Although negative energy gain was obtained, the proposed AD-HT170-AcoD strategy is promising, economically feasible, and sustainable when the final sludge disposal of WAS is concerned in the context of whole WWTP.