Enhancing anaerobic digestion of dewatered sewage sludge through thermal hydrolysis pretreatment: Performance evaluation and microbial community analysis

Abstract

This study explored the effectiveness of thermal hydrolysis (TH) in conditioning dewatered sewage sludge (DSS) for enhanced anaerobic digestion (AD). The TH pretreatment employed in this study (30 min at 170 degrees C and 6 bar) significantly improved the bioavailability of DSS. The degree of solubilization varied with the physicochemical characteristics of DSS collected over three seasons: 16.8-24.8% on a volatile solids (VS) basis and 9.4-33.7% on a chemical oxygen demand (COD) basis. Correspondingly, the dissolved fraction of VS in DSS increased by 2.1-3.4-fold, and the soluble fraction of COD rose by 1.4-2.9-fold. The duplicate anaerobic reactors treating the TH-pretreated DSS did not achieve steady-state operation at the intended design organic loading rate (OLR) of 3.8 g VS/L center dot d, but showed stable performance at an OLR of 3.4 g VS/L center dot d with significantly higher methane yield (0.26-0.29 L/g VS fed) and VS removal (35-38%) than those reported for untreated DSS and comparable to TH-pretreated DSS. The reactors' microbial community structures changed dynamically as the OLR varied, with shifts in dominance between acetoclastic and hydrogenotrophic methanogens. The results highlight the prom-ising potential of TH-AD process for efficiently treating DSS while emphasizing the importance of optimizing OLR for stable operation.