Combined thermal hydrolysis pretreatment and anaerobic co-digestion of waste activated sludge and food waste

In this study, the impact of thermal hydrolysis pretreatment (THP) on the mono- and co-digestion of thickened waste activated sludge (TWAS) and food waste (FW) was carried out at temperatures of 150, 170, 190, and 210 degrees C and volumetric ratios of 90:10, 70:30, and 50:50 in batch anaerobic tests. THP enhanced solubilization, reduced volatile suspended solids (VSS) and the particle size of TWAS as the temperature increased showing optimal improvements at 170 degrees C. THP showed no significant impact on FW with only marginal improvements at 150 degrees C. Increasing the temperature beyond 170 degrees C for TWAS and 150 degrees C for FW deteriorated anaerobic biodegradability forming refractory compounds. Co-digestion improved methane yields and kinetics as the contribution of FW increased. Co-digestion of thermally pretreated TWAS with FW improved the methane yields by 27% and kinetics by 29% at 170 degrees C with no synergism. Co-digestion of thermally pretreated FW with TWAS improved methane yields by 15% and kinetics by 25% at 150 degrees C, with improvements up to 21% in synergy. THP of the mixed feedstocks improved methane yields by 53% and kinetics by 92% at 170 degrees C, with improvements becoming less pronounced with the increase in the volume of FW and temperature. (c) 2022 Elsevier Ltd. All rights reserved.