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

Abstract

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 °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 °C. THP showed no significant impact on FW with only marginal improvements at 150 °C. Increasing the temperature beyond 170 °C for TWAS and 150 °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 °C with no synergism. Co-digestion of thermally pretreated FW with TWAS improved methane yields by 15% and kinetics by 25% at 150 °C, with improvements up to 21% in synergy. THP of the mixed feedstocks improved methane yields by 53% and kinetics by 92% at 170 °C, with improvements becoming less pronounced with the increase in the volume of FW and temperature.