Sustainable disposal of excess sludge: Post-thermal hydrolysis for anaerobically digested sludge

Post-thermal hydrolysis process (THP) has been suggested for the anaerobic digestion (AD) of excess sludge to improve the performance such as dewaterability and solids reduction. However, the behind mechanism, energy deficit and potential ecological benefits are always ignored. In this study, the effects of post-THP temperature on methane yields, dewatering performance and antibiotic resistance genes (ARGs) of sludge digestate were investigated, and the energy balance of AD-THP setup was also systematically compared. The best results can be obtained at temperatures above 160 °C. The methane yield of liquid hydrolysate increased to 175 mL CH4/g CODadded at the temperature of 160 °C, and the release of soluble protein and extracellular polymeric substances contributed to the improvement, indicating that the recirculation of centrate could benefit the AD-THP system. Post-THP efficiently disintegrated the structure of digestate flocs and increased the dewatering performance of digestate cake by two times. Additionally, the absolute abundance of ARGs was eliminated by more than 3 logs and most residual antibiotics were not detected, lowering the ecological risks for land application of the biosolid products. The energy balance analysis revealed a net energy output up to 372 kW⋅h/t DS, suggesting that AD-THP configuration would be a promising alternative for the sustainable disposal of excess sludge.