Examination on Process Configurations Incorporating Thermal Treatment for Anaerobic Digestion of Sewage Sludge

This study aimed to examine the process configurations for mesophilic anaerobic digestion of sewage sludge, when incorporated with thermal treatment of 120°C for 1h . Four types of process configurations were designed: control (no thermal treatment), pretreatment and posttreatment configurations of the single-stage process, and an interstage-treatment configuration of the two-stage process. The lab-scale digesters were operated at 35°C with the sewage sludge of 4.5% total solids, and were equally set at the total hydraulic retention time of 20 days. At the steady state, the control digester showed 35.3% of volatile solids (VS) destruction and 0.168L∕g VS fed of methane production. Compared to the control, the VS destruction in the pre-, post-, and interstage-treatment configurations was increased by 4.5, 6.6, and 9.9%, respectively, while the methane production in the post- and interstage-treatment configurations was improved by 0.036 and 0.028L∕g VS fed, respectively. The pretreatment configuration yielded identical methane production to the control. Therefore, it is more effective on anaerobic digestibility to apply the moderate thermal treatment after sewage sludge is digested once. On the other hand, the increase in soluble chemical oxygen demand and deterioration of dewaterability were observed, when solids destruction was improved.