Performances of anaerobic digestion of thermal pretreated sludge and characterization of its supernatant fluid

Sewage sludge was pretreated by using thermal hydrolysis process before anaerobic digestion. The digested sludge (dry-solids of 12%) was thermally pretreated at 121°C with a holding time of 30min. The results showed that both the anaerobic digestion performance of thermally hydrolyzed sludge and treatment efficiency of the system are improved. COD and VS removal rates increased from 37.6% and 28.6% to 48.2% and 42.3%, respectively. The biogas per gram of COD added were increased from 273.8mL/gTCOD to 358.3mL/gTCOD, and the yield from the system during 10 days increased by 83.9% over the control. Biogas cumulative volumes and rates in the process of digestion could fit well with specific fountions, respectively. The light density of supernatant fluid from anaerobic digestor indicated the value of E2 and SUVA254 from the pretreated sludge one was appropriately higher than the control one. The E₄/E₆ values showed humic acid generated from anaerobic digested sludge was similar to one from refuse composting, however, had a lower degree of molecular weight compared to one from soil. It concluded that the content of humic acid produced from the pretreated sludge was more than the control.