Analysis Of Anaerobic Digestion Potential For Municipal Sludge And Studies Of Thermal And Ultrasonic Pretreatment On Anaerobic Digestion Performance

Anaerobic digestion technology will be widely applied due to dramatic increase inmunicipal sludge amount and attention of dealing with sludge issue. However it suffersfrom long digestion time, low biogas production, and unstable operation, thereforeadditional pre-treatment is often required for enhancing anaerobic digestion efficiency.In this dissertation the sludge from several wastewater treatment plants (WWTPs) inQingdao city were used for studies to investigate organic contents in primary sludge andsecondary sludge in order to analyze anaerobic digestion potential. The analysis ofanaerobic digestion potential provides for theoretic support for anaerobic digestion formunicipal sludge in Qingdao. Based on the analysis of above anaerobic digestionpotential, secondary sludge from a typical WWTP in Qingdao was taken for studies ofthermal and ultrasound pre-treatment and the combination on disintegration of sludgeflocs and dissolution of organic contents on anaerobic digestion performance. This wasaimed to solve the bottleneck of anaerobic digestion for municipal sludge and providedtechnical support for potential bio-energy recycling and resource utilization. The mainresults of above analysis and studies can be summarized as follows.(1)Investigation in organic contents in municipal sludge from several WWTPs inQingdao has shown that sludge from Haibohe WWTP, Tuandao WWTP, and MeidaoWWTP has organic contents (VS%) as high as around70%VS, with high digestionpotential and biogas production potential, which are suitable for sludge anaerobicdigestion. While sludge from Licunhe WWTP and Loushanhe WWTP have low organiccontents, therefore low potential for anaerobic digestion and biogas production.(2)thermal hydrolysis, ultrasound, and the combination of both for pre-treatmentare effective in disintegration of sludge flocs and dissolution of organic contents insludge to increase soluble COD, soluble protein, and soluble carbon hydrates in liquidphase for enhancing digestion efficiency. For sludge with different total solid (TS)contents, the combination of thermal hydrolysis and ultrasound has better pre-treatmenteffect than thermal hydrolysis and ultrasound alone. Based on the disintegration effectand energy consumption, the best condition for2%TS feeding is thermal hydrolysis for30min and ultrasound energy density as0.5W/mL; the best condition for3%and4%TS feeding is thermal hydrolysis tfor30min and ultrasound energy density as0.3W/mL; the best condition for5%TS feeding is thermal hydrolysis for45min and ultrasound energy density as0.3W/mL.(3)Reasonable increase in digestion temperature and additional pre-treatmentenhanced anaerobic digestion to some extent. The pre-treatment has better effects onbiogas production than increase in digestion temperature does, while increase intemperature for digestion has better effect on shortening digestion time thanpre-treatment has. After pre-treatment the biogas production increased by37.51%anddigestion time is reduced to14days, while increase digestion temperature frommesophilic to thermophilic conditions enhanced biogas production by28.50%andshortening digestion time to11days.