Effect of Ultrasonic Pretreatment of Sewage Sludge on the Performance of Bioelectrochemical Anaerobic Digester

Objectives:This study examined the effect of ultrasonic pretreatment on primary sewage sludge (raw sludge) solubilization and its subsequent microbial electrolysis cells (MECs) operation performance. Methods:To compare the effect of ultrasound on raw sludge solubilization, ultrasonic pretreatment was conducted at 1~4 W/mL energy density for 5~30 min. In MECs operation, raw sludge was used as a control group, and ultrasound pretreated sludge was used as an experimental group. For comparing MECs performance, biogas production, and organic matter removal were analyzed. Results and Discussion:The optimal experimental condition for ultrasonic pretreatment were 30 min of sonication time at 3 W/mL. In methane production, MEC with ultrasound pretreatment (MEC 3W) produced 243 mL/L more methane than that of unpretreated MEC (MEC) by 4,970 mL/L at 1, 3 cycles. In the modified Gompertz model analysis, the lag phase of MEC 3W was 0.46 days, which was 0.12 days longer than MEC. The maximum methane production rate of MEC 3W by 938.5 mL/L/day was also higher than MEC. MEC 3W showed a 1.8% higher TS removal rate, 2.4% VS removal rate than MEC. COD removal rate also improved by 2.0% when ultrasound pretreatment was applied. The methane yield of MEC with ultrasound pretreatment (377.4 mL/g VSin.) was 0.4% higher than that of MEC without pretreatment. Conclusion:Ultrasonic pretreatment of sewage sludge improved the methane production and organic removal in microbial electrolysis cells. It is necessary to find the optimal operating conditions to obtain the maximize the performance.