Sono-Thermal Pretreatment of Waste Activated Sludge for Enhanced Anaerobic Digestion and Volatile Sulfur Compounds Control in Biogas

The impact of sono-thermal pretreatment combining ultrasound and conventional heating as a pretreatment process for municipal waste activated sludge prior to anaerobic digestion is evaluated in terms of sludge solubilization, solids reduction, biogas production, volatile sulfur compounds concentrations in biogas, dewaterability of digested sludge, and economic feasibility of the pretreatment process. A total of nine combined sono-thermal pretreatments were conducted using three different ultrasound specific energy inputs (1000, 5000, and 10,000 kJ kg−1TSS−1) and thermal pretreatment temperatures (50, 70 and 90°C). Results of pretreatment have shown that the sono-thermal pretreatments have significantly reduced VSS after pretreatment ranging from 29%-38%. A maximum of 30% increase in methane production was observed for three pretreatment at 90°C followed by ultrasound pretreatment at 10,000 kJ kg−1TSS−1 specific energy input. Economic assessment suggests that combination of low temperature thermal pretreatment at 50°C and low specific energy input at 1000 kJ kg−1 TSS−1 is economically more feasible compared to ultrasound pretreatment alone.