Improving energy ratio of ultrasonic pretreatment of waste activated sludge using the combination of potassium permanganate and acidic conditions

Ultrasonication is a widely employed sludge pretreatment method in laboratories, and its applicability in the field is limited due to its low energy ratio. Thus, in this work, an effort was made to reduce the energy consumption of ultrasonication by combining it with potassium permanganate and acidic pH (USMAPP). The optimized conditions of USMAPP were ultrasonic power of 160 W, potassium permanganate dosage of 40 mg/g SS, and pH of 4. The combined pretreatment was efficient, requiring a lower specific energy input of 5647.1 kJ/kg TS to attain a more significant solids reduction and solubilization of 20.54 % and 25.16 % than ultrasonic pretreatment alone (11.9 % and 15.65 %) and ultrasonic mediated potassium permanganate pretreatment (15.24 % and 19.21 %). The greater biogas yield of 371.9 mL/g COD in USMAPP indicates improved solubilization and hydrolysis of sludge. In USMAPP, achieving an energy ratio of 1.08 through combinative pretreatment was possible, making the process viable and applicable at field scale. Energy and economic assessment revealed a net energy production of 26.5 kWh/ton, indicating possible scalability of the process to an industrial level.