Enhancement for the Rupture of Waste Activated Sludge Cells and Directional Methane Conversion Based on Microwave-Fe(II)/S₂O₈ 2− Combined Pretreatment

In this study, the effect of microwave (MW)-Fe(II)/S₂O₈ 2− combined pretreatment on sludge cells rupture, biodegradability and subsequent methane producing potential were investigated. The results demonstrated that single microwave pretreatment could promote the anaerobic digestion of sludge, while the combined process could greatly promote the lysis of sludge cells, shorten the hydraulic retention time, and improve the removal rate of organics. The enhancement effect showed a close correlation with the applied MW power and oxidant dosage. The optimal condition was 2− observed to be MW 640 W and Fe(Ⅱ)/S₂O₈ 0.8/1.0 mmol·g⁻¹-TS. Under this condition, the solubilization degree of the sludge was 7.5-time higher than the control and the peak of methane production in subsequent anaerobic digestion was obtained after only 4 days, with 75.7% shorter start-up time than other samples. Also, the biodegradation of organic matter, especially soluble polysaccharides, reached the highest of up to 98.6%. The further analysis by fitting with the first-order dynamic model demonstrated that the potential of methane production rather than the hydrolysis rate was necessarily related to methane production. Although a net energy output was not realized even under the optimal pretreatment conditions, the current result can save at least 20.1 kWh of specific energy consumption per kilogram dry sludge, which was only 45%—60% of traditional energy consumption.