Improving the energy balance between microwave pretreatment and anaerobic digestion with centrifuged biosludge

The effect of pretreatment of raw biosludge (Bs) and centrifuged Bs (CBs) with microwave (MW) operated at constant conditions before an anaerobic digestion (AD) process on the energy requirement and production of hybrid system was investigated. With the successful breakdown of Bs and CBs by the MW irradiation, the soluble COD concentrations increased from average value of about 76 mg/L to 300 mg/L and 6400 mg/L for the Bs and CBs, respectively. After the MW disintegration, the protein and sugar concentrations were about 10 and 22 times higher in the pretreated samples compared to the biosludges. While, the total and volatile solids (TS and VS) concentrations in the liquor declined. The increase of readily bioavailable organics in pretreated samples improved about 22% CH₄ production in AD units, compared to the raw Bs and CBs. It was determined that the energy requirement of MW irradiation decreased about 3 times with the centrifugation of Bs. Although the applied whole models were well correlation, the kinetic analysis showed that Transference Function was the best model with the highest correlation coefficient (R² between 0.953 and 0.998) for predicting the most accurately CH₄ production. The nutrients concentrations in effluent of AD process was significantly higher than the liquors obtained after the MW irradiation was observed.