Mild thermal pre-treatment of waste activated sludge combined with hydrogen peroxide and iron addition

Abstract

This work investigates the effects of mild thermal pre-treatment combined with hydrogen peroxide (H2O2) and iron(II) chloride (FeCl2) dosing on WAS (waste activated sludge) disintegration to boost anaerobic digestion and subsequent energy recovery potential. A two-stage thermal approach was applied, where sludge was first treated at 55 °C with and without chemical additives, followed by further processing at 70 °C. All pre-treatments significantly increased soluble chemical oxygen demand (SCOD), with the highest solubilisation observed under combined FeCl2 and H2O2 addition, suggesting an observable effect of chemical addition on sludge solubilisation. This increase in SCOD was further supported by extracellular polymeric substances (EPS) analysis, which showed a shift from tightly bound to soluble fractions. Additionally, hydrogen production was observed during pre-treatment at 55 °C, with higher yields in the presence of FeCl2 addition. Overall, the results indicated that mild thermo-chemical pre-treatment, particularly with FeCl2 addition, enhanced WAS hydrolysis while enabling hydrogen production, highlighting its potential to improve sludge energy recovery and support more resource-efficient wastewater treatment operations.