Electrochemical pretreatment to improve the biodegradability and valorization of waste activated sludge from aerobic wastewater treatment plants

Waste activated sludge (WAS) represents a significant operational and environmental challenge for wastewater treatment plants (WWTPs) due to its low biodegradability, attributed to extracellular polymeric substances (EPS) that hinder enzymatic hydrolysis. Electrochemical (EC) pretreatment has shown promise in improving organic matter solubilization. However, conventional systems often face limitations related to high energy demand, mineralization of organic matter and electrode degradation. This study evaluates EC pretreatment with two dimensionally stable anodes, Ti/RuO₂ and Ti/RuO₂-ZrO₂-Sb₂O₅, as scalable alternatives for improving WAS biodegradability and energy recovery. The EC with both electrodes using WAS as the sole electrolyte, with an applied current of 10 mA/cm² for 30 min, achieved significantly enhanced solubilization with minimal mineralization. This effectively enhances the anaerobic biodegradability of WAS and increases methane recovery while maintaining low energy consumption and avoiding chemical additives. Methane yields increased to 168 and 342 N-L_CH4/kg_VS for WAS pretreated with Ti/RuO₂ and Ti/RuO₂-ZrO₂-Sb₂O₅, respectively, compared to 85 N-L_CH4/kg_VS for untreated sludge. Energy analysis revealed a net gain of 1.64 kW-h/kg_VS, outperforming other EC systems reported in the literature. In this sense, the implementation of this process could be integrated at an industrial scale in WWTPs as a cost-effective strategy for sludge valorization and resource recovery, in line with circular economy principles.