Electrochemically driven Fe⁰-activated sulfite oxidation for enhancing sludge dewaterability

Sulfate radical (SO₄^·-)-based advanced oxidation processes (SR-AOPs) are promising for sludge dewatering. In this work, an electrochemically driven Fe⁰-activated sulfite system (E/Fe/sulfite) was developed and demonstrated for sustainably releasing Fe²⁺ to activate sulfite for dewatering waste activated sludge. Under the optimal conditions (sulfite dosage = 40 mg/g dry solids, current density = 30 mA/cm², pH = 6, and time = 60 min), the reduction of capillary suction time and water content of sludge cake were 87.9 ± 2.8 % and 73.1 ± 0.8 %, respectively. The improved dewatering performance was attributed to the degradation of tightly-bound extracellular polymeric substances, along with the decreased live/dead cell ratio and the increased permeability of sludge flocs. The thermal effect (∼21–59 °C) in the E/Fe/sulfite system accelerated the release of intracellular proteins, which could be effectively degraded by the strong oxidizing SO₄^·-. The results also suggested that electrochemical oxidation and thermal effect in the E/Fe/sulfite system had a synergistic impact on improving sludge dewaterability. According to the density functional theory calculation, the hydrophobic amino acids produced from protein degradation were favorable for forming the drainage channels and enhancing sludge dewaterability. This study provides new insights for understanding the SR-AOPs and their applications to sludge treatment.