Electrochemically driven Fe0-activated sulfite oxidation for enhancing sludge dewaterability

Sulfate radical (SO4 center dot-)-based advanced oxidation processes (SR-AOPs) are promising for sludge dewatering. In this work, an electrochemically driven Fe-0-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/cm(2), 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 (similar to 21-59 degrees C) in the E/Fe/sulfite system accelerated the release of intracellular proteins, which could be effectively degraded by the strong oxidizing SO4 center dot-. 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.

Automated summary

An electrochemically driven Fe-0-activated sulfite system was developed to sustainably release Fe2+ for dewatering waste activated sludge. The system improved dewatering performance by degrading extracellular polymeric substances, reducing the live/dead cell ratio, and increasing the permeability of sludge flocs. The thermal effect in the system accelerated the release of intracellular proteins, which could be degraded by the strong oxidizing sulfate radicals. Understanding these sulfate radical-based advanced oxidation processes is important for sludge treatment.