Description:
In this study, a PbO2 plate electrode was synthesized and optimized for the electrochemical treatment application of waste activated sludge from a municipal wastewater treatment . The sludge dewaterability and mass reduction with different electrolysis time and voltage were quantified to evaluate the treatment efficiency. The mechanism of cell breaking was studied by evaluating different electrochemical oxidation pathways. Results showed that the electrochemical treatment at a voltage of 25 V and electrolysis time of 120 min decreased the dewatering rate of sludge by 35.9%, and the concentration of mixed liquor suspended solids (MLSS) was reduced by 33.7%. Using Scanning Electron Microscope (SEM) and Cell fluorescence staining experiments the impact on the integrity of sludge cells was evaluated. Results showed that electrochemical process clearly destroyed the sludge cell structure and lead to the cell death . Further investigation revealed that hydroxyl radicals (·OH) and sulfate radicals (SO4·- ) produced during the electrochemical treatment played a major role in the cell wall-breaking, while chloride ions (Cl- ) in the electrolyte significantly enhanced the effect due to formation of chloride-related oxidants. The PbO2 electrode was modified by reduced graphene oxide (RGO) to improve the ·OH production capacity. Results showed that the PbO2 (0.05 RGO by wt.%) electrode had the highest ·OH production rate (81.7 μmol/(cm2 ·min)). The electrode improved the removal of MLSS and MLVSS by 11.3% and 11.5%, respectively. And the sludge dewatering and cell destruction were enhanced by 7% and 15.1%, respectively. Adding more NaCl was confirmed as an effective and readily methods to improve the electrochemical performance of sludge treatment mainly due to the higher content of active Cl- species formed