Optimization of biological enzymes combined with Fe²⁺-activated advanced oxidation process for waste activated sludge conditioning using the response surface method

Waste activated sludge (WAS) conditioning is crucial for enhancing sludge dewaterability and effectively reducing the management cost. The feasibility of bio-enzymes with Fe2+-activated advanced oxidation processes (AOPs) for WAS conditioning was investigated in this study. Two representative bio-enzymes, α-amylase and neutral protease, and two typical AOPs, the Fenton system and Fe2+/Ca(ClO)2 system, were chosen. The medical dosages of AOPs were first optimized by single-factor experiments. On this basis, the dosages of bio-enzyme, ferrous ion, and oxidant were optimized using the response surface method (RSM). Results showed that neutral protease combined with the Fe2+/Ca(ClO)2 system performed better in CST and SRF reduction rates while reducing the medical dosages of AOPs. Under the optimal conditions of neutral protease dosage of 20.9 mg/g TSS, Fe2+ dosage of 0.64 mmol/g TSS, and Ca(ClO)2 dosage of 0.54 mmol/g TSS, the reduction in sludge CST and SRF reached 84.81 % and 94.06 %, respectively. The neutral protease with the Fe2+/Ca(ClO)2 system was a potential method for improving sludge dewatering performance.