Experimental Optimization of Waste Activated Sludge Disintegration in Pilot Scale Dark Electro-Fenton Process

The pretreatment of waste-activated sludge (WAS) has attracted more attention to reduce relative treatment costs of thickening, digestion, and dewatering. The investigation focused on the pretreatment of WAS using a pilot scale dark electro-Fenton process equipped with a 3-pair cast iron electrode for the first time, explicitly assessing the disintegration and dewaterability of sludge. The impact of operational factors of pH, current density, and reaction time on disintegration degree (DD), volatile suspended solid solubilization yield (VSY), and capillary suction time (CST) was optimized using response surface methodology as a tool for optimizing multiple variables. The experimental variables included pH (2, 3, 4, 5, 6), reaction time (20, 40, 60, 80, 100 min) and current density (4, 12, 20, 28, 36 mA/cm²). The results of 20 experimental runs were evaluated using ANOVA and 2D and 3D plots. Optimization was done by considering the maximization of pH, DD and VSY and minimization of reaction time, current density and CST. The optimum condition was a pH of 4.36, a reaction time of 58.6 min, and a current density of 26.26 mA/cm². The effects of pretreatments under the optimum conditions resulted in 18.08%, 36.96%, and 47.7 s for DD, VSY, and CST, respectively. The concentration of soluble chemical oxygen demand was elevated from 158 to 4179 mg/L through sludge pretreatment under optimum conditions. This will result in more efficient performance and savings in sludge digesting operations.