Enhancement of biological sludge dewaterability by a bipolar electro-dewatering system: process modeling and optimization using CCD-genetic algorithm method

Wastewater treatment leads to the production of large amounts of biological sludge, which is characterized by poor dewatering. The aim of this study was to evaluate the efficiency of a bipolar electro-dewatering system (Bipolar-EDW) to improve the dewaterability of extended aeration system sludge of a local municipal wastewater treatment plant. All EDW experiments were performed in a batch rectangular cube reactor equipped with stainless-steel electrodes. The effect of four independent variables on the reduction of sludge-specific resistance to filtration (SRF) was modeled and optimized by the central composite design-genetic algorithm (CCD-GA). The results of this study showed that the quadratic model is able to predict the EDW process efficiency well with high accuracy (p-value < 0.0001 and R-2 > 0.99). According to the CCD-GA method, the optimal points in the EDW process for cell voltage, electrode distance, NaCl electrolyte concentration, and process time were 34.5 V, 1.85 cm, 250 mM, and 45.5 min, respectively. Under these conditions, the maximum predicted and experimental SRF reductions were 68.8% and 63.4%, respectively. Under optimal conditions, the chemical oxygen demand (COD) concentration of sludge decreased by about 21% after conditioning by the EDW process. The reduction efficiency of total and fecal coliforms (TC and FC) was also 1 log (90%). Heavy metal concentrations were also significantly reduced in the conditioned sludge. FESEM, XRD, and FTIR analysis confirmed the breakage of sludge flocs and the removal of extracellular polymeric substances (EPSs), especially proteins.