Improving the dewaterability of municipal wastewater sludge and EPS oxidation by PbO₂ anodic electrocatalytic...

Treating municipal sewage sludge characterized by high moisture content and low dewaterability represents a significant economic and operational burden in wastewater management. This study evaluates the performance of an electro-dewatering (EDW) system equipped with a lead dioxide (PbO₂) anode (PbO₂-EDW) to enhance the dewaterability of anaerobically digested sludge. A five-level central composite design (CCD) was applied to model and optimize four key operational parameters, including current density (10-40 mA/cm²), electrode spacing (1-2 cm), sodium sulfate (Na₂SO₄) concentration (0.5-2.5 g/L), and treatment time (7.5-97.5 min), using the reduction in specific resistance to filtration (SRF) as the response variable. The developed CCD model demonstrated high statistical significance (p < 0.0001) with excellent predictive accuracy (R² = 0.9992). Sensitivity analysis identified treatment time as the most influential factor, contributing 67.17% to SRF reduction. Process optimization predicted a maximum SRF reduction of 72% at a current density of 33.3 mA/cm², electrode spacing of 1.87 cm, electrolyte concentration of 2.5 g/L, and treatment time of 97.5 min, which was experimentally validated at 74.2 ± 1.5%. Comparative experiments using a stainless-steel plate electro-dewatering system (SSP-EDW) demonstrated the superior performance of the PbO₂-EDW process, achieving higher chemical oxygen demand (COD) removal (63.3% vs. 25.3%) and substantially lower energy consumption (453 vs. 1352 kWh/m³). Furthermore, the concentration of dissolved lead released during the PbO₂-EDW process (78 μg/L) remained well below the environmental discharge standard (1 mg/L). Post-treatment characterization using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) confirmed sludge floc disruption and extracellular polymeric substance (EPS) degradation, highlighting the effectiveness of the optimized PbO₂-EDW system in improving sludge dewaterability.