Mechanistic study on boron-doped diamond electrode pretreatment for enhanced dewatering of municipal sludge

The production of municipal sludge is increasing rapidly, and the disposal of large amounts of sludge has become a significant challenge in urban development. This study investigates the mechanism and effect of the dewatering pretreatment of municipal sludge using boron-doped diamond (BDD) electrodes. Orthogonal experiments were designed to determine the optimal current density, temperature, pH, and reaction time, using sludge specific resistance (SSR) as the evaluation index. Under these optimal conditions, the BDD electrode disrupted extracellular polymers, cell walls, and cell membranes of sludge microorganisms, as quantified by Coomassie Brilliant Blue-G250 and anthrone colorimetric methods, alongside UV spectrophotometry. Low-field nuclear magnetic resonance (LF-NMR) T2 patterns revealed the transformation of interstitial water in the sludge to free water. Free radical masking experiments and Fourier transform infrared spectroscopy (FTIR) indicated that the presence of ·OH radicals significantly reduced hydrophilic functional groups (-OH, N-H, C-O, -COOH, and -C-O-C-) in extracellular polymeric substances (EPS), thereby reducing hydrophilicity and enhancing dewatering capacity. These findings demonstrate that BDD electrode treatment significantly enhances sludge dewaterability by generating ·OH radicals, which disrupt cellular structures and attack hydrophilic functional groups in EPS, consequently converting bound water into free water.