Mechanistic Study on Boron-Doped Diamond Electrode Pretreatment for Enhanced Dewatering of Municipal Sludge

Abstract

The production of municipal sludge is rapidly increasing, and how to dispose of large amounts of sludge has become an important issue 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 as the evaluation index. Under these conditions, the BDD electrode was found to disrupt the extracellular polymers, cell walls, and cell membranes of the microorganisms in the sludge, as demonstrated by the colorimetric methods of Coomassie Brilliant Blue-G250, anthracene ketone, and 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 suggest that the BDD electrode significantly improves the dewatering performance of residual sludge by disrupting bacterial cell structures through the production of ·OH radicals and attacking hydrophilic functional groups, thereby altering the form of water in the sludge.

Keywords: boron-doped diamond electrode, residual sludge, environment, sludge dewatering, low-field NMR, FTIR