Coupling microwave irradiation with peroxymonosulfate activation for sludge deep dewatering via enhancing internal bound water removal

Abstract

Excess sludge deep dewatering remains a significant challenge for wastewater treatment sector due to the strong binding of internal bound water within sludge flocs. This study proposes a novel coupling system that synergizes microwave (MW) irradiation with peroxymonosulfate (PMS) activation to enhance the release and removal of internal bound water. By optimizing key parameters, including PMS dosage and MW irradiation time, the results demonstrated that the MW + PMS treatment reduced sludge moisture content from 85.9 % to 64.8 %. In comparison, sole MW or PMS treatments achieved water content reduction to only 84.1 % and 83.1 %, respectively. Electron paramagnetic resonance tests revealed the generation and accumulation of various reactive oxygen species, including ·OH, SO₄^-· and ¹O₂, confirming the efficient activation of PMS. These oxidative species play a crucial role in breaking down extracellular polymeric substance network and microbial cell structure, thereby facilitating internal bound water release. Low-field nuclear magnetic resonance characterization further verified the effective conversion of tightly bound water to more mobile forms. Morphological and thermodynamic analysis indicated that the MW + PMS treatment induced a reduction in the sludge particle size and an increase in surface hydrophobicity. These changes resulted in the formation of cracks during filtration, enhancing water permeability and favoring its removal. More importantly, Lewis's acid-base interaction was identified as the leading force contributing to sludge flocculation and dewatering. This study may provide guidance for developing effective sludge deep dewatering technology.