The novel application of polyoxometalates in sludge dewatering: Cells lysis and re-flocculation

Polyoxometalates (POMs) coupled with FeCl3 was tested as an efficient and eco-friendly sludge dewatering conditioning in this study. The results indicated that the water content of the sludge cake and capillary suction time were reduced from 86.61 % and 51.15 s to 67.68 % and 16.7 s under the optimum POMs and FeCl3 dosages of 1.20 mM/g volatile suspended solids (VSS) and 300 mg/g VSS, respectively. The underlying mechanism of the enhanced sludge dewaterability was elucidated based on the variation of physicochemical properties and extracellular polymeric substances (EPS) fractions of the conditioned sludge. The strong acidity of POMs and its interaction with proteins contributed to tightly bound EPS leaching and cell lysis during POMs/FeCl3 conditioning, which disrupted the sludge flocs structure. POMs denatured the released proteins and exposed the internal hydrophobic groups, enhancing the hydrophobicity of the sludge samples. Likewise, the engagement of POMs with sludge cells promoted the lysis of sludge cells by triggering the inactivation of specific functional enzymes, releasing capillary water, surface bound water, and a portion of the intracellular water. Fe3+ re-flocculated the free EPS with the crushed sludge particles through electrical neutralization to form a rigid porous structure. The cells crushing and re-flocculation effects synergistically enhanced the release efficiency of internal bound water, thus achieving sludge deep dewatering. Moreover, POMs/FeCl3 conditioning decreased the absolute abundance of antibiotic resistance genes (ARGs) and intI1 by disrupting the bacterial hosts, resulting in the removal and oxidation of ARGs and intI1 from the solid phase.