Pyrite catalyzed peroxydisulfate for improving dewaterability of waste activated sludge: Reaction sequence of hydrophobic/hydrophilic structures

Dewatering is an essential step for reduction, harmlessness, and resource utilization of waste activated sludge (WAS). In this study, the WAS dewaterability was investigated using pyrite activated peroxydisulfate (PDS) conditioning and the intrinsic mechanism was explored. The experimental results showed that the specific resistance to filtration (SRF) and the sludge water content (Wc) of sludge cake values decreased from 43.17 +/- 1.71 x 10(12) m kg(-1) and 85.94 +/- 0.30% to 2.59 +/- 0.07 x 10(12) m kg(-1 )and 74.39 +/- 0.25% with optimal pyrite and PDS dosages, respectively. The reactive radicals (center dot OH and SO4-center dot) generated through the reaction of pyrite/ PDS destroying the hydrophilic functional groups in the extracellular polymeric substances (EPS), leading to the release of bound water. Besides, the collapse of sludge floc structure and a decrease in the mean particle size of sludge were found. Meanwhile, the smaller value of alpha-helix/(beta-sheet + random coil) reflected that the protein structure was looser and the hydrophobic sites or groups of the proteins were more likely to appear. Further analysis of hydrophobic and hydrophilic structures in the sludge revealed that the hydrophilic substances were exposed first, followed by the protein structure unfolding, causing the exposure of the unsaturated and hydrophobic structures, and thus posing a positive effect on sludge dewaterability. Collectively, this study offered a new alternative to enhance sludge dewaterability through the application of natural minerals.