Alum sludge conditioning with ferrous iron/peroxymonosulfate oxidation: Characterization and mechanism

Alum sludge produced by drinking water plants needs to be conditioned and dewatered before final disposal. In this study, a novel ferrous iron/peroxymonosulfate (PMS) oxidation process was employed to enhance alum sludge dewaterability The effect of oxidative sulfate radicals generated by Fe²⁺ activated HSO₅ ⁻ on alum sludge was studied. The results showed that the optimal conditioning conditions for addition of Fe²⁺ and PMS were 0.5 g/g and 0.1 g/g TSS, respectively. Meanwhile, the capillary suction time (CST) and specific resistance to filtration (SRF) of alum sludge was reduced by 66% and 88%. Also found was that the absolute value of the zeta potential increased and the particle size decreased in alum sludge after Fe^{2 +}-PMS conditioning, which indicated that oxidative sulfate radicals destroyed the floc structure of alum sludge and smaller particles were generated. At the same time, the water contained in sludge flocs was released and enhanced sludge dewaterability, while leaching of aluminum ions also characterized decomposition of alum sludge.