The fate of extracellular proteins and polysaccharides of waste activated sludge oxidative in aqueous and granular sludge phase upon degradation using Fe(II)-persulfate conditioning

Abstract

Dissolved organic matter, particularly proteins (PN) and polysaccharides (PS) in extracellular polymeric substances (EPS), are regarded as the key factors influencing the dewaterability of waste activated sludge (WAS). An investigation was conducted on the treatment of WAS by Fe(II) activated sodium persulfate (SPS) to evaluate the kinetics of oxidative degradation of EPS in the aqueous and granular sludge phase, and to quantify the oxidation of SPS in aqueous and granular sludge phase in Fe(II)-SPS system. The WAS was divided into granular sludge (GS) and raw sludge filtrate (RSF) by filtration and elutriation. The PN and PS components underwent rapid degradation on treatment with Fe(II)-SPS, which followed pseudo-first-order kinetics for both GS and RSF. EPS protein was preferentially oxidatively degraded over EPS polysaccharide in the same phase system. However, the degradation rates of PN and PS in GS were 1/6 and 16 times higher than those in RSF, respectively. 23% of the sodium persulfate was consumed by all the substances in the bulk solution where the GS was located, reducing the amount of “effective free radicals” that degrade EPS in the system. The mass balance of PN and PS indicated that the use of Fe(II)-SPS conditioning has an obvious degradative effect on EPS, and PN and PS in WAS were oxidized by 76.2% and 58.3%, respectively. These findings provide mechanistic insight into the oxidation and competitive reactions of PN and PS between sludge aqueous and granular sludge phases, which is beneficial to the selection and optimization of sludge conditioning.