Improved dewaterability of anaerobically digested sludge and compositional changes in extracellular polymeric substances by indigenous persulfate activation

Abstract

In this study, an indigenous activation of persulfate by iron-bearing minerals was examined using peroxymonosulfate (PMS) and peroxydisulfate (PDS) for the dewaterability and extracellular polymeric substances (EPS) composition of anaerobically digested sludge (ADS). Iron minerals originally present in the ADS seemed to operate as an initiator of the persulfate activation, which was indicated by an increase in the total dissolved iron in the supernatant. The PMS showed higher performance in improving the ADS dewaterability compared to the PDS, with more reduction in the average microbial flocs size. The extracted EPS consisted of three different fluorescent components of tryptophan-like (C1), humic-like (C2), and fulvic-like (C3) components. In the tightly bound (TB)-EPS, two humic-like components (C2 and C3), which were resistant to degradation, exhibited a strong linkage with dewaterability; whereas, in both the PMS and the PDS systems, the C1 was preferentially degraded by the radical-based oxidation, with a greater extent for the PMS-based treatments. The results showed that prior to the actual EPS degradation, the produced radicals were initially involved in cell disruption. The SEC results during the oxidation clearly demonstrated the degradation of a large-sized biopolymer fraction, followed by the production of relatively small sized molecules. They also revealed in the TB-EPS a close association between the ADS dewaterability and the degradation of humic substances.