Understanding the role of extracellular polymeric substances in the rheological properties of aerobic granular sludge.

The gel-properties of aerobic granular sludge could sustain the mechanical strength and stability of granules during the operation of wastewater treatment. The contributing extracellular polymeric substances to the gel strength of aerobic granular sludge were verified from the perspective of rheological properties in this study. Moreover, the correlations between the molecular structure and gel properties of extracellular polymeric substances were established by analyzing rheological properties and spectrum results of extracellular polymeric substances extracted by various extraction methods. The results indicated that protein and polysaccharide were indispensable to maintain the cross-linking structure of extracellular polymeric substances. The gel strength of extracellular polymeric substances was positively correlated with the amount of α-helix of natural protein and intermolecular hydrogen bond between each component. The cation exchange resin method which retained the relatively higher ratio of α-helix of natural protein and intermolecular hydrogen bond could better preserve the gel properties of the original aerobic granular sludge. This study could provide a theoretical reference for the cultivation of aerobic granular sludge and the optimization of operating conditions of the reactor.