Understanding the mechanism in aggregation ability between aerobic and anammox granular sludge from the perspective of exopolysaccharides

Although it has been confirmed that extracellular polymeric substances (EPS) play a critical role in the aggregation of granular sludge, the relative contributions and structural characteristics of different polymer components have not been clarified. Through enzymatic hydrolysis and an aggregation experiment two types of granular sludge with a high aggregation ability (aerobic and anammox granular sludge) were studied. The results showed that the aggregation ability of anammox sludge was higher than that of aerobic granular sludge (AGS), and another discovery is that the aggregation ability of sludge after polysaccharide (PS) hydrolysis was obviously inferior to that after protein (PN) hydrolysis. To go insight into the differences of PS structure and properties, rheology and atomic force microscopy (AFM) were conducted and demonstrated that anammox PS had a higher viscosity, mechanical strength and self-assembly ability (dense three-dimensional structures). Furthermore, size exclusion chromatography (SEC), multiangle laser light scattering (MALLS), refractive index (RI), FTIR and XPS analyses indicated that compared with AGS PS, anammox PS had a higher molecular weight, branched structure, proportion of hydrogen bonds, and hydrophobic component. This study is helpful for fully understanding the structure and properties of PS and can provide theoretical support for the high aggregation performance of granular sludge.