Formation, extracellular polymeric substances, and structural stability of aerobic granules enhanced by granular activated carbon

Granular activated carbon (GAC) has been proved to accelerate the formation of aerobic granules during wastewater treatment. However, there has never been a study on the extracellular polymeric substances (EPS) or structural stability of the GAC aerobic granules. Thus, this study evaluated the impact of GAC on these characteristics. With GAC addition, granules matured 12days earlier than those of the control group. Scanning electron microscopy showed the surface of aerobic granules enhanced by GAC to be denser and smoother than the surface of control granules, which could be the first line of defense against external selection pressure. After granules matured, there was no difference in contamination removal between the two types of granules. The protein content in EPS of GAC aerobic granules was higher than that of the control group; however, there was no difference in the polysaccharide content. EPS fluorescence in situ staining demonstrated that inside the aerobic granules, a high concentration of protein encapsulated the GAC. In addition, integrity coefficients indicated that GAC significantly improved the ability of aerobic granules to resist hydraulic shear. The result of hydrolase treatment proved that the outer layer structure of the GAC aerobic granules was maintained by -polysaccharide, and the inner layer structure was maintained by protein. The ability of GAC-enhanced aerobic granules to resist single hydrolase was stronger than that of the control group.