Effects of carrier surface hydrophilic modification on sludge granulation: From sludge characteristics, extracellular polymeric substances, and microbial community.

Aerobic granular sludge (AGS) is a powerful biotechnological tool capable of treating multiple pollutants simultaneously. However, the granulation process and pollutant removal efficiency still need to be further improved. In this study, FeO- and MnO-surface-modified straw foam-based AGS (FeO@SF-AGS and MnO@SF-AGS), with an average particle size of 3 mm, were developed and evaluated. The results showed that surface modification reduced the hydrophobic groups of carriers, facilitating the attachment and proliferation of microorganisms. Notably, MnO@SF-AGS showed excellent granulation performance, reaching a stable state about one week earlier than the unmodified SF-AGS. The polymeric substance content of MnO@SF-AGS was found to be 1.28 times higher than that of the control group. Furthermore, the removal rates for NH-N, TN, and TP were enhanced by 27.28%, 12.8%, and 32.14%, respectively. The bacterial communities exhibited significant variations in response to different surface modifications of AGS, with genera such as Saprospiraceae, Terrimonas, and Ferruginibacter playing a crucial role in the formation of AGS and the removal of pollutants specifically in MnO@SF-AGS. The charge transfer of metal ions of MnO@SF promotes the granulation process and pollutant removal. These results highlight that MnO@SF-AGS is an effective strategy for improving nitrogen and phosphorus removal efficiency from wastewater.