Effects of carrier surface hydrophilic modification on sludge granulation: From sludge characteristics, extracellular...

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, Fe₂O₃- and MnO₂-surface-modified straw foam-based AGS (Fe₂O₃@SF-AGS and MnO₂@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, MnO₂@SF-AGS showed excellent granulation performance, reaching a stable state about one week earlier than the unmodified SF-AGS. The polymeric substance content of MnO₂@SF-AGS was found to be 1.28 times higher than that of the control group. Furthermore, the removal rates for NH₄⁺-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 MnO₂@SF-AGS. The charge transfer of metal ions of MnO₂@SF promotes the granulation process and pollutant removal. These results highlight that MnO₂@SF-AGS is an effective strategy for improving nitrogen and phosphorus removal efficiency from wastewater.