Effect of Graphene Oxide on the Characteristics and Mechanisms of Phosphorus Removal in Aerobic Granular Sludge: Case Report

Effects of graphene oxide (GO) on phosphorus removal characteristics and mechanisms of aerobic granular sludge (AGS) were investigated in controlled batch tests. The scanning electron microscope (SEM) image results showed that the surface of AGS appeared wrinkled with coccus and bacillus brevis being wizened and the fungal mycelium being cut into pieces in AGS with 0.06 g/L GO. The anaerobic and aerobic batch tests suggested that the net phosphorus uptake of AGS was 2.60 mg/L for AGS with GO, compared with the value (4.38 mg/L) without GO, and the maximum release and uptake phosphorus rates also remarkably decreased. Intracellular and extracellular phosphorus contents were reduced to 64.67 and 19.74% of that without GO, indicating the nanoparticle might have great effects on extracellular phosphorus. The standards, measurements, and testing (SMT) analysis suggested that the inorganic phosphorus (IP) and organic phosphorus (OP) content decreased compared with the values without GO. The summation of phosphorus fraction associated with Ca (Ca-P) and the phosphorus fraction associated with Al, Fe, and Mn (Fe/Al-P) were 82.09% (without GO) and 94.27% (with GO), suggesting the presence of GO resulted in the decrease of content and species of IP. The extracellular polymeric substances (EPS) were reduced from 173.68 mg/g MLVSS to 137.55 mg/g MLVSS when AGS contacted with GO. The results of this assay had uncovered that 0.06 g/L GO could inhibit the bioactivity of phosphorus-accumulating organisms (PAOs), which resulted in the decrease of Ca-P, Fe/Al-P, and OP. EPS played an essential role on the phosphorus removal and granular stability. The decrease of EPS, which was produced by microorganisms, was contributed to decrease of extracellular phosphorus. This study provided an extensive insight into the influence of GO on phosphorus removal mechanism by AGS. Graphical Abstract The influence of graphene oxide on the extracellular polymeric substances and phosphorus species