The purpose of this study was to assess the nutrient salts removal efficiency and stability of the aerobic granular sludge (AGS) by change in C/N (carbon to nitrogen) ratio. The laboratory-scale experiments were performed to analyze the removal efficiencies for organic matter and contents of nitrogen, MLSS, sludge volume index, and extracellular polymeric substances (EPS) under C/N ratio conditions of 5.0, 10.0, 15.0, and 20.0. The microorganisms were observed using optical microscope and the microbial communities were analyzed using pyrosequencing. The increase in C/N ratio from 5.0 to 20.0 increased the organic matter and nitrogen removal efficiency to 95.9 and 79.1%, respectively. For the EPS contents, an influencing factor of granule stability, the polysaccharides to protein (PS/PN) ratio increased from 0.55 to 0.79. For the microbial community, the <i>Thauera</i> was the most common genus in ending phase occupying 63.7%. This microorganism is regarded as one contributing to organic matter degradation and improved production of EPS including AGS of microorganism, thus, may be an explanation of the results of this study such as increase in organic material in AGS and improvement of denitrification efficiency and contents of EPS with increase in C/N ratio.

This study investigated the characteristic of aerobic granular sludge (AGS) process to treat the sewage having low carbon/nitrogen ratio (Biochemical oxygen demand (BOD5):Total nitrogen (T-N), 4.5:1) in sequencing batch reactor (SBR). The removal efficiency of BOD5, suspended solid (SS), T-N and phosphorus (PO4 3-P) were 92.6%, 64.3% and 90.1%. Concentration and size of AGS were changed in proportion to the organic matters and nitrogen concentration of the influent (Concentration and size of AGS: 1,700-3,000 mg/L, 0.5-1.0 mm). Mixed liquor suspended solid (MLSS) also changed with the concentration of AGS (MLSS: 2,000-3,500 mg/L). When the settling time was shortened from 15 min to 10 min, size and shape of AGS were maintained (Size of AGS: 1.0-1.5 mm). In addition, the concentration of AGS and MLSS increased (Concentration of AGS: 3,500 mg/L, MLSS: 4,000 mg/L). Concentration, size and shape of AGS were affected the settling time of the reactor more than the concentration of organic matter and nitrogen in the influent. In the results of removal efficiency and changes in AGS, we confirmed that the SBR process using AGS can be used to treat the sewage having low carbon/nitrogen ratio by applying short settling time.

The wastewater generated in methylcellulose (MC) production is characterized by high salinity and pH due to the residual sodium and chlorine separated from the methyl group. It is difficult to treat wastewater using the conventional activated sludge method because the high concentration of salt interferes with the microbial activity. This study confirms the biological removal of organic matter from MC wastewater using sludge dominated by Halomonas spp., a halophilic microorganism. The influent was mixed with MC wastewater and epichlorohydrin (ECH) wastewater in a 1:9 ratio and operated using a sequencing batch reactor with a hydraulic retention time of 27.8 d based on the MC wastewater. The removal efficiency of chemical oxygen demand (COD) increased from 80.4% to 93.5%, and removal efficiency had improved by adding nutrients such as nitrogen and phosphorus to the wastewater. In terms of microbial community change, Halomonas spp. decreased from 43.26% to 0.11%, whereas Marinobacter spp. and Methylophaga spp. increased from 0.50% to 15.12% and 7.51%, respectively.

This study investigated the biological treatment of high-salinity wastewater using aerobic granular sludge (AGS). The removal performance, AGS characteristics, and microbial community were examined under salinity conditions ranging from 0.5 to 3.0 wt.%. When the salinity was increased, the removal efficiency of the chemical oxygen demand did not change substantially. The mean removal efficiency of NH₄⁺-N ranged from 43.7 to 72.6% during the operation period. As for the concentration of extracellular polymeric substances (EPS), the polysaccharide/protein (PS/PN) ratio increased from 0.37 to 0.57. The concentrations of the mixed liquor suspended solid (MLSS) and mixed liquor volatile suspended solid (MLVSS) were 4,560 and 3,170 mg/L, respectively, in the end phase, and the MLVSS/MLSS ratio decreased from 0.81 to 0.69. The sludge volume index (SVI₃₀) decreased linearly from 88 to 58 mL/g. In the microbial community analysis, <i>Nitrosomonas</i> species accounted for 22.9% of the total bacteria in the initial phase, whereas <i>Halomonas</i> accounted for 43.2% in the end phase. Hence, the gradually increased salinity appears to facilitate the dominance of halophilic microorganisms in the long-term operation of an AGS-based biological treatment system and the stable retention of AGS.

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