Evaluating the optimal oil concentrations in the startup performance of a membrane bioreactor treating oily noodle-soup wastewater

The discharge of high-strength oily wastewater adversely affects the environment; therefore, the treatment of wastewater containing fats, oils, and grease from the food industry is of importance. In this study, we used a membrane bioreactor (MBR) to treat Ramen noodle-soup wastewater, and we evaluated the optimal oil concentration in the wastewater for the startup of the MBR treatment in winter and summer. The MBR system had a sufficient startup in both seasons when fed with a 20-fold dilution of the original oily wastewater, containing approximately 950 to 1,200 mg/L oil and approximately 3,000 to 4,400 mg/L biological oxygen demand (BOD; BOD-SS load of 0.1 to 0.2 kg/kg/d). Activated sludge microbes were not highly active with a 40-fold dilution of wastewater, because of the decreased mixed liquor suspended solid concentration during the operation period. Population shifts in the sludge microbiome with increasing oil concentrations were analyzed using high-throughput sequencing, and the relative abundance of operational taxonomic units belonging to the phylum Bacteroidetes were highest in both winter and summer when fed with 20-fold dilution of the wastewater. In particular, the family Chitinophagaceae were dominant, with relative abundances of 13.5% in winter and 5.1% in summer, suggesting that these families may play important roles in the startup of a MBR treating the wastewater.