Nutrient removal by full-scale Bi-Bio-Selector for nitrogen and phosphorus removal process treating urban domestic sewage at low C/N ratio and low temperature conditions

Abstract

For solving the nutrient removal from urban domestic sewage at low temperature and low C/N ratio, the full-scale Bi-Bio-Selector for Nitrogen and Phosphorus removal (BBSNP) process was set in Shanghai, China and run continuously at C/N about 3.6. It was run for 133 days along with the temperature dropping from 22±2℃ to 10±2℃. After 27 days’ operation, the performance of BBSNP process reached to stable. Chemical oxygen demand (COD), NH4+-N, total nitrogen (TN) and total phosphorus (TP) in effluent were lower than 40, 0.5, 8 and 0.1mg/L, respectively. The NH4+-N and TN removal efficiency were influenced and decreased at low temperature (10±2℃). After improving mixed liquor suspended solids (MLSS) from 4000mg/L to 6000mg/L, the nitrogen removal efficiency lifted to previous level because of the increasing NH4+-N and NO2−-N oxidation rate of suspended sludge. Denitrifying phosphorus accumulating organisms (DPAOs) were the dominant bacteria responsible for phosphorous removal in this study. The Denitrifying phosphorus removal (DPR) efficiency was as high as 74.16±4.40%. Dechloromonas was in higher amount than other DPAOs in the BBSNP process. The results of this study provided a convincing evident that BBSNP could be a practical and cost-effective process for removing nutrient from urban domestic sewage.