Pilot Study on Start-up and Stable Operation at Low Temperature Based on Denitrifying Phosphorus Removal

Abstract

In order to understand the denitrifying and phosphorus removal characteristics of denitrifying phosphate-accumulating organisms (DPAOs), a pilot scale (20 m3) denitrifying and phosphorus removal experiment was carried out using a modified University of Cape Town (UCT) process at low temperatures of (6-16)℃. The test results show that at such temperatures, the hydraulic retention time (HRT) is 20 h and the solids retention time (SRT) is 35 days, and the modified UCT process can start up successfully and run steadily. When running steadily, the system can maintain nitrogen and phosphorus removal rates of 60%±5% and 80%±5%, respectively. The effluent concentrations of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) were 20, 5, 11, and 0.5 mg·L-1, respectively, which meet the first A emission standard of "Pollutant Discharge Standard for Urban Sewage Treatment Plant" (GB 18918-2002). In order to further investigate the characteristics of nitrogen and phosphorus removal in the system, the reflux ratio from the aerobic tank to the anoxic tank was increased to 150%. After the system was stabilized, it obtained higher nitrogen and phosphorus removal rates of 80%±10% and 90%±5%, respectively. Among them, denitrifying phosphorus removal in the anoxic tank accounted for 80%±4% of the total biological phosphorus removal. The average effluent concentrations of COD, NH4+-N, TN, and TP were 19.55, 0.1, 7.8, and 0.15 mg·L-1, respectively, which meet the Beijing Standard A discharge standard.