To explore the influence of the influent flow distribution ratio on the denitrification efficiency of low-temperature urban wastewater and analyze the denitrification of multi-level AO coupled flow biochemical process, three-level AO-coupled biofilm technology was used to treat simulated low-C/N urban sewage at a temperature of 10℃±1℃, hydraulic retention time of 8 h, and constant air-water ratio. The reactors were operated under three conditions of inlet water ratios of 5:4:4 (equal volume load), 3:2:1 (equal hydraulic retention time), and 25:15:6 (equal sludge load). The study showed that the multi-level AO-coupled displacement biochemical process has a good removal efficiency with respect to low-temperature and low-C/N wastewater. The pollutant removal efficiency is the highest when the ratio of the influent is 3:2:1 and the average removal rates of COD, NH4+-N, and TN are 87.44%, 96.63%, and 76.81%, respectively. Further studies on the law of nitrogen migration and transformation showed that the main factors constraining the nitrogen removal under three conditions were the nitrification efficiency at each levels, the ratio of 3:2:1 influent reasonably distributing the influent load, and the nitrification efficiency at each level exceeding 85%, creating favorable conditions for denitrification and leading to a higher denitrification efficiency, while the system has the highest total biomass. The research results enrich the theory of multi-level AO cryogenic removal of nitrogen and provide references for engineering designs and applications.
Keywords: activated sludge; biofilm; biological denitrification; coupling process; low temperature.