Research on improving biological nutrient removal by a modified Pasveer oxidation ditch with additional internal anoxic zones
内置缺氧区的改良型Pasveer氧化沟工艺脱氮除磷性能研究

In order to solve the problem that carbon source could not be fully utilized by denitrifiers in anoxic zones of the Pasveer oxidation ditch (OD), a pilot-scale Pasveer OD modified with presence of additional internal anoxic zones was adopted to investigate the nutrient removal process through varying the internal recycle ratio in this study. The results showed that when the internal recycle ratio was 200%, the system obtained the highest nutrient removal efficiency. The effluent TN and TP contents were 12.7 mg/L and 0.34 mg/L, respectively, with the removal efficiencies remarkably improving to 61.9% and 89.2%. The results indicated that additional internal anoxic zones could optimize the utilization of avail carbon source from the anaerobic outflow for denitrification and stimulate denitrifying phosphorus removal process, which were both beneficial for biological nitrogen and phosphorus removal when treating wastewater with carbon source limited. However, the excess internal recycle would cause nitrite to accumulate in the aerobic zone, which seems to be harmful to biological phosphorus removal.