Effects of On-stream Detention Pond on Polluted Urban River Purification

To analyze the purifying effect of on-stream detention pond (OSDP) on polluted urban river in high temperature period (18-30 ℃), medithermal period (9-25 ℃) and hypothermic phase (5-17 ℃), three kinds of on-stream detention ponds were adopted and monitored. The retention time (HRT) of OSDP-A with a narrow channel and a fast flowing rate is 0.5 d, the HRT of OSDP-B with a wide channel and a slow flowing rate is about 2 d, the HRT of OSDP-C possessing a bank wetland and fast flowing rate is about 0.3 d. Under different temperature conditions, the removal efficiency on different pollutants indexes of 3 kinds of natural OSDPs was compared. The results shown that in the OSDP-A, the removal efficiency of TN can reached the highest, about 12%. The OSDP-B presented the best removal capability for TP with its removal efficiency as much as 45%. However, the highest removal efficiencies of COD_Cr were observed in OSDP-C, being 37%. The effects of various kinds of OSDP on the removal of nitrogen, phosphorus and organic contamination were observed, and the removal rates of TP and COD_Cr were better than TN in general. Additionally, with water temperature increasing, the treat capability of different OSDPs kept relative stable; while with water temperature decreasing, their removal efficiencies presented unstable.