连续降雨条件下典型泵站放江污染特征分析

鉴于上海市中心城区地表径流采用强排模式,由泵站排入受纳河道,常引起河道阶段性黑臭。为明确泵站放江污染对受纳河道的影响程度,选取中心城区典型泵站,在连续降雨期间监测评估了泵站放江水质、水量及其对受纳河道的影响程度。结果表明,在水量上,受连续降雨与泵站运行模式影响,降雨4.5 mm时的累积放江水量达61 410 m~3,放江水量达到服务区理论径流量的近7倍。在水质上,五日生化需氧量(BOD_5)、高锰酸盐指数(COD_(Mn))、氨氮(NH_3-N)和悬浮物(SS)事件平均浓度分别为43.2 mg/L、35.3 mg/L、33.4 mg/L和75.0 mg/L,细菌总数(total bacteria, TB)和大肠菌群(total coliforms, TC)事件平均浓度为6.8×10~6CFU/mL和5.7×10~5CFU/mL。对受纳河段而言,放江期间河段流速在3 cm/s左右,泵站放江污染物不能快速有效地扩散迁移,污水团在河道形成表观区域性黑臭,在排污口20 m范围内,主要污染物BOD_5、COD_(Mn)、NH_3-N和SS平均浓度与泵站放江水质接近,分别为35.0 mg/L、28.7 mg/L、28.1 mg/L和100.9 mg/L;TB和TC平均浓度为3.6×10~6CFU/mL和3.4×10~5CFU/mL。受河网流速影响,泵站排放口上下游样点受泵站放江影响小,相比而言,主要污染物变化趋势不显著。为有效降低排水系统雨天放江污染负荷,保障受纳河道水质改善效果,提出了挖掘截流设施潜力、推进雨污混接改造及加大河道生态修复力度等措施。

Effects of Sewage Discharge from Drainage Pumping Station on Receiving River Water Quality Under the Condition of Continuous Rainfall

Eutrophication and black, foul smelling water are prevalent problems found in the urban water environment. Previous studies have shown that pumping station discharge was the main source of black water in medium and small rivers in Shanghai. The effect of water discharged from municipal pumping stations on receiving streams was investigated in a case study. The quality and quantity of water discharged from a typical pumping station, under conditions of continuous rainfall, were monitored and its influence on the receiving stream was analyzed. Water samples were collected at four sites: Site A0, 500m above the pumping station outfall; Site A, in the pumping station forebay; Site A1, 20m below the outfall; Site A2, 1000m below the outfall. Water samples were divided into two groups, one for determining water quality parameters (BOD5, CODMn, NH3-N and SS) and the other for determining microbiological indicators (TB and TC). Results show that the water volume discharged from the pumping station was seven times higher than the theoretical surface runoff. During the investigation, the rainfall was 4.5mm, and the cumulative discharge amount reached 61410 m3. The concentration of BOD5, CODMn, NH3-N, SS, TB and TC at the pumping station (Site A) were 43.2 mg/L mg/L, 35.3 mg/L, 33.4 mg/L, 75 mg/L, 6.8×106 CFU/mL and 5.7×105 CFU/mL, respectively. The flow velocity of the receiving river was approximately 3 cm/s, insufficient for pollutant dispersal, and the discharge led to formation of a black, foul smelling mass in the river. Within 20 meters of the sewage outfall (Site A1), the average concentrations of the main pollutants BOD5, CODMn, NH3-N , SS , TB and TC were very close to those at the pumping station (Site A), with values, respectively, of 35.0 mg/L, 28.7 mg/L, 28.1 mg/L, 100.9 mg/L, 3.6×106 CFU/mL and 3.4×105 CFU/mL. However, the pumping station discharge had little effect on water quality upstream (Site A0) and downstream (Site A2) of the pumping station. We recommend three actions to decrease pollution loading by pump station discharges and protect water quality in the receiving river: (1) Prevent and control illicit connections to the drainage system; (2) develop intercept facilities and a combined sewer system for conveyance of storm runoff and sewage; and (3) increase ecological restoration of river channels.