Journal of Hebei University of Science and Technology (Dec 2017)
Investigation on the pollution of road rainwater runoff in Shijiazhuang City
Abstract
To protect groundwater and urban ecological environment, much more sponge cities have been built in China. The sponge road is an important part of a sponge city. In recent years, Shijiazhuang Municipal Design Institute proposes a new sponge road structure, namely planting soil and crushed stone green belt, and it has been extensively used in Shijiazhuang City. In the design of the road structure, it is a key issue whether the infiltration rainwater quality pollutes the groundwater. Therefore, it is necessary to investigate the pollution of road rainwater runoff in Shijiazhuang City for the design of sponge road and the construction of sponge city. To obtain the characteristics of rainwater runoff pollution in Shijiazhuang City, four investigation points are chosen at the intersection of the Nanerhuan Road and Yuxiang Street, the east gate of Hebei University of Science and Technology, the site under the Xierhuan Road and Zhongshan Road overpass, and the catch-basin along the roadside in Shijiazhuang City. The investigating points are located in the main road of Shijiazhuang urban area, which covers Shijiazhuang City, and can represent the pollution characteristics of road runoff in Shijiazhuang City. Six rainfalls are collected from March to June in 2017. The rainfall on 3, May is viewed as typical middle and light one which is studied in this paper. The concentration of COD, TP, TN, NH3-N and SS in road runoff is tested by potassium dichromate method, ammonium molybdate spectrophotometry, potassium persulfate digestion-UV spectrophotometry and Nessler’s reagent spectrophotometry and filter paper filtration, respectively. The concentrations of Zn ions and Pb ions are tested by inductively coupled plasma method. According to the test results, the concentration evolutions of COD, TP, TN, NH3-N, SS, Zn and Pb ion in runoff during rainfall are studied. The results show that the contaminant concentration approximately decreases during the rainfall, and then maintain stable for 90 min. The relation between contaminant concentration and rainfall time follows the form of negative exponential function. Based on the investigation results, the design values of pollutant concentrations at the initial runoff and the long runoff of rainwater in Shijiazhuang are proposed by time-weighted average method and rainfall-weighted average method, respectively. The recommended values by former method for initial runoff in Shijiazhuang are as follows: TN, NH3-N, TP, SS and COD are 14.49 mg/L, 10.93 mg/L, 0.45 mg/L, 651.00 mg/L and 437.73 mg/L. The recommended values by former method for long runoff of water in Shijiazhuang are as follows: in 90 min TN, NH3-N, TP, SS and COD are 8.05 mg/L, 5.60 mg/L, 0.59 mg/L, 559.22 mg/L, and 237.96 mg/L, respectively. After 90 min they are 5.13 mg/L, 4.11 mg/L, 0.58 mg/L, 422.67 mg/L and 97.35 mg/L. The recommended values by later method for initial runoff in Shijiazhuang are as follows: TN, NH3-N, TP, SS and COD are 14.40 mg/L, 10.86 mg/L, 0.50 mg/L, 684.10 mg/L and 440.08 mg/L. The recommended values by later method for long runoff of water in Shijiazhuang are as follows: in 90 min TN, NH3-N, TP, SS and COD are 12.46 mg/L, 9.19 mg/L, 0. 52 mg/L, 642.80 mg/L and 363.92 mg/L. After 90 min they are 5.13 mg/L, 4.11 mg/L, 0.58 mg/L, 423.30 mg/L and 97.35 mg/L. Overall the proposed concentration values by the rainfall weighted average method are slightly larger than those by the time weighted average method. For hardly degradable Zn and Pb ions in the soil, the 30 min time-weighted concentration at the initial runoff and the long runoff of rainwater is proposed as the design values of runoff rainwater. The recommended design values of Zn and Pb ions are 0.67 mg/L and 0.11 mg/L, respectively.
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