Drainage network, especially in the old city, due to the difficulty of daily maintenance, pipeline deposition is widespread and serious. The existence of pipeline sediments will bring the following problems: reduce the capacity of the drainage pipeline and increase the hydraulic resistance of the drainage pipeline; when the overflow of the drainage system occurs in rainy days, the sediment will overflow into the receiving water body, causing water pollution and sulfur Organic matter fermentation produces hydrogen sulfide, which affects the safety of pipeline workers' downhole operations. Hydrogen sulfide can be converted into sulfuric acid by microbial action and corrode pipelines. However, there are few studies on the properties of sediments. The content of heavy metals and the risk assessment of the impact of heavy metals on the environment have been carried out. Studies on the nature of pipeline sediments in different functional areas have not yet been reported.
This article takes the old urban area of ​​city c, an important industrial city in the center of the Yangtze River Delta, as an example. The drainage pipe network in this urban area was built earlier, and the deposition in the drainage pipe is more serious. The focus of the research is to investigate the nature of pipeline sediments in different functional areas, so as to provide corresponding scientific basis for the planning and management of urban pipeline networks.
1 Sampling li sampling point function area selection In this study, four typical function areas of schools, living quarters, service areas and squares were selected from various function areas in the old city of c city as the sampling area.
Water supply and drainage water station 3/3 days / Ni 1.2 Sample collection and analysis 300 500g of pipeline sediment was collected from the inspection wells in each functional area and packed in sample bags. After removing the larger stone bricks in the sediments, they should be stored at a low temperature of 20 ° C and analyzed in time.
The particle size distribution was first wet-processed through a 20-mesh sieve and then measured with Dandong Baxter BT-9300S laser particle size analyzer. The density is determined by the pycnometer method. Total solid mass (Totalsediment, TS) is measured by baking at 103 ° to constant weight, and the mass of the deposit burned to constant weight at 600 ° in a muffle furnace is the non-volatile solid mass (NVS) , The volatile solid mass (VS, volatilesediment) is the difference between TS and NVS. The determination of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) uses the corresponding rapid determination reagents of Qingshijie Company. Heavy metals were analyzed by graphite furnace and atomic absorption spectrometer.
2 Test results and discussion 2.1 Basic properties of pipeline sediments in different functional areas (see Table 1) Table 1 Characteristics of sediments in different functional areas Pipe type density particle size distribution / on volume average ratio table Functional area average particle size area Rainwater Plaza Sewage Living Rainwater District From the VS / TS of the sediments in the functional areas of Table 1, it can be seen that the proportion of organic matter in the sediments of the pipelines in different functional areas differs significantly: square school> living quarters> service area. Through linear characterization, the density is obtained (the relationship between the ratio of inorganic matter NVS / TS (7) is: /o=8.=8), indicating that the density of the deposit is positively related to the relative content of inorganic matter, and the increase of the inorganic matter composition Can increase the density of sediments, which in turn will improve the sedimentation of particles. It can be seen from Table 1 that the pipe sediment D5 in each functional area is 12.3833.00pm. Except for the square, the particle size of the rainwater pipe sediment is smaller than that of the sewage pipe sediment. There is a slight difference in the particle size distribution of the sediments between the functional areas, and the sediment size of the pipe network in the living quarters is large, and there is no significant pattern as a whole.
Different pipeline functions affect the type of pipeline sediments. The sediments in the rainwater pipeline mainly come from the erosion of the underlying surface of the rainwater and atmospheric dust. Its organic content is relatively lower than that of the sewage pipeline. The VS / TS ratio is 0.1. The density of the material is large; the sediment in the sewage pipeline mainly comes from small-size residues of human excreta or kitchen garbage, and the organic content is relatively high. The VS / TS ratio is 0.050520190, generally greater than 0.1, and the density is small.
2.2 The content of conventional pollutants in pipeline sediments of different functional areas See the content of conventional pollutants in pipeline sediments of different functional areas. It can be seen that the contents of various conventional pollutants in sewage pipe sediments are as follows: school> living area> service area> square, and the pollutant contents in rainwater pipe sediments are all smaller than those in sewage pipe sediments. The pollutant content in the rainwater pipe sediments of each functional area differs little, while the pollutant content in the sewage pipe sediments differs significantly. COD in pipeline sediments in different functional areas: TN: TP rainwater sewage pipe service area school living area functional area aCODcr functional area square service area school living area functional area cTN pollutant content in sediments of different functional areas (hereinafter referred to as C: N: P) See Table 2. From Table 2, it can be seen that, except for the rainwater pipe sediment in the service area, the N / P value of the sediment is 1: (3.84.7), and the rainwater pipe in the service area is slightly smaller, at 1: 12.7 These results indicate that different functional areas have an important influence on the pollutant composition of pipeline sediments.
Table 2 C: N: P of pipeline sediments in different functional areas: P type of pipe in the living quarters of the functional area, rainwater pipe, sewage pipe, rainwater pipe and sewage pipe C: N: P30 1: For sewage pipeline sediments, the Cu, Cd, Cr and Zn content in the service area pipeline is the highest, the Pb content in the residential area pipeline is the highest, and the heavy metal content in the square pipeline is the lowest except for Cd. For rainwater pipeline sediments, the Cu, Cd, Pb, and Zn content in the pipelines in the residential area is the highest, the Cd content in the pipelines in the service area is the highest, and the heavy metal content in the pipelines in the square is the lowest. Overall, the Cu and Zn contents in the service area are relatively high. The levels of heavy metals in each functional area are: service area> living area> school> square.
The C / N of sewage pipeline sediments in service areas (including vegetable markets, fruit shops, restaurants and daily necessities stores) and living quarters is relatively high, which is likely to be related to the source of sediments mainly from kitchen waste. The sediment in the school sewage pipeline mainly comes from the toilet septic tank, and the nitrogen content is relatively high, so the C / N is low. The rainwater pipes in the service area not only contain the rainwater in the area, but also include the rinse water of the vegetable farm and the spilled kitchen fluid. These conditions have led to the highest relative content of sediment C in the rainwater pipe in the service area.
The rainwater pipe deposits in the square are mainly formed by rainwater washing the square. The relative content of organic matter is the lowest, so the C / N is the lowest. The sewage from the square comes from the underground mall of the square. The organic matter is relatively small, so the C / N is the lowest in all sewage pipeline sediments. The situation of the school is somewhere in between. Relatively speaking, the pollutant content of the rainwater pipe sediments in the service area is relatively high, and the rainwater scouring the pipes during rainy days is likely to cause higher pollution to nearby water bodies, so priority should be given to control.
The research of Ristenpart et al. Showed that the CODb content in the combined pipeline sediment is 42.69g / kg wet sediment, and the water content is 27.5%, which is equivalent to 58.88mg / g dry sediment. The research results are consistent with the rainwater pipeline sediment obtained in this paper The content of CODb in the material is equivalent. Because the rainwater pipes in the old city have mixed sewage pipes of different degrees, the water quality and the nature of sediments tend to be combined. In the study of esVollertsen et al., it was found that the CODb content of the sewage pipeline sediment was 214.1g / kg wet sediment, and the water content was 25.9%, which was equivalent to 288.8mg / g dry sediment, which was the same as the sewage pipeline deposition in this article except the square CODb content is equivalent. This shows that the CODb content of the same type of pipeline in different countries or regions is relatively close.
3 Heavy metal content in pipeline sediments of different functional areas See the heavy metal content in pipeline sediments of different functional areas. As can be seen from the figure, the nature of the functional area has a greater impact on the heavy metal content.
Square Service Area School Life Community Function Area a Square Service Area School Life Community Function Area cCd Square Service Area School Life Community Function Area bCu Square Service Area School Life Community Function Area dPb C â–¡ Rainwater El Sewage Plaza Service Area School Life Community Function Area e The content of heavy metals in sediments of different functional areas Li Haiyan and others investigated the content of heavy metals in the sediments of rainwater pipelines in several service areas in Beijing. Close to the outside, the average heavy metal content of other heavy metals differs greatly. The average heavy metal content of rainwater pipeline sediments in city C is significantly lower than that in Beijing.
It shows that the heavy metal content levels of the rainwater pipeline sediments in different regions may vary greatly.
Table 3 Comparison of heavy metal content of rainwater pipeline sediments in Beijing and C. The linear correlation coefficient i2 of different types of heavy metal content in rainwater pipeline sediment and sewage pipeline sediment is shown in Table 4. .
Table 4 shows that the correlation between Zn and various other heavy metals is strong, and it can be used as a representative index for evaluating the heavy metal content in pipeline sediments. Zhu Wei and others also believe that Zn can be used as a heavy metal characteristic pollution element in functional areas such as residential areas.
Table 4 Linear correlation coefficient of heavy metal content in sediment furnace (= 4> Heavy metal Note: 7 "The front and rear values ​​represent the data of rainwater pipes and sewage pipes, respectively.
3 Conclusions and recommendations The proportion of sediment inorganic matter is significantly related to the type of service area and the type of pipeline function. The proportion of organic matter in the sediment: the difference in the content of conventional pollutants in the sewage pipe sediment of each functional area of ​​the square is large: school> living area> service area > Square, rainwater pipe sediment rule is not obvious. The conventional pollutant content of the rainwater pipe sediment in the service area is relatively high, and the rainwater scouring the pipe during rainy days is likely to cause pollution to nearby water bodies and should be given priority control.
The pollution levels of heavy metals in each functional area are: service area> living area> school> square. The heavy metal content of pipeline sediments in service areas and living quarters is relatively high and should be paid attention to. The content of Zn in the sediment has a good correlation with the content of other heavy metals, which can be used as a representative indicator of the content of heavy metals in pipeline sediments.
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