Process And Influencing Factors Of Sewage Pipe Network Formation Of Deposits In Xi’an

This article has taken the sewer networks system of Xi’an as the object of the research, analyzed the factors which were related to the sedimentation and the scouring effect in the process of deposit formation. The main aspects have been analyzed, such as the thickness of sediment, particle size distribution, the condition of hydraulic and water quality, by using pipeline robot combined with sonar imaging technology.The results showed that the deposition phenomenon existed in 79.1% of the main sewer pipes of Xi’an, and it was easier to find sediments in the combined flow system than the separate flow system. The deposit formation was mainly related to the flow, velocity and particle size distribution of suspended solids of sewage. Generally speaking, the thickness of sediment showed an increasing trend along the flow direction. The study further pointed out that the sediment mainly consisted of inorganic particulate matter, and the component of organic matter was less than 20%. In the experimental data of particle size distribution of sediment, the propotion of silt(4μm<D<63μm) was highest, which remained in the range of 40%~60%; The propotion of grit(D>500μm)was lowest, which remained in the range of 0.5%~1%. Under the same hydraulic conditions, the small particle size matter which had less dense on the surface layer of sediment was easier washed.Further research results showed that sedimentation and erosion were the main factors influencing the formation of sediments. When the flow rate was low, the content of SS decreased gradually along the pipeline. This result showed that suspended matter was deposited in sewage pipeline. In the system of the main pipe, the deposition phenomenon was easier to existed in the local area of the confluence and inflection point. At the same time, with the angle of deposition point became large, sediment thickness change was more obvious. The metabolism of biofilm has affected the formation of sediment. The metabolites of microbes existed on biofilm and the loss of biofilm made a a certain degree of contribution on the formation of sediment.