| This paper aims to introduce our research findings on the each effect of the sediment accumulation, erosion release and biodegradation on organic matter removal under different flow in sewer network. In proceeding with our work, we have established simulated sewer networks systems with and without sediments and used the sewage and sediment in sewer as an experimental target, analysised and explored the different flow pipe wastewater quality change, physical and chemical characteristics of pollutants and suspended solids, At the same time, the particle size distribution in water and particle composition of inflow and effluent and characteristics of the graded composition were analyzed under different flow velocities as well.Finally, we have obtained the rules of the pollutant deposition and release to water quality change under different flow. Therefore the research provides a certain theoretical basis for water quality forecasting and sediment control management.Through the simulation reaction device, water quality variation was studied under different hydraulic conditions, the results showed that when the velocity was small, the removal rate of pollutants was a quite large, it has to do with the condition of microorganism and suspended particle deposition occurred more relevant under low velocity.With the increase of the flow velocity, pollutant removal rate decreases, and sediment release enhanced, at the same time, the effect of physical sedimentation and biological degradation was weak. In addition, by three-dimensional fluorescence and molecular weight analysis, we have studies the transformation characteristic of the water pollutants, the results showed that the water in the process of conveying tends gradually humification, and humus stems from microbial residues, and the processweakened the aromaticity of organic matter, reduced the benzene ring structure, in addition, sewage biodegradability was improved and sewage organic matter content which was utilization by microbial easily was increased.On the basis of research on water quality changes, the research applicationed windward's grade classification standards, analysised the pipeline suspended matter and sediment particle size distribution changes, different grade VS/TS, and nitrogen and phosphorus pollutants concentration distribution, the research results showed that under different flow velocity, the proportion of D < 4 microns of suspended particles was increasing and large particles constantly cut flush into small particles, For the sedimentation,D > 125 microns of suspended particles proportion was reduced, In addition, Particle diameter D < 63 microns contained the most organic matter, which was total more than 70% of the VSS, and coarse particles was mainly composed of inorganic pollutants.Based on the basic assumption of the first flush, pipe sediment pollution release model was established, Results showed that under the condition of 6h of hydraulic flow at velocity 0.32m/s, sedimentation, erosion release, biodegradation process contributed 55.6%, 14.6%, 28.8% of the organic matter variation in sewer respectively. When the flow rate increased to 0.6m/s which is a minimum sewer design flow, pollutant deposition phenomenon has been significantly improved but the release effect scour enhanced and biodegradation changed little. Variation of organic matter contributions from these three effects were 39.2%, 38.1%, 22.7% respectively. When the flow rate is further increased to 0.9m/s change, the contribution ratio of contaminants deposition was further reduced to 21.4%. Sedimentation effect significantly declined. However, erosion release became the major mechanism for organic matter variation, which is around 65.6%. At the same time, there was only weak biodegradation effect(13.1% contribution). |
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