Research On Risk Assessment Of Urban Sewage Pipeline And Optimal Operation Of Sewage Pumping Station

The urban sewage treatment system includes three parts: sewage pipeline,sewage pumping station and sewage treatment plant.Sewage pipeline undertakes the task of collecting and transferring sewage as well as some natural precipitation.Sewage pumping station guarantees that sewage can be transported to sewage treatment plants.Presently,due to the difficulties in transforming the combined sewerage system into separated sewerage system,the combined sewage pipeline still accounts for a large proportion in the old city.These pipelines are unreliable for their old ages and low design standards.And as part of the sewage treatment system,the sewage pumping station has the characteristics of high energy consumption,non-uniformity of the inlet and outlet water,which needs to be optimized urgently.In view of these problems,this paper studies the risk assessment of the combined sewage pipeline and the optimal operation of the sewage pumping station.(1)Risk assessment of combined sewage pipelineThis paper makes a comprehensive analysis of the risks existing in combined sewage pipeline.There are four risks involved in the combined sewage pipeline:methane explosion risk,hydrogen sulfide poisoning risk,overflow pollution risk and environmental risk,and the impact of these risks are analyzed.The Analytic Hierarchy Process(AHP)is used to construct the hierarchical analysis structure and to establish the risk assessment model.After that,the risk assessment index and grading criteria of the combined sewage pipeline are determined by using the Grey Relational Analysis(GRA)to calculate.Choosing 4 sections of combined sewage pipeline in Hefei City for risk assessment,it is concluded that pipeline 2 is in a safe state,pipeline 1 and 3 are in a relatively safe state,while pipeline 4 generally safe.The evaluation result is relatively accurate.(2)Research on optimal operation of sewage pumping stationAfter analyzing the basic idea of sewage pumping station optimization,the objective of optimization is to minimize the variation of pumping station outflow under the condition of guaranteeing regional storage capacity.On this basis,the number of start-up and shut-down times is optimized,and the flow distribution among units is carried out to achieve the minimum energy consumption under this condition.With the constraints of the volume of collecting pool,flow and head of pumping station,the optimal operation model of sewage pumping station is established.Solving the problemby genetic algorithm(GA).Finally,the Xinghua Pumping Station in Hefei City is selected as an example to calculate.The results show that if the volume of the collecting pool increases by 10 times,the discharge of the pumping station is roughly divided into two steady outflow stages.Under this condition,the start-up and shut-down of the pumping unit is twice,saving annual operating costs of 64,000 yuan;When the volume of the collecting pool of the pumping station expands 22 times,the pumping station can achieve steady outflow,the start-up and shut-down of the pumping unit is zero.Under this condition,the annual operating cost is saved 91,900 yuan.The optimization method has considerable economic benefits.