Design And Efficiency Analysis Of Upgrading And Reconstruction Project Of A Sewage Treatment Plant In Shenyang City

With the acceleration of urbanization,the problem of water pollution is getting more and more attention.The government's improved standard on the receiving water quality of the surface also causes that the main sewage source-sewage treatment plant faces the problem of upgrading and reconstruction.A large number of sewage treatment plants nationwide are required to achieve the Standard A of the first class in "Discharge standard of pollutants for municipal wastewater treatment plant"?GB18918-2002?,which requires the sewage treatment plant to have higher removal capacity of COD,BOD₅,NH₃-N,TP and other pollutants rich in sewage,and gives higher requirements of the operation and management of sewage treatment plants.A sewage treatment plant in Shenyang is located in Shenbei New Area of Shenyang City,which adopts the A²/O two-stage biochemical treatment process.The construction scale of the first phase is 25,000m³/d and the final effluent is satisfactory with Standard A of the first class.According to the test data from July to December 2014,the average daily water treatment amount of the plant was21,000m³.When the cumulative frequency of influent quality was 90%,the measured COD,BOD₅,SS,NH₃-N,TN and TP concentration of the influent water was 258mg/L,113mg/L,236mg/L,29.2mg/L,36.88mg/L and 5.13mg/L respectively.Among them,the COD and BOD indicators were lower than the design values,and the other indicators were basically consistent with the design values.With the BOD₅/COD,BOD₅/TN and BOD₅/TP of the influent water was 0.44,2.93 and 21.2respectively,the sewage biodegradability was good and the biological removal effect of nitrogen and phosphorus could be guaranteed.The measured rates of reaching the Standard B of the effluent water on COD,BOD₅,SS,NH₃-N,TN and TP were 89%,100%,96%,100%,100%and 46%respectively.All indicators can meet the Standard A of the first class except TP,but they can't meet the Standard A of the first class.Therefore,in terms of the current situation of sewage treatment plant,the improvements of upgrading and reconstruction should be carried out and the advanced treatment unit should be added to ensure the effluent quality requirements after the secondary biochemical treatment.After the comparison of rationality,applicability and economic technology of many sewage advanced treatment processes,the process route of "coagulation,sedimentation+filtration" is selected from a variety of sewage advanced treatment processes.Finally,the processes of "coagulation+inclined-tube sedimentation tank+V-filter" and "high density sedimentation tank+fiber rotary disc filter" are selected,and further optimization,comparison and selection of the two processes above are carried out.This article uses the fuzzy matter-element analysis of Euclid approach degree combined with the method of expert scoring assignment in this paper.The advantages and disadvantages of two alternative processes are discriminated through designing 12 sub-goal levels,such as COD removal rate and BOD₅ removal rate,from three aspects of technical performance,economic costs and management effect.By comparing the Euclid approach degree values of the two alternative processes,the process of "high density sedimentation tank+fiber rotary disc filter" is closer to the ideal process for the advanced treatment process of sewage treatment plant.Then the parameters of this process are designed and calculated.The design scale of the renovation project is 25,000 m³/d.The project includes 1 new sewage lift pump pool,2 new high density sedimentation tanks divided into mechanical mixing zone,flocculation reaction zone and sedimentation zone,1 new filter room including fiber rotary disc filter and ultraviolet disinfection,and the total investment of construction project is 11.4382 million yuan.After its being put into operation,the dynamical monitoring of the water quality was carried out for nearly one year.In the case of COD 175⁷94mg/L,SS150²70mg/L,NH₃-N 17.5⁵5mg/L,BOD₅ 85¹20mg/L,TN 30⁶0mg/L and TP 4.4⁶.6 mg/L in the influent water,the fluctuation of the effluent indicators is small as the month changes,which meet the requirement of the Standard A of the first class.Among them,the removal effects of SS and TP are obvious,and the removal effects of ammonia nitrogen and TN are general.Through the operation of this advanced treatment system,the pollution discharges of the sewage treatment plant will be reduced greatly,which will contribute more to the comprehensive dredging of Liao River.