Study On Upgrading And Reconstruction Technology Of A Wastewater Treatment Plant In Liaoning

With the rapid development of economy and society,the water pollution problem is increasingly emphasized by people,which leads to that a majority of sewage treatment plants in China has an urgent need to solve the key problem of poor treatment effect and substandard quality of the produced water through the methods of standard improvement and modification.This subject takes the standard improvement and modification engineering of the sewage treatment plant in county A of Liaoning province as a study object.According to the results of the analysis on the variations of the inlet water and outlet water in water quality and water amount,it determines that the design scale of the modification engineering is 10000 m³/d,the designed inlet water quality of the secondary treatment process is that the COD content is 380mg/L,the BOD content is 200 mg/L,the NH₃-N content is 40 mg/L,the TN content is 50mg/L and the TP content is 5 mg/L,the designed outlet water quality of the secondary treatment process is that the COD content is 70 mg/L,the BOD content is 25 mg/L,the NH₃-N content is 8 mg/L,the TN content is 20 mg/L,and the TP content is 1 mg/L,and the designed outlet water quality of the constructed wetland reaches a grade-I standard A.It draws a conclusion that the the sewage treatment plant in county A has good biodegradability and can also meet the denitrification and phosphorus removal requirements.Through the comparative analysis on the expansion of the capacity of the existing A/O biochemical pools,multilevel A/O process,MBR process,BAF process and MBBR process,the modification scheme of the secondary treatment process is determined to be selected from the MBR process or the MBBR process.According to the results of the comparative analysis on three aspects of the two schemes,i.e.the modification scale,the advantages and disadvantages and the difficulty in operation and maintenance,the MBBR process is preferred as the modification scheme of the secondary treatment process.The overall Euclid approach degrees of the two schemes,i.e.the MBR process and the MBBR process obtained by using a fuzzy matter-element model are respectively 0.1692 and 0.6981,which is used as a basis to judge that the use of MBBR process as the modification scheme of the secondary treatment process is more reasonable.According to the results of comparative analysis on the two schemes,i.e.“horizontal subsurface flow constructed wetland plus surface flow constructed wetland”and“two-level horizontal subsurface flow constructed wetland”in the aspects of engineering investment,land occupation area,treatment effect and sanitation conditions,the two-level horizontal subsurface flow constructed wetland is determined as the modification scheme of the constructed wetland.This modification engineering will build one new two-level horizontal subsurface flow constructed wetland having an area of 18200 m²,and will build one lifting pump house having a design flow rate of 10000m³/d and will construct two sewage pipelines having a total length 1925 m.The hypoxic zone and aerobic zone of the modified A/O biochemical pool respectively have the capacity of 1951.43 m³and 4037.41 m^3.The filling rate of stuffing added in the middle section of the O section is 35%,and the stuffing is HDPE.The modified secondary treatment process is A/O-MBBR process,and the advanced treatment process is original high-efficiency chemical sedimentation tank+original fiber rotary filter+two-stage horizontal subsurface flow constructed wetland.The stable operation result of the sewage treatment plant in county A after the modification indicates that the average value of COD,BOD,NH₃-N,TN and TP in the outlet water can respective reach 17.1mg/L,6.2mg/L,2.3mg/L,6.4mg/L and 0.15mg/L,that is,the discharged water quality of various indexes can reach the grade-I standard A in the national standard“Discharge Standard of Pollutants in Municipal Wastewater Treatment Plant”（GB18918-2002）.