Demonstration On The Process Scheme Of An Underground Sewage Treatment Plant In Tianjin

Tianjin is a city with serious water shortage.In recent years,water has been diverted from other places frequently,and the pollution of local water resources is serious.The construction of large-scale,high-standard and less-occupied underground sewage treatment plant is of great significance to the ecological environment of Tianjin.In order to solve the problem of process selection in underground sewage treatment plant,this paper firstly analysed the water quantity and quality of the original sewage treatment plant;and then demonstrated the process of each treatment unit according to the structural characteristics of underground box structure.Finally,through the comparison of technology and economy,the process scheme suitable for underground sewage treatment plant with high discharge standard was determined.The main results of the study were summarized as follows:The water inflow of the original sewage treatment plant with 90% guaranteed rate was 396,000 m3/d.Most of the influent water quality indexes of the original sewage treatment plant exceed the original design standards,and the average values of COD,BOD₅ and TN indexes exceed the "Water Quality Standard for Sewage Discharge into Urban Sewerage"?CJ343-2010?.The effluent quality could meet the original design of "Grade I B" standard,but it could not meet the local discharge standard of Tianjin,"Pollutant Discharge Standard of Urban Sewage Treatment Plant" A standard.Considering the present situation of the original sewage treatment plant and the overall requirement of the surrounding environment,the upgrading project adopted the form of underground sewage treatment plant,and its layout adopted the form of semiunderground double-deck capping.The design scale was 600,000 m3/d.The design effluent quality meeted the Tianjin local discharge standard,"Pollutant Discharge Standard of Urban Sewage Treatment Plant" A standard.The removal efficiency of each pollutant was as follows: COD ? 95.6%,BOD₅ ? 98.3%,SS ? 98.3%,ammonia nitrogen ? 97.0%?94.0%?,TN ? 87.5%,TP ? 96.7%.The BOD₅/COD value of the designed influent water quality of the proposed underground sewage treatment plant was 0.51,and the sewage was suitable for biological treatment.BOD₅/TN = 4.31,the carbon source of sewage was abundant.A reasonable arrangement of biological ponds was adopted to ensure the rational utilization of carbon source and the effective removal of total nitrogen.BOD₅/TP = 38.3,biological phosphorus removal combined with chemical phosphorus removal could be adopted,and the phosphorus removal effect was strengthened by the method.The overall process scheme of the proposed underground sewage treatment plant was determined as follows: multi-stage AO process + efficient sedimentation tank + deep bed filter + ozone oxidation process was selected for the sewage treatment process,and ultrafiltration + reverse osmosis process was selected for the regenerated water treatment process.The expected efficiency of the underground sewage treatment plant will be better than that of Jinggu sewage treatment plant with the similar process technology.The design process of the project is reasonable,and the effluent quality can meet the A standard of Tianjin local discharge standard?DB12/599-2015?.Taking a sewage treatment plant in Tianjin as an example,this paper concluded that some research results could provide technical reference for the design and construction of underground sewage treatment plants,and have certain guiding significance.