Impact Of Effluent From A Sewage Treatment Plant In Shanghai On Water Quality Of The Yangtze River Estuary In The Receiving Area

Yangtze River Economic Belt is the inland economic zone with a global influence,and the Party Central Committee and the State Council attached great importance to environmental protection of the Yangtze River Economic Belt.President Xi has made important instructions on ecological environmental protection and restoration of the Yangtze River Economic Belt on many occasions.President Xi emphasized"together with the great protection of the Yangtze River and not engage in large-scale development",and listed the"Yangtze River Protection and Restoration"as one of the iconic battles for pollution prevention and control.At the same time,he required that the"lucid waters,lush mountains,and invaluable assets"be handled properly,the establishment of ecological forbidden areas,and comprehensively do a good job of ecological environment restoration of the Yangtze River.The Yangtze River Estuary is the outlet of the Yangtze River and is one of the key areas for ecological protection of the Yangtze River.There are a total of 29 sewage outlets around the Yangtze River Estuary along the river?referring to a daily drainage volume of 300m³ or an annual drainage volume of 100,000m³ and above?.The water environment capacity of the Yangtze River Estuary is not infinite,and a large amount of effluent will seriously affect its water quality after entering the Yangtze River Estuary.The effluent from a Shanghai sewage treatment plant studied in this paper is discharged to the Yangtze River Estuary.The effluent of a sewage treatment plant in Shanghai after being upgraded is still discharged to the Yangtze River Estuary.Therefore,the effluent of the sewage treatment plant and the receiving area of the Yangtze Estuary are taken as the research object to study the influence of the effluent of the sewage treatment plant on the chemical and biological indicators of the Yangtze River Estuary.The chemical indicators of the Yangtze River Estuary include basic control items?COD,BOD₅,NH₃-H,TN,TP,Petroleum?,first-class pollutants(Hg,Cd,Cr⁶⁺,As,Pb),and select control items?Ni,Cu,Zn,Cyanide,Sulfide,Volatile phenol?,a total of 17pollutants,and 16 types of PAHs that are preferentially controlled by USEPA;and biological indicators include zooplankton,phytoplankton and benthic animals.Based on the investigation of the chemical and biological indicators of the Yangtze River Estuary before the upgrading of the sewage treatment plant,a comprehensive study of the influence of the effluent after the sewage treatment plant's upgrading on the water quality of the Yangtze River Estuary has been concluded as follows:?1?In the receiving waters of the Yangtze River Estuary,except for TN,Petroleum,Hg,and Volatile phenols,other indicators in the basic control projects,first-class pollutants,and selective control projects meet Class II standards.Compared with the water quality of the affected area of the Yangtze River Estuary before the upgrading of the sewage treatment plant in year 2015,the water quality has generally improved,but the indicators of Hg and Volatile phenols have still deteriorated.According to analysis,these may be mainly related to various comprehensive factors such as illegal dumping of garbage,ship transportation,landfill leachate,and wastewater discharge from chemical parks around the Yangtze River Estuary.Only effluent discharge from sewage treatment plants is not enough to cause pollution to the water quality of the Yangtze Estuary.The concentration of PAHs in the water and sediments of the Yangtze River Estuary is significantly lower than the previous survey results.At the same time,the concentration of PAHs in the effluent of the sewage treatment plant is lower than that of the stations in the Yangtze River Estuary,and the types of monomer PAHs detected are also significantly less than those detected in the Yangtze River Estuary.Further source analysis indicates that the pollution of water and sediments in the Yangtze River Estuary comes from the combustion of grass,wood and coal,and the PAHs in the effluent of the sewage treatment plant come from petroleum combustion.Significant differences in concentration and composition of PAHs from the effluent of the sewage treatment plant and the Yangtze River Estuary,and the source analysis indicates that the sources are different.Therefore,the effluent from the sewage treatment plant will not cause pollution of the chemical indicators of the Yangtze River Estuary.?2?A total of 62 species of 4 types of zooplankton were identified in the Yangtze River Estuary in year 2019,including 19 species of copepods,14 species of branch horns,13 species of rotifers,16 species of protozoa.The abundance ranged from173.75 to 485.25 ind./m³,and the biomass is 11.71?62.75 mg/m³.There are 7dominant species,and the most dominant nauplii is 0.18.The Shannon-Weaver index is between 1.46?1.72,Margalef index is between 1.02?1.29,and Pielou uniformity is between 0.55 and 0.68.Compared with the results in year 2014,zooplankton species increased slightly,abundance and biomass decreased,while the biodiversity index was basically the same.A total of 6 phytoplankton species were identified,including 27 species of cyanophyta,22 species of chlorella,35 species of diatom,6 species of euglenophyta,1 species of chrysophyta,and 4 species of rhodophyta.The abundance range is 297.44 dominant species,and the most dominant microcystis spp.is 0.11.The Shannon-Weaver index is between 0.51?1.28,the Margalef index is between 0.40 and0.84,and the Pielou uniformity is between 0.27 and 0.54.Compared with the year2014 survey results,the number of species and dominant species are significantly lower than the survey,while the abundance and biomass are slightly higher than the survey,and the biodiversity index is basically the same as the survey.A total of 17 species of 3 benthic organisms were identified,including 6 species of phyla,8 species of arthropods,and 3 species of molluscs.The abundance is14.00?382.25ind./m²,and the biomass is 0.10?22.61g/m³.The Goodnight-Whitley biological index is 4.83%.The number of benthic species surveyed in year 2014 is less than that in year 2019,and the abundance and biomass are basically the same,but the Goodnight-Whitley biological index is much larger than 4.83%this time.From the study of phytoplankton,phytoplankton and benthic animals,the effluent from the sewage treatment plant did not adverse affect its community structure,and from the indication of the zooplankton,phytoplankton and benthic animals on the water environment,the water quality of the Yangtze River Estuary in this survey has improved compared with previous studies.