Risk Analysis Of Heavy Metals In Land Use And Disposal Of Municipal Sewage Treatment Plant Sludge

Centralized treatment of municipal domestic sewage is a common trend in the development of sewage treatment at home and abroad.The main by-product of centralized treatment of sewage is excess sludge,which contains a certain amount of heavy metals.It is not only difficult to degrade,but also has the characteristics of biological enrichment,which limits the utilization of excess sludge as a resource.Therefore,the environmental risk analysis of heavy metals utilization in excess sludge of municipal wastewater treatment plant can provide reference for the final disposal and comprehensive utilization of sludge,and is a hot issue of general concern in the industry.At present,the study of heavy metal environment in the process of sludge recycling is still not perfect,and the study of environmental risk assessment is not deep enough.In order to solve the above problems,the residual sludge of urban sewage treatment plants in Hebei Province was taken as the research object,and the heavy metal content of the residual sludge was investigated,land use risk assessment and resource disposal and utilization were carried out.Firstly,the contents of heavy metals such as Cu,Zn,Cr,Cd and Pb in sewage sludge of municipal wastewater treatment plants in Hebei Province were determined by atomic absorption spectrophotometry,and compared with the standard of agricultural mud utilization.Secondly,in view of the heavy metal content determined by analysis,single factor pollution index method,Nemerow pollution index method and geological cumulative pollution index are used to analyze and judge the pollution grade of land use process,and then determine the pollution grade of Cu,Zn,Cr,Cd,Pb and five comprehensive pollution grades of various heavy metals.Finally,the toxicity of heavy metal leachate was studied for sludge with high risk of heavy metal pollution and unsuitable for land use,and the specific ways of resource utilization were put forward.The contents of heavy metals such as Cu,Zn,Cr and Pb in sludge of every plant in Hebei Province are relatively low,but only Cd content is relatively high.The Cd content in 80% of sludge samples exceeds the standard limit of grade A agricultural mud utilization for sludge disposal in municipal sewage treatment plants.The results of comprehensive single factor pollution index method,geological cumulative index method and Nemerow comprehensive pollution index method showed that 89 sewage treatment plants had low risk of heavy metal pollution in land use(agricultural)and could be used in agriculture or forestry;29 sewage treatment plants had high risk of heavy metal pollution and were not suitable for land use,but their concentration of heavy metal leachate was in line with that of other sewage treatment plants.Relevant standards can be disposed of by utilizing building materials,making ceramsite and burning heat energy.