Study On Comparation Of Environmental Impacts Of Typical Residual Sludge Treatment And Disposal Methods Based On Life Cycle Assessment

The treatment and disposal of residual sludge in sewage treatment plants has became an important problem for the sewage treatment industry.The present methods have different level of negative effects on the environment.This paper established an evaluation model based on the life cycle assessment method.Three common residual sludge disposal methods of sanitary landfill,aerobic composting and incineration were comprehensively and systematically evaluated by this method,in order to provide scientific basis for administrative decisions and environment sustainable development.The life cycle assessment model of this paper mainly includes processes as follow.According to the general process of residual sludge disposal,the environmental negative effects are divided into global warming,acidification,eutrophication,photochemical ozone,ecotoxicity,solid waste,soot and ash.Then the standardization and weighting calculations are conducted.Finally,the impact index for each of the remaining sludge disposal methods are quantified.On this basis,two typical sewage plants in the north and south of China:Xi'an No.3 Sewage Treatment Plant and Hefei Wangtang Sewage Treatment Plant are selected,respectively.According to the sludge composition,the three sludge disposal methods of sanitary landfill,aerobic composting and incineration were classified,weighted,and normalized based on the evaluation model.The pollutants discharge list in the process was obtained and the results are as follows:1.The order of environmental impact potential of different disposal methods are:sanitary landfill>incineration>high-temperature composting.As sanitary landfills generate a large amount of biochemical gas and the residual sludge is regarded as solid waste,the environmental impact potential of sanitary landfill is the largest.The high-temperature composting is considered to bring fertilizer instead of solid waste,the environmental impact potential for that is the smallest.2.For sanitary landfill,the order of environmental impact potential of various indicators is:solid waste>photochemical ozone synthesis>global warming>soot>acidification>eutrophication>ecotoxicity.Because of the large quality of landfill sludge and the occupation of large area,the environmental impact potential of solid waste is the highest.For the landfill process,the amount of biochemical gas generation is large,and the methane emission is the largest,which has a large environmental impact on photochemical ozone synthesis and global warming.3.In high temperature composting,the order of environmental impact of different indicators is:eutrophication>acidification>photochemical ozone synthesis>global warming>soot>ecotoxicity>solid waste.Because after the high-temperature composting process,the stock can be used as fertilizer for agriculture and almost no solid waste is generated.The environmental impact of composting is small.However,high-temperature composting generated large amount of NH₃,which is the main reason for high eutrophication.4.In the incineration treatment,the order of environmental impact of various indicators is:solid waste>photochemical ozone synthesis>soot>acidification>eutrophication>global warming>ecotoxicity.The sludge is incinerated and a large amount of ash was produced,which makes that the solid waste the largest environmental impact.In the process of incineration,the large amount of NO_X emissions is the main reason for the higher photochemical ozone synthesis.