Source Apportionment Of Heavy Metals In Municipal Sewage Sludge And Ecological And Health Risk Assessment

With the rapid growth of economy,urbanization and living standard for residents,the municipal wastewater production has been increased quickly.Sewage sludge,which is generated during the process of treating municipal wastewater,is quickly increasing.In consequence,disposal of municipal sewage sludge has become an imminent environmental problem.As a kind of persistent refractory pollutant,heavy metals will accumulate and pose a threat to ecological and human health if it was entered into the environment.Heavy metals in sewage sludge have become the critical limit factor for it's landuse.This study collected 158 municipal wastewater treatment plants in Shanxi to analysis the recycling of wastewater and disposal of sewage sludge situation.According to the regional industry distribution,technology treatment of wastewater,production of wastewater,32 municipal wastewater treatment plants were collected which can represent other municipal wastewater treatment plants in Shanxi.Sewage sludge collected from 32 municipal wastewater treatment plants were determine the content of heavy metals Cu,Zn,As,Hg,Pb,Cr and Cd and characteristic of heavy metals spatial distribution were also analyzed.Igeo was used to determine the pollution of heavy metals in sewage sludge,Pearson correlation was used to analyze correlations between each heavy metal in sewage sludge.According to the principal component analysis,three principal components of the sources for heavy metals in sewage sludge were conducted.In combination the three components with correlation between heavy metals,pollution of heavy metals and the regional industry,the three components of heavy metals in sewage sludge can be interpreted.Integrated the pollution loading index,Nemerow's synthetic pollution index and Hakanson potential ecological risk index to identify the ecological risk of heavy metals in sewage sludge when it was used to land and explore the high potential ecological risk areas;Based on the USEPA human health risk assessment model,the non-carcinogenic risk and carcinogenic risk between adults and children were compared;According to the Monte-Carlo model,uncertainty assessment of human health risk was carried out to verify the reliability of the certainty health risk assessment conclusion.The conclusions suggested:(1)Level of treatment wastewater from municipal wastewater treatment plants in Shanxi was low,secondary treatment was the main way,the quality of effluent of wastewater was poor which limit the recycling ways of waste water and induced that the main way of recycling waste water was industry use,and the complementary way was landscape in Shanxi;the main method of disposal of sewage sludge were land use and landfilling,building materials utilization and incineration were small and only a small proportion of sludge is disposed of directly;and different regions in Shanxi used the different methods to dispose sewage sludge:landfilling was the main way in the north of Shanxi,land use was the main way in the middle of Shanxi,the proportion of building materials utilization was the biggest in the south of Shanxi and the proportion of disposing the sewage sludge directly was the greatest in the southeast of Shanxi;(2)according to the mean values of content of heavy metals in sewage sludge,heavy metals in sewage sludge can be sorted as Zn>Cu>Cr>Pb>As>Hg>Cd,and the mean vales of it respectively was 281.31 mg/kg,162.59 mg/kg,152.26 mg/kg,39.56 mg/kg,14.83 mg/kg,2.09 mg/kg and1.97 mg/kg,the content of Zn was the biggest and Cd was the least;compared the biggest content of heavy metals with?Control standards for pollutants in sludges from agriculture use?(GB 4284-84),the content of Cu was slightly larger than the standard value and Zn was 1.5 times of the standard values;compared with the?Discharge standard of pollutants for municipal wastewater treatment plant?(GB18918-2002),the contents of all heavy metals were below the standard values.Compared with the national standards from developed countries,it is basically in the standard range.On the whole,the content of heavy metals in sewage sludge in Shanxi were basically within the standard which formulated by China and other countries in the world.(3)according to the results of Igeo,the pollution level of Cu and Hg were most serious,pollution of Cd and Cr take the second place and pollution of Zn,As and Pb were the lightest.According to the Pearson correlation analysis,significant correlations were found between Cu and Hg,Cu and Pb,Hg and Pb,meanwhile Zn and As,Zn and Cd,As and Cd also had significant correlation between each other,this suggested that those heavy metals which had significant correlations might have the same pollutant sources;In combination with the pollution of heavy metals,correlation between each metal and the regional industry in different areas,the three main components can be interpreted as:factor 1 can be considered as metallurgy,coking industry and traffic sources,induced the polluting of Cu,Hg and Pb,accounting for 35.7%;factor 2 can be defined as household wastewater and water supply system sources,induced the pollution of Zn,As and Cd,accounting for 29.04%;factor 3 can be considered as special industry source as leather tanning industry,textile manufacturing and chemical engineering,induced the polluting of Cr,accounting for 16.18%;(4)Pollution loading index suggested that pollution of Cu,Hg and Cd were heavily,Zn,As,Pb and Cr were moderately,and 87.5%of the sampling sites were unpolluted or moderately polluted;the Nemerow's synthetic pollution index showed that pollution of Cu,Zn,Hg and Cd were higher than other heavy metals.As and Pb were unpolluted in all samples,and the pollution of heavy metals in sewage sludge were not heavily as Pollution loading index suggested;according to Hakanson potential ecological risk index,the ecological risk of Hg and Cd were the highest,As,Pb and Cr were the leastest,and Cu and Zn were in the middle.Comprehensively all samples had high ecological risk when sewage sludge was used for land Synthesize the three ecological risk assessment indexes,pollution of heavy metals in sewage sludge were not heavily,but Cu,Hg and Cd should be pay more attention when sewage sludge were used for land;(5)according to the USEPA health risk assessment of heavy metals in sewage sludge,the average daily dose of Cu,Zn,Hg,Pb and Cr which were classified as non-carcinogenic pollutant for children was 8.75 times higher than that for adults,As and Cd which were classified as carcinogenic pollutant for children was 1.75 times higher than that for adults,and the main pathway of human exposure to non-carcinogenic and carcinogenic heavy metals were all ingestion.When adults/children exposed to one kind of non-carcinogenic heavy metals,the hazard quotient were all below 1,it depicted that in this case adults/children didn't have non-carcinogenic risk but the risk of children were higher than that of adults.When adults/children exposed to all kinds of non-carcinogenic heavy metals,adults didn't have non-carcinogenic risk but children had,and the main pathway of this risk was ingestion.When adults/children exposed to one kind of carcinogenic heavy metals,The index of Risk were all between 1×10-6 to 1×10-4,this risk can be accepted and in this case the risk of children were higher than that for adults.When adults/children exposed to the two kinds of carcinogenic heavy metals,the risk of adults/children were all below the limit value of 1×10-4,this depicted that the carcinogenic risk for adults/children was not significant,but the risk for children was 1.75 times than that for adults;The results of uncertainty health risk assessment were consistent with certainty health risk assessment,this suggested that the results of certainty health risk assessment were reliable.