Abstract:

In this study,the sewage sludge samples were collected from ten typical sewage treatment plants of seven major cities in Guizhou Province from 2009 to 2012.The contents of heavy metals such as Cu,Zn,Pb,Cd,Ni,Cr,As,Hg were measured.The results showed that,in Guizhou Province,concentrations of Zn,Cd in sludge were higher than the control standard GB4284-84 (pH ≥65) and other heavy metals concentration in sludge were lower than the standard.Local manufactures and mining were found to exert impacts on heavy metals levels in sewage sludge in different plants.For example,in central region of Guiyang(S2),being affected by electroplating industries,the content of Zn,Cd,Cr in sewage sludge were much higher than those in other regions.In eastern region of Guizhou (S7),mercury mining leaded to an extremely higher concentration of Hg in regional sewage.The content of Pb,Cd of heavy metals in sewage sludge reached extreme value in western of Guizhou,where industry were dominated by leadzinc mining and coal mining.From 2009 to 2012,the rates of increase in As,Hg in sludge were 3622% and 8812 % respectively.It is probably because a large number of power plants had been built in recent years in Guizhou Province.Flue gas emissions could also result in As and Hg contamination in sludge.Except As and Hg,other heavy metals content in sludge didnt show obviously change during this 4 years.The Potential Ecological Risk Index (RI) and Nemerow Index (PN) were selected to assess the agricultural risk of using sewage sludge.The RI results showed that,in middle Guiyang (S2) and western Guizhou (S9),the RI index reached 4941 and 4270 respectively,suggesting an ecological risk of using sewage sludge for agriculture in these areas.Nemerow Index (PN) showed a same trend as RI.Therefore,these two kinds of sludge are not recommended for direct agricultural application to avoid environmental pollution.According to heavy metals content level and characteristics of sludge in different sewage treatment plant,sludge disposal measures should be reasonably selected