Distribution Characteristics of Typical Heavy Metals in Sludge from Wastewater Plants in Jiangsu Province (China) and Their Potential Risks

Recently, increasing attention has been paid to heavy metals in sludge. However, limited literature could be found on the distribution characteristics of heavy metals in sludge and their potential risks. In this study, sludges from wastewater plants in Jiangsu Province (China) were selected for the investigation of heavy metal loadings, showing that typical heavy metal levels were in the order of Zn > Cu > Cr > Ni > Pb > As > Hg > Cd, ranging from 154 to 2970 mg/kg, 28 to 1150 mg/kg, 10 to 136 mg/kg, 9 to 262 mg/kg, 0 to 79 mg/kg, 12.1 to 41.6 mg/kg, 0.67 to 19.50 mg/kg and 0.21 to 2.77 mg/kg, respectively. Analysis of the typical heavy metal distribution in sludge indicated that Hg, Zn and Cu were obviously influenced by the degree of industrial intensity and exploitation of human activities, while Ni, Cd, Pb, As and Cr were more evenly distributed. Effects of sewage sources and wastewater-treatment processes on heavy metal levels implied that different industrial wastewaters resulted in different metal contents, but the distribution of Ni, Cd, Pb, As and Cr in different treatment processes was similar. Furthermore, Hg and Cd had the strongest ecological risk, with their levels reaching severe, suggesting that sludge was not recommended for agricultural reuse in this study.