LAUSR

The agricultural use of sewage sludge has become an economic disposal method used worldwide. However, heavy metals contained in sewage sludge have become the crucial limiting factors for this way of disposal. This study showed that regulatory limit values are not enough to determine whether sewage sludge is suitable for agricultural use; risk assessment and potential analysis should be applied. Correlation analysis and hierarchical cluster analysis (HCA) should also be performed to identify heavy metals’ sources and show their influence on sewage sludge utilization. Samples were collected from 13 wastewater treatment plants (WWTPs) located in central Shanxi Province. Results indicated that the mean contents of heavy metals in sewage sludge were all less than the limit threshold of China. According to the monomial potential ecological risk coefficient (Eri), the agricultural use of sewage sludge had low ecological risks for all heavy metals, except for Hg and Cd. Based on the potential ecological risk index (RI), only three stations had moderate risk, other nine stations all had higher potential risk. The mean potentials by all heavy metals were all beyond 10 years, which is the limit of the maximum application time specified by China. Combining all heavy metals, only one station’s potential was less than 10 years. Although the contents of heavy metals were all within the threshold values, large quantities of sewage sludge are not suitable for agricultural use. Coal-related industries, which were the main sources of Hg and Cd, greatly affected the agricultural use of sewage sludge.