HEAVY METALS CONCENTRATION OF SEWAGE SLUDGE AND ECOLOGICAL RISK ASSESSMENT FOR AGRICULTURE IN XUCHANG CITY, CHINA

Heavy metals of sewage sludge are one of restricted factors for its agriculture utilization. Twelve sludge samples in Xuchang city were collected and determined the concentration of heavy metals (Zn, Cr, Cu, Ni, Pb, As), the contamination levels and ecological risk were evaluated using the geo-accumulation index and potential ecological risk index. The results show that the Zn, Cr, Cu, Ni, Pb and As concentrations are 224.6 similar to 15359.9 mg/kg, 14.7 similar to 2818.1 mg/kg, 95.8 similar to 1252.5 mg/kg, 4.3 similar to 1218.0 mg/kg, 11.3 similar to 74.2 mg/kg and 1.3 similar to 41.8 mg/kg, respectively. Zn, Cr, Cu and Ni exceeded the control standards from agricultural use of China in several samples. The results of I-geo indicated that Pb and As are considered uncontaminated, and Zn, Cr, Cu and Ni are the main pollutants in the sludge of Xuchang city, which present the moderately/strongly contaminated to strongly/extremely contaminated level. The rank of potential ecological risk coefficient is Cu> Zn> Ni> Cr> As>Pb. Potential ecological risk index indicated that TN, QY, CWH and SD sewage sludge samples have extreme high to moderate ecological risk on environment, which consistent with the concentration of heavy metals and I-geo assessment result, and suggest that sludge samples from those plant must be taken harmless and stabilizing treatment before agriculture utilization