EFFECTS OF SLUDGE FROM WASTEWATER TREATMENT PLANTS ON HEAVY METALS TRANSPORT TO SOILS AND GROUNDWATER

Heavy metals accumulation in soils under the application of sewage sludge and effluent from wastewater treatment plants is a major environmental concern. Transport of heavy metals through the soils may eventually lead to the groundwater contamination and their accumulation in soils and crops. Silt loam soils covered by sludge and effluent of Tehran wastewater treatment plant were used in this study. The vertical and horizontal distributions of sludge-borne Cd, Cr, Zn, Pb, Fe, Cu and Ni were studied within four plots. Measured loadings of heavy metals to the plots from the sludge application were Fe, 284.75; Pb, 90.28; Zn, 109.5; Ni, 60.28; Cu, 27.76; Cr, 28.58 and Cd, 4.5 mg/kg. Two hundred and forty soil samples were taken from areas within the plots and up to 100 cm depth on each side of the plots. Leachate water from the plots which contaminates groundwater was collected and the concentrations of heavy metals were measured. The determined concentration of sludge-borne in leachate Cr, Ni, Zn, Fe, Pb, Cu and Cd were 0.803, 0.785, 0.532, 0.439, 0.110, 0.180 and 0.019 mg/l respectively. The results of this study can be used for the management of effluent and sewage application in agricultural lands and crop production. The groundwater quality can be monitored and improved as well.