IMPACT OF Fe/Mn-MODIFIED DRINKING WATER TREATMENT RESIDUALS ON HEAVY METALS IMMOBILIZATION IN SEWAGE SLUDGE CONTAMINATED SOIL

Recently, drinking water treatment residuals (Al-WTRs) received great attention as a low-cost immobilizing agent for heavy metals in contaminated soil in order to improve its immobilization efficiency. Al-WTR modified using some active sorbents, as Fe-Mn oxides, in this work, Al-WTR modified using Fe Cl2⋅4H2O combined with KMnO4 and we examined the impact of raw and Fe/Mn- modified Al-WTR at different rates (0, 0.5, 1.5, and 2.5%) on the chemical behavior of Zn, Cr, Cd and Pb through fractionation trial after two months of incubation .In addition, investigated bioavailability of these metals in soil through pot experiment using radish plant (Raphine's sativus) as a bio-indicator. The results showed that Fe/Mn- modified Al-WTRs has greater effect on redistribution of heavy metals among their fractions where the exchangeable, and carbonate fractions significantly decreased. However, the oxides-, organic-bound and residual fractions increased significantly (P<0.05) in the soil for all elements relative to raw Al-WTRs and untreated soil. As well, bioavailability of Zn, Cr, Cd and Pb decreased with increasing raw and Fe/Mn- Al-WTR rate. 2.5% Fe/Mn- modified Al-WTR was significantly more effective in reducing the concentrations of DTPA-Zn (up to 73.3%), -Cr (up to 65.2%), -Cd (up to 73.6%) and-Pb (up to 90.7%) in the soil. The results also demonstrated that these heavy metals concentrations in shoot and root decreased with increasing Fe/Mn- Al-WTR dosage., 2.5%Fe/Mn- modified Al-WTR decrease the percentage of Zn, Cr, Cd, and Pb in shoot by48.46, 66.24, 68.75 and 81.55% respectively. It can be suggested that modification of the raw Al-WTR increased its specific surface area, active functional groups (Fe-O and Mn-O) and CEC, which led to increasing its immobilization efficiency and played an important role in stabilization of heavy metals in the forms of oxides, organic and residual fractions.