Distribution Of Chemical Fractions And Potential Mobility Of Heavy Metals During Bio-treatment Process Of Municipal Wastewater

The major restrictive factor for agronomic application of sewage sludge is heavy metals concentrated in sewage sludges. The environmental behavior of heavy metals depends strongly on their specific chemical fractions or binding ways in sludges. The fraction distributions of heavy metals in sludges, which collected from each treatment stage of two typical municipal wastewater treatment plants of China, were investigated in present work. The potential mobility and bio-availability of heavy metals in sludges were also studied. The main conclusions drawn from present study were listed as follows.(1) These sludges showed high potential agricultural benefits, as well as some eco-toxicities. The physicochemical properties of sludge differed from sludges generated from different treatment stages of the treatment process. The characteristics of the final disposal sludges were determined mainly by the characteristics of the primary sludge.(2) Heavy metals could be removed effectively during the biological treatment process of municipal wastewater. The removal ratios of heavy metals in wastewater influenced significantly by the concentrations and chemical fractions of metals, and the concentration of SS, BOD and COD in wastewater.(3) The distribution of chemical fraction for heavy metals and the physicochemical properties of wastewater influenced significantly by the wastewater process. And similar change trends could be identified for each physicochemical parameter along the wastewater treatment process.(4) The stabilities of heavy metals in sludges increased along the municipal wastewater treatment process. Fe, Ni, Cr, and Mo distributed mainly in the residual fraction, and Cu and Pb mainly in the oxidizable and residual fraction in sludges. While for Mn and Zn, no significant distribution laws could be identified among sludges generated from different treatment stages of the wastewater treatment process. The distribution of heavy metals fraction influenced significantly by the characteristics of metals, and the compositions and the properties of sludges. Additionally, the extent and ways of the influences on the chemical fractions of metals by the properties of sludges differed from the metals kinds.