Heavy Metal Uptake by Sludge Particulates in the Presence of Dissolved Organic Matter

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Courtesy of Weston Solutions, Inc


The presence of dissolved organic matter (DOM) significantly affects the uptake of heavy metals by sludge particulates. The uptake of seven metals including Cu(II), Ni(II), Co(II), Pb(II), Zn(II), Cd(II), and Cr(III) by sludge in the presence of DOM was investigated. Results showed that the uptake of heavy metals increases with pH at neutral and low pH conditions. In the alkaline pH region, the organic matter dissolution increases significantly. As a result, the uptake of the metal-DOM complexes, specifically, Cu(II), Ni(II), and Co(II), decreases. The uptake of other metals such as Pb(II), Cd(II), Zn(II), and Cr(III), however, is not significantly affected by the presence of DOM. Results also showed that Pb(II), Cr(III), and Cu(II) are the most uptakable metals among the seven metals studied, and Ni(II) and Co(II) are the least uptakable.

A mathematical model was developed to describe the uptake of heavy metals in systems containing DOM using pH as the master variable. In relatively low metal concentrations, a much simplified version of the model can be used. The stability constants of metal-sludge complexes and metal-DOM complexes can be determined using both models. Results showed that stability constants of Cu(II)-sludge complex (logKS) and Cu(II)-DOM complex (logKL) are 4.9 and 4.4, respectively. They are 3.0 and 2.4 for Ni(II)-sludge complex and Ni(II)-DOM complex, respectively. The models can well describe the metal uptake by sludge at various DOM and pH conditions.

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