Metal (Zn, Cu, Cd and Ni) Complexation by Dissolved Organic Matter (DOM) in Wastewater Treatment Plant Effluent

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Eight effluent samples were collected from four conventional activated sludge wastewater treatment plants (WWTPs) to determine the complexation of Zn, Cu, Cd and Ni by dissolved organic matter (DOM) in WWTP effluent. The collected effluents were subjected to determine the labile Zn, Cu, Cd and Ni concentrations using Empore<SUP>TM</SUP> chelating disk cartridge. It was observed that more than 55% of the dissolved metals were strongly complexed by ligands in the effluents. In addition, the Zn, Cu and Cd titration data obtained by square wave anodic stripping voltammetry were interpreted with Scatchard linearization to determine the conditional stability constant and the total binding site concentrations of DOM in three of the WWTP effluents. The titration data for Zn and Cu fitted to a two-ligand system while Cd data represented a one-ligand system. The conditional stability constant for Cu was greater than that for Zn with DOM in WWTP effluents. Zinc complexation parameters in natural organic matter (river water DOM and Suwanee River humic substances) were also compared with those of DOM in WWTP effluents. The results demonstrated higher stability constant and higher binding site concentrations for the DOM in WWTP effluents than the natural organic matter.