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

Abstract

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 TM 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.

The effect of wastewater effluent derived ligands on copper and zinc complexation

“…The data presented here shows that the complexation characteristics of the effluent-derived organic matter offer a substantially greater (DOC normalised) capacity to complex copper and zinc than those derived from natural sources, which was also consistent with findings from other similar studies (van Veen et al 2002; Sarathy and Allen 2005; Chaminda 2013). In their study, Sarathy and Allen (2005) proposed that up to 90% of the difference between river water and effluent copper complexation might be attributable to the influence of sulphide for which unprotonated sulphide clusters have been observed by others to form highly stable copper complexes (Rozan et al 2000) (thermodynamic stability constant log β >54); however, since the average binding affinity values for the effluents in the present study were lower than the values for the SRFA sample, the additional complexation capacity observed for the sewage effluents is unlikely to have been substantially attributable to such a strongly binding ligand.…”

“…Previous studies have shown that wastewater effluent ligands are capable of binding trace elements present in the matrix to a greater degree than naturally derived DOC from, for example, standard Suwannee River humic and fulvic acids (Chaminda et al 2008, 2013) or that derived from road runoff (Chaminda et al 2010). Furthermore, effluent-derived DOC has been shown to be different in form compared to DOC derived from natural sources.…”

Preliminary Toxicity Assessment of Combined Sewer Overflows in Toyama, Japan

“…The proportion of free ionic plus unstable complexed metals in these samples, which was measured by chelating disk cartridge, was 57 − 76% for Cu, 31 − 53% for Zn, 28 − 51% for Pb, 19 − 25% for Ni. The similar trend is reported in effluent samples of wastewater treatment plants (WWTPs) [46]. More than 55% of the dissolved metals were strongly complexed by ligands in the effluents.…”

Correlations between aromaticity of dissolved organic matter and trace metal concentrations in natural and effluent waters: A case study in the Sagami River Basin, Japan

“…Therefore, the WWTP-derived metal-binding ligands with low SUVA 254 may also occur in the SRB main stream to some extent and potentially increase [Cu] Table S5). In addition to the anthropogenic ligands, hydrophilic DOM fraction and dissolved sulfides originated from urban effluents may affect trace 20 metal speciation due to their high binding affinities to trace metals (Chaminda et al, 2013;Louis et al, 2014;Matar et al, 2015;Rozan et al, 2000).…”