Strongly Complexed Cu and Ni in Wastewater Effluents and Surface Runoff

Abstract

Although a variety of analytical techniques have been developed to characterize metal speciation, few have been used successfully in the complicated matrices encountered in wastewater effluents and surface runoff. In this study, competitive ligand equilibrium-cathodic stripping voltammetry (CLE-CSV) and chelating resin column partitioninggraphite furnace atomic absorption spectroscopy (CRCP-GFAAS) are used to determine the speciation of Cu and Ni in point and non-point pollutant sources discharging into South San Francisco Bay. As expected, most of the dissolved Cu and Ni in wastewater effluents and surface runoff are complexed. Moderately strong metal-complexing ligands, which likely consist of activated sludge biopolymers and humic substances, are responsible for the complexation of only about 20% of the Ni and 5-50% of the Cu. The remaining Cu and Ni is complexed by ligands with apparent stability constants comparable to those of synthetic chelating agents. Strongly complexed Cu is present at concentrations below 40 nM and accounts for 5-60% of the Cu discharged by these sources. Strongly complexed Ni is present at concentrations ranging from approximately 10 to 100 nM and accounts for >75% of the Ni discharged by wastewater treatment plants and approximately 25% of the Ni in surface runoff. Strong Ni complexes, which are not removed during wastewater treatment, are extremely stable in seawater. The existence of strong metal-complexing ligands in wastewater effluent and, to a lesser degree, in surface runoff must be accounted for when evaluating metal treatability and biogeochemistry.

Temporal Trends of Dissolved Trace Metals in Jamaica Bay, NY: Importance of Wastewater Input and Submarine Groundwater Discharge in an Urban Estuary

“…The remaining portion of the dissolved metal pool is more stable or refractory and tends to behave conservatively during mixing. The low degree of removal calculated for Cu and Ni (30% and 23%, respectively) is consistent with previous work showing that these metals tend to be strongly complexed with anthropogenic organic ligands in wastewater (Sedlak et al 1997). On the other hand, the conservative mixing behavior of Fe in the sewage estuary contrasts starkly with the nearly quantitative removal commonly observed in river estuaries (e.g., Boyle et al 1974;Sholkovitz et al 1978).…”

“…4). The good correlation between the metals and organic carbon suggests that organic complexation was a significant process regulating the solubility of Cu, Ni, and Zn in Jamaica Bay, perhaps resulting from the input of strong organic ligands from wastewater (Sedlak et al 1997).…”

Copper, lead and cadmium loads and behavior in urban stormwater runoff in Curitiba, Brazil

“…Actually, the presence of copper-complexes in surface runoff waters has been reported in the literature. 41 Sedlak et al 42 detailed the presence of moderately strong metal-complexing ligands, which are responsible for the complexation of about 5-50% of the Cu in the dissolved phase. The existence of metal-complexing ligands in surface runoff waters must be accounted for when evaluating runoff management and treating practices.…”

Trace Metals in Upland Headwater Lakes in Ireland

“…Several studies suggest that Ni complexes with organic ligands (Sedlak et al 1997;Xue et al 2001) and inorganic compounds such as hydrous oxides of Fe and Mn, and clay minerals (Boyle and Robinson 1988). In the current study, a large proportion of Ni was in the dissolved organic fraction (48 % non-labile) similar to Skjelkvåle et al (2001).…”