Copper complexation by dissolved organic matter from surface water and wastewater effluent

Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been extensively studied with respect to complexation with copper, unlike natural organic matter (NOM). Acid–base and copper titrations were conducted on both types of organic matter. Experimental copper complexation data were compared to predictions from the Windermere Humic Aqueous Model (WHAM) Version VI. We found that NOM and WWOM have ligands with similar proton binding, but the copper binding of WWOM is not well predicted by WHAM especially at low copper concentrations because the concentrations of ligands that are most important at the low copper concentrations (below 10−6 M) were found to be about 15 times higher in the WWOM. Consideration of sulfide present in the wastewater effluent does not fully explain this deviation. Due to the possibility that there exist nonhumics like biological macromolecules in WWOM, it may need to be considered as an alternative ligand to humics in toxicity and speciation predicting models like the biotic ligand model (BLM).