Fate of copper in copper-complexed dyes during biological waste treatment III

Equations describing the equilibria of copper-complexed dyes during activated sludge wastewater treatment are examined in light of recent sorption measurements. Specifically, factors influencing the removal of copper from reactive and direct azo dyes are considered. The results of these calculations are consistent with experimental results which show that: (1) dissolved copper concentrations depend primarily on sorption to biosolids; and (2) sorption does not strongly affect copper removal from dissolved dye. The same equations have been used to show that employing a strong sequestrant (EDTA) in wet processing can greatly increase total dissolved copper concentrations in effluents due to competitive formation of poorly sorbed complexes. The importance of competing reactions and solids concentration is demonstrated both experimentally and mathematically. The derived equations can be used to estimate copper removal efficiency in various wastewater treatment scenarios as a function of solids concentrations and properties of dyes or complexing agents. (C) 2001 Elsevier Science Ltd. All rights reserved.