The influence of metal ion mixtures on the activity of activated sludge

Environmental contamination with heavy metals is inherent in the development of industries. They can be present in municipal and industrial wastewaters, reach biological wastewater treatment plants (WWTPs), and affect the performance of the activated sludge process. Moreover, heavy metals almost never occur in isolation and are components of toxic mixtures. Therefore in this study, the influence of binary metal mixtures Cd–Cu, Cd–Zn, and Cu–Zn on activated sludge dehydrogenase activity was evaluated. Two different models were used to identify possible interactions between mixture components: the concentration addition (CA) model and the independent action (IA) model. It seems that the mode of toxic interaction between mixture components strongly depends on the chosen prediction model and measured endpoint. The joint toxicity of studied mixtures was better described by the IA model compared to the CA model.