Influence of Cu²⁺ and S^2- on denitrifying activated sludge

The sodium sulfide method is a key treatment strategy for chelated-copper compounds in electroplating wastewater that is a too complicated process for the complete removal of these compounds, reducing such toxic residues as Cu²⁺ or S^2-. Both of these ions affect biochemical processes, but data on the influences of Cu²⁺ and S^2- on denitrifying activated sludge are relatively scarce, even though these ions may degrade the system performance. In this study, we compared the toxicities and inhibitions of Cu²⁺ and S^2- on denitrifying activated sludge. Moreover, the tolerance of Cu²⁺ and S^2- and the sludge properties were studied by performing long-term experiments. The results showed that the median effective concentrations (EC₅₀) of Cu²⁺ and S^2- for denitrifying activated sludge were 3.15 mg·L^-1 and 14.71 mg·L^-1, respectively. The observed cumulative effects indicated that the maximum tolerance concentration of S^2- for denitrifying activated sludge was 20 mg·L^-1 higher than that of Cu²⁺ (1 mg·L^-1). Moreover, the precipitation and dewatering were hindered more by the accumulation of Cu²⁺ than by the accumulation of S^2-.