Toxicity of copper to acetoclastic and hydrogenotrophic activities of methanogens and sulfate reducers in anaerobic sludge

Heavy metals could potentially negatively impact microorganisms in anaerobic sulfate reducing bioreactors. The objective of this is study was to evaluate the inhibitory effect of copper to acetoclastic and hydrogenotrophic activities of methanogens and sulfate reducers in sludge obtained from a full-scale sulfate reducing bioreactor. The 50% inhibiting concentration (50%IC) of Cu²⁺ to acetoclastic and hydrogenotrophic methanogens was 20.7 and 8.9 mg l^-1, respectively. The 50%IC of Cu²⁺ to acetoclastic sulfate reduction was 32.3 mg l^-1. The hydrogenotrophic sulfate reducers were only inhibited by 27% at the highest concentration of Cu²⁺ tested, 200 mg l^-1, indicating a high level of tolerance. The soluble Cu²⁺ was observed to decrease rapidly in both the methanogenic and sulfate reducing assays. The highest level of decrease was observed in the hydrogenotrophic sulfate reducing assay which was over 99% in 5 h. The results of this study indicate that sulfate reducing biotechnologies would be robust at relatively high inlet concentrations of Cu²⁺.