Effects of Bioavailable Cadmium on Anaerobic Systems

The research objective was to develop a correlation between bioavailable cadmium (Cd) and toxicity in anaerobic systems. Toxicity assays were performed with acetate-using methanogens in serum bottles. The bioavailable, free dissolved Cd was measured at the end of the experiments after separation in cation-exchange resin inside dialysis bags placed in the cadmium-spiked serum bottle samples at the end of the experiments. Measured free soluble Cd showed a good correlation with inhibition of gas production. Up to 0.09 mg/L caused ≤5% inhibition, whereas concentrations of 0.12 mg/L and higher showed >90% inhibition. Measured total soluble cadmium failed to show a good correlation with inhibition of gas production. Systems with total suspended solids (TSS) exceeding 2 400 mg/L showed less inhibition than systems with TSS of approximately 1 400 mg/L. However, when bioavailable Cd was less than 0.09 mg/L, systems with the lower TSS showed little inhibition even with spiked Cd concentrations as high as 100 mg/L.