Inhibition of heavy metals on fermentative hydrogen production by granular sludge

This study was conducted to investigate the toxicity of six electroplating metals on the H2-producing activity of a granular sludge sampled from an H2-producing upflow reactor treating sucrose-containing wastewater. The H2 production activities of the sludge were measured in serum vials using wastewater containing not just sucrose and proper nutrient, but also individual heavy metals at concentrations ranging 0–5000 mg l−1. The relative toxicity to H2 production was found in the following order: Cu (most toxic) ≫ Ni ∼ Zn > Cr > Cd > Pb (least toxic). The CI,50 values, at which the bioactivity of the sludge was reduced to 50% of the control, for individual heavy metals were Cu 30 mg l−1, Ni and Zn 1600 mg l−1, Cr 3000 mg l−1, Cd 3500 mg l−1, and Pb >5000 mg l−1. Compared with the literature data, H2-producing sludge exhibited in general higher resistance to metal toxicity than methanogenic granular sludge.