EFFECT OF HEAVY-METALS ON ACIDOGENESIS IN ANAEROBIC-DIGESTION

The effects of chromium, cadmium, lead, copper, zinc and nickel on volatile fatty acid (VFA) production in anaerobic digestion were studied using serum bottle assays. Glucose acclimated seed sludge was used. The relative toxicity of heavy metals to production of acetic acid (HAc) and n-butyric acid (n-HBu) was Cu > Zn > Cr > Cd > Pb > Ni and Cu > Zn > Cr > Cd > Ni > Pb, respectively. Cu was the most and Pb was the least toxic heavy metals to VFA-producing organisms. An increase in HAc production was observed when the concentration of Ni was less than 300 mg l-1. The sensitivity of VFA production to metallic inhibition was n-HBu > HAc for the tested metals except Pb which had the same level of inhibition to the production of the two VFAs. Except Cu with Ni, mixtures of the other tested heavy metals caused synergistic inhibition on total VFA production. Some metal mixtures increased the production of HAc markedly.