Effect of heavy metals on the methanogenic UASB granule

The effects of ionic chromium, cadmium, lead, copper, zinc, and nickel on the methanogenic UASB granule were examined by using serum bottle assays. Granular seed sludge was acclimated with a mixture of acetic (HAc), propionic (HPr) and butyric (HBu) acids. According to those results, the metal effects relied on the kinds of metal, zones of sludge, types of volatile fatty acid (VFA) and hydraulic retention time (HRT). The relative toxicity of the metals to total VFA degradation was Cu>Cr>Cd Zn>Ni Pb for both bed and blanket sludges; however, different degrees of toxicity were observed for individual VFAs and sludges. For the degradation of total VFA, the copper toxicity resistance of blanket sludge was lower than that of the bed sludge. The biogranulesʹ VFA degradation activity reduced by 50% for the biomass that came into contact with 26–3200 mg/L of the tested metals. Compared with an UASB acidogenesis process, the biogranules in the methanogenesis process exhibited a higher sensitivity to metal toxicity than the biogranules in the acidogenesis process. However, in the biogranules of methanogenesis process the HPr- and HBu-degrading acidogens were more sensitive in activity to copper than HAc-degrading methanogens. Besides, long HRT increased the toxicity resistance of HAc-degrading methanogens but decreased that of HPr- and HBu-degrading acidogens.