METAL-INDUCED INHIBITION OF ANAEROBIC METABOLISM OF VOLATILE FATTY-ACIDS AND HYDROGEN

The effects of copper (Cu), chromium (Cr), cadmium (Cd), lead (Pb) and zinc (Zn) on the biotransformation of organic acids (acetate, propion ate and butyrate) and H-2 were assessed in serum-bottle microcosms. Ex periments were performed over a range of metal concentrations (20-200 mg/l) using biomass from an anaerobic bioreactor fed continuously with ethanol distillery waste as inoculum. In general, the added metals in hibited the biotransformation of organic acids with increasing metal c oncentration. However, the extent of inhibition varied for the differe nt biotransformations and for the different metals tested. For example , the concentration of CuCl2 effecting a 50% reduction in the rate con stant for biotransformation of acetate, propionate and butyrate was 60 , 75 and 30 mg/l, respectively. Cu and Cr (VI) were the most inhibitor y metals in organic acid transformation, whereas Pb was the least toxi c. The rate of biotransformation of acetate was reduced by half at Cu and Cr concentrations of 60 and 40 mg/l respectively, whereas Cd, Pb, and Zn concentrations of 160 to 200 mg/l had little effect. The activi ties of hydrogenotrophic methanogens were much less affected by the sa me metals and metal concentrations.