TOXICITY OF ELECTROPLATING METALS ON BENZOATE-DEGRADING GRANULES

Toxicity of five electroplating metals on the activity of biogranules, which were obtained from an upflow anaerobic sludge blanket (UASB) re actor treating benzoate-rich wastewater, was investigated in this stud y. The methanogenic activities of the biogranules were measured in ser um vials using wastewaters containing not only benzoate as substrate, but also individual heavy metals over a wide range of concentration. A t 37 degrees C, the toxicity, which increased with metal concentration , was in the following descending order: nickel >zinc >cadmium >copper >chromium. The biogranules exhibited higher resistance to metal toxic ity than the flocculent anaerobic sludge. This is probably due to the densely packed nature of the biogranules, reducing the overall exposur e of bacteria to the toxic metals in the bulk solution. This implies t hat granulation of biomass increases their resistance towards toxicant s in the wastewater.