INHIBITION OF BIOACTIVITY OF UASB BIOGRANULES BY ELECTROPLATING METALS

Among the high-rate anaerobic wastewater treatment processes, the upfl ow anaerobic sludge blanket (UASB) reactor has attracted most commerci al and research interests. In this study, the toxicity of five heavy m etals commonly found in the electroplating effluent on the activity of anaerobic biogranules was investigated. Biogranules were sampled from UASB reactors treating four types of wastewaters containing, individu ally, acetate, propionate, starch and benzoate as the sole substrate. All reactors were operated at 37 degrees C for over six months at a lo ading rate of 10 g COD(-1)d(-1). The methanogenic activity of biogranu les treating each type of wastewater decreased with the increase of me tal concentration. The toxicity of each metal to the biogranules was m easured by the reduction of methanogenic activity of biogranules in se rum vials, as compared to the controls. Results show that, in general, acetate- and propionate-degrading biogranules exhibited higher resist ance to electroplating metals than the starch- and benzoate-degrading ones. Acetate conversion is a one-step process conducted by acetotroph ic methanogens alone. Propionate degradation, on the other hand, is a two-step process conducted by acetogens and methanogens; whereas, benz oate and starch degradations are multi-step processes conducted jointl y by fermentative/acidogenic bacteria, acetogens and methanogens. Resu lts of this study imply that heavy metals from electroplating effluent , in general, inhibit the bioactivities of fermentative/acidogenic bac teria more than those of methanogens and acetogens. For the latter two groups of bacteria, the toxicity of the heavy metals were in the foll owing descending order: zinc > nickel > copper > cadmium > chromium.