Abstract

Competition between methanogenic bacteria (BPM) and sulfate reducing bacteria (BRS) for acetate and hydrogen has been a limiting factor in the process of anaerobic digestion. Since has been shown that BPM have a comparatively greater capacity for adhering to surfaces, immobilization of these bacteria on support media may be a method for favoring their presence. This work has studied the formation of biofilms by BPM and BRS trophic groups on ceramic and polyethylene support materials. The results suggested that the hydrogenotrophic BPM attained growth rates on ceramic of 0.061 h-1 and on polyethylene of 0.030 h-1, with counts of 5.5 × 107 Most Probable Number (MPN) ml-1 on ceramic and 1.1 × 108 MPN ml-1 on polyethylene. These values were significantly higher than those of other trophic groups among the methanogens which were studied (acetotrophs, formatotrophs, and methylaminotrophs). In all cases the BRS attained lower values of maximum growth rate than the BPM. Rates for acetotrophic BRS were 0.009 h-1 on ceramic and 0.008 h-1 on polyethylene, with counts of 6.7 × 106 MPN ml-1 on ceramic and 4.2 × 106 MPN ml-1 on polyethylene. Statistical analyses showed these values to be significantly higher (p?0.05) than values for hydrogenotrophic BRS. In both BPM and BRS communities, the proportions of their respective trophic groups in suspension (no supports) were different from those observed in systems containing supports, on which they formed biofilms. It was observed that hydrogenotrophic and methylaminotrophic BPM were those best retained on ceramic and polyethylene.