COMPETITION BETWEEN METHANOGENS AND SULFATE REDUCERS - EFFECT OF COD SULFATE RATIO AND ACCLIMATION

A discussion of the current understanding of the competition between sulfate-reducing bacteria and methanogens is presented. The effect of artificially elevated sulfate and sulfide levels on anaerobic utilization of lactate was investigated using acclimated and unacclimated inoculum. The lactate degradation pathway was observed to be dependent upon the degree of acclimation to various chemical oxygen demand (COD):sulfate ratios. A ratio of 3.7 g/g resulted in a nonsulfate reducing pathway producing propionate and acetate as products, while a ratio of 1.6 g/g resulted in a sulfate reducing pathway producing only acetate as an organic product. The change in metabolic pathways dramatically changed the relative sulfide sensitivity of the methanogens and the sulfate reducers.