Carbon flow in acetotrophic enrichment cultures from pulp mill effluent treatment

Anaerobic acetate utilizing cultures were enriched from three different environments of pulp mill wastewater and subsequently subcultured on calcium acetate and calcium acetate plus sodium sulfate media. Microbial acetate conversion was complete in all cases where methanogens tolerant to sulfur compounds were present, even at 4.6 g SO₄^2-/l. Acetate conversion by sulfate reduction was significant only in methanogenic cultures sensitive to sodium sulfate or its metabolic products. Sulfate reduction was always incomplete although acetate was present in excess. Sulfate reducing capacity persisted in continuous cultivation of sludge for at least 2 years in the absence of oxidized sulfur compounds. Tolerance of acetotrophic methane-producing bacteria from pulp mill wastewater sludge towards sulfur compounds (sulfate plus its metabolites) was preserved beyond an experimental exposure of 6 months (6 transfers) to acetate-only medium. Another methanogenic enrichment culture from pulp mill sludge developed sensitivity towards sulfur compounds after being continuously cultured in an environment lacking oxidized sulfur compounds for 2 years.