Denitrifying sulfide removal and carbon methanogenesis in a mesophilic, methanogenic culture

The inhibitory effects of 90–189 mg l−1 of sulfide and 25–75 mg-N l−1 of nitrate on methanogenesis were investigated in a mixed methanogenic culture using butyrate as carbon source. In the initial phase of 90 mg l−1 S2− test, autotrophic denitrification of nitrate occurred with sulfide as the electron donor. Then the sulfate-reducing strains converted the produced sulfur back to sulfide via heterotrophic oxidation pathway. Methanogenesis was not markedly inhibited when 90 mg l−1 of sulfide was dosed alone. When 25–75 mg-N l−1 of nitrate was presented, initiation of methanogenesis was seriously delayed. Nitrogen oxides (NOx), the intermediates for nitrate reduction via denitrification pathway, inhibited methanogenesis. The 90 mg l−1 of sulfide favored heterotrophic dissimilatory nitrate reduction to ammonia (DNRA) pathway for nitrate reduction. Possible ways of maximizing methane production from an organic carbon-rich wastewater with high levels of sulfide and nitrate were discussed.