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-Nl(-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)S(2-) 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-Nl(-1) of nitrate was presented, initiation of methanogenesis was seriously delayed. Nitrogen oxides (NO(x)), 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.