Autotrophic denitrification via nitrate as an effective approach for removal of dissolved sulfide in anaerobic reactors

This work assessed the effect of adding different concentrations of nitrate (50-300 mg NO3-center dot L-1) on the removal of dissolved and gaseous sulfide in an anaerobic reactor treating synthetic effluent containing sulfate (100 mg SO42-center dot L-1) and organic matter (1 g COD center dot L-1). Autotrophic denitrification, stimulated by the addition of nitrate, was demonstrated to be a very effective approach for removal of dissolved sulfide even in the presence of a high concentration of organic matter (complete removal with 50 mg NO3- mg center dot L-1). However, it had a minor effect on H2S(g). Sulfide remained partially oxidized to elemental sulfur even with excess nitrate (100-300 mg NO3- mg center dot L-1). Therefore, the competition for this electron acceptor between the autotrophic and heterotrophic denitrification pathways may have prevented the conversion of the generated sulfide into sulfate again. No evidence of inhibition of methanogenesis and sulfidogenesis was found during nitrate supplementation.