Denitrifying sulfide removal with methanogenic culture

Abstract

Simultaneous sulfide, nitrate and carbon removal in the effect of nitrate and/or sulfide addition using methanogenic cultures was investigated using batch cultures. The cultures supplemented with sulfide efficiently denitrified 50–500mg N/L nitrate to nitrogen gas. The mechanism proposed was denitrification occurred via autotrophic pathway first, followed by heterotrophic pathway. Nitrate reduction pathway slightly shifted to dissimilatory nitrate reduction to ammonia (DNRA) in cultures with no addition of sulfide, starting at initial nitrate concentration 250mg N/L. Microbial community probing suggests that autotrophic denitrification were carried out by epsilon proteobacterium (Thiomicrospira denitrificans). The heterotrophic pathway was carried out by Thauera sp. in both cultures with and without the addition of sulfide.With the presence of nitrate, sulfide was oxidized to elemental sulfur in 32h after the assay began. Due to the activity of sulfate reducing strains, it was later recovered back to nearly initial concentration via heterotrophic oxidation pathway. Sole addition of nitrate at concentration 50–500mg N/L resulted in delay of methanogenesis. At concentration 750–1000mg N/L, a complete suppression occurred. The addition of nitrate along with sulfide at concentration 100mg S/L decrease methane production, while at concentration 200mg S/L, severe inhibition occurred. However, when sulfide was dose alone, the inhibition was not as severe as when it was added with nitrate. Inhibition was due to denitrification intermediates, mainly by accumulation of nitrite and nitrous oxide. Denitrification occurred first while at the same time inhibited methanogenesis.