Effect of organics on sulfur-utilizing autotrophic denitrification under mixotrophic conditions

Sulfur-utilizing denitrification can be performed by denitrifying sulfur bacteria under autotrophic and heterotrophic conditions. To investigate the effect of organics (methanol and landfill leachate) on sulfur-utilizing denitrification, six laboratory-scale sulfur packed columns were operated under autotrophic, mixotrophic and heterotrophic conditions for approximately 1 year. The performance of the columns was monitored by measuring the pH, nitrate, nitrite, sulfate, sulfide, alkalinity dissolved organic carbon (DOC), and turbidity. These tests indicated that the mixotrophic column had a higher nitrate removal capacity than the autotrophic column. It was also found that under mixotrophic conditions, some portion of nitrate was removed heterotrophically and the remainder was denitrified by sulfur-utilizing autotrophic bacteria without inhibition by organics. In addition, sulfate production and alkalinity consumption were reduced under mixotrophic conditions. These results suggest that mixotrophic conditions that allow simultaneous reactions of autotrophic and heterotrophic denitrification provide significant advantages in terms of nitrate and DOC removal, sulfate production decrease, and alkalinity consumption over obligate autotrophic or heterotrophic denitrification.