Organic carbon coupling with sulfur reducer boosts sulfur based denitrification by Thiobacillus denitrificans.

Sulfur autotrophic denitrification utilizes elemental sulfur as the electron donor for nitrate removal from aquatic environments. Organic carbon could stimulate the conversion of sulfur and facilitates the S-based denitrification process in the mix-trophic. In this study, the co-cultured system of sulfur reducer (Geobacter sulfurreducens) and Thiobacillus denitrificans was used to investigate that how organic carbon could boost the S-based denitrification. The results showed that the rate of S-based denitrification was improved with C/N ratio of 0.13 and this improvement continued even after the acetate was exhausted. Sulfur probe test and Raman analysis suggested that reduced sulfur species (S) were formed with the addition of organic carbon. The S could recombine with element sulfur and the bioavailability of S would be improved, as a result, the rate of S-based denitrification increased as well. Nitrate reduction rate could further increase with the C/N ratio of 0.88, but it would decrease significantly when the C/N ratio increased to 1.50 as the high concentration of generated S. Our results provided explanations that why organic carbon addition would improve the bioavailability of S which could further promote the S-dominant denitrification process.