Performance, comparison and utilization of reduced sulfur (−2) compounds (S2−, FeS and SCN−) in autotrophic denitrification process by thiosulfate-driven autotrophic denitrifier

The coexistence of reduced sulfur (−2) compounds (S2−, FeS and SCN−) are found in some industrial wastewaters due to pre-treatment of Fe(II) salts. These compounds as electron donors have attracted increasing interest in autotrophic denitrification process. However, the difference of their functions still remain unknown, which limit efficient utilization in autotrophic denitrification process. The study aimed to investigate and compare utilization behavior of these reduced sulfur (−2) compounds in autotrophic denitrification process activated by thiosulfate-driven autotrophic denitrifiers (TAD). Results showed that the best denitrification performance was observed in SCN−; while the reduction of nitrate was significantly inhibited in S2− system and the efficient accumulation of nitrite was observed in FeS system with cycle experiments continuing. Additionally, intermediates containing sulfur were produced rarely in SCN− system. However, the utilization of SCN− was limited obviously in comparison with S2− in coexistence systems. Moreover, the presence of S2− increased the accumulation peak of nitrite in coexistence systems. The biological results indicated that the TAD utilized rapidly these sulfur (−2) compounds, in which genus of Thiobacillus, Magnetospirillum and Azoarcus might play main roles. Moreover, Cupriavidus might also participate in sulfur oxidation in SCN− system. In conclusion, these might be attributed to the characteristics of sulfur (−2) compounds including the toxicity, solubility and reaction process. These findings provide theoretical basis for regulation and utilization of these reduced sulfur (−2) compounds in autotrophic denitrification process.