[Study on sulfur-based autotrophic denitrification with different electron donors].

Sulphur-based autotrophic denitrification was applied to treat the low concentration nitrate-contaminated water. Different electron donors, namely, elemental sulfur, sulfide and thiosulfate, were used in three continuous reactors to compare the denitrification performance. When treating the low concentration nitrate-contaminated water (13 mg x L(-1)), the thiosulfate system showed the best performance and the sulfide system was the worst. The thiosulfate system was less sensitive to low temperature than the other two. At temperatures higher than 20 degrees C, the sulfur system was greatly influenced by mass transfer efficiency and HRT. It removed 81% of nitrate and 79% of TN when HRT was no less than 2 h, but could only achieve a low nitrate and TN removal rate of 47% and 51% when HRT was shorter than 2 h. No obvious nitrite accumulation was observed and the average effluent nitrite was 0.53 mg x L(-1). The sulfide system could only remove 47% of nitrate and 41% of TN with 0.29 mg x L(-1) nitrite in the effluent at the HRT of 4 h. Meanwhile, the thiosulfate system had a high removal rate of 99% for nitrate and 90% for TN, with a low content of effluent nitrite of 0.080 mg x L(-1), and the HRT could be shortened to 0.5 h. The molecular biological analysis showed that different bacteria predominated in the three reactors, and that Thiobacillus denitrificans existed abundantly in the sulfur system, while the functional bacteria in the sulfide and thiosulfate systems could not be identified yet. A new species of sulfur-based autotrophic denitrification bacterium may have been found.