High rate autotrophic denitrification in fluidized-bed biofilm reactors

• High rate, high efficiency autotrophic denitrification was demonstrated in a FBR.
• Complete nitrate and nitrite removal was achieved at HRTs as low as 10 min.
• The nitrate and nitrite loading rates reached 600 and 228 mg L−1 h−1, respectively.
• The biofilms were dominated by T. denitrificans and tolerated pHs as low as 5.8.
• The optimal temperature for nitrate removal was 26.6 °C based on Ratkowsky modeling.

High rate, high efficiency thiosulfate-driven autotrophic denitrification and denitritation with Thiobacillus denitrificans dominated biofilms were achieved in fluidized-bed reactors (FBRs) operated at 20.0 ± 2.0 and 30.0 ± 0.2 °C. Complete nitrate removal was obtained even at nitrate loading rate and hydraulic retention time (HRT) of 600 mg L−1 h−1 and 10 min, respectively. Further decrease of HRT to 5 min resulted in 50% of nitrate removal efficiency. Nitrite did not accumulate when nitrate was used as electron acceptor unless HRT was decreased to 5 min. Effluent pH remained at 5.8 during denitrification. When nitrite was supplemented as the electron acceptor, denitritation effectively proceeded with the highest nitrite loading rate of 228 mg L−1 h−1. Similar denitrification and denitritation performances were obtained at 20.0 ± 2.0 and 30.0 ± 0.2 °C. Batch assays conducted at temperature range from 1 to 46 °C, however, showed a significant impact of temperature on autotrophic denitrification. Ratkowsky model was used to estimate the minimum, optimal and maximum growth temperatures of T. denitrificans dominated culture that were below 1, 26.6 and 50.8 °C, respectively.