Examining thiosulfate-driven autotrophic denitrification through respirometry

•Stoichiometry of two-step thiosulfate-driven autotrophic denitrification was solved.•No competitive inhibition was observed between nitrate and nitrite utilization.•Nitrite accumulation depended on bacterial population and initial nitrate concentration.•Inhibition of S2O32− oxidation and denitritation appeared under 25mg N-NO2−L−1.•A nitrite acclimated culture presented an increase of 37% on denitritation activity. Anoxic respirometry was applied to characterize a sulfide-oxidizing nitrate-reducing (SO-NR) culture obtained from an anoxic biogas desulfurizing biotrickling filter treating high loads of H2S. Immobilized biomass extracted from the biotrickling filter was grown in a suspended culture with thiosulfate as electron donor to obtain the biomass growth yield and the S2O32−/NO3− consumed ratio. Afterward, respirometry was applied to describe thiosulfate oxidation under anoxic conditions. A pure culture of Thiobacillus denitrificans was also used as a control culture in order to validate the procedure proposed in this work to characterize the SO-NR biomass. Respirometric profiles obtained with this microbial culture showed that nitrite was formed as intermediate during nitrate reduction and revealed that no competitive inhibition appeared when both electron acceptors were present in the medium. Although final bioreaction products depended on the initial S2O32−/NO3− ratio, such ratio did not affect thiosulfate oxidation or denitrification rates. Moreover, respirometric profiles showed that the specific nitrite uptake rate depended on the biomass characteristics being that of a SO-NR mixed culture (39.8mgNg−1 VSSh−1) higher than that obtained from a pure culture of T. denitrificans (19.7mgNg−1 VSSh−1). For the first time, the stoichiometry of the two-step denitrification mechanism with thiosulfate oxidation and biomass growth associated was solved for both reactions.