Investigating the kinetics of autotrophic denitrification with thiosulfate: modeling the denitritation mechanisms and the effect of the acclimation of SO-NR cultures to nitrite

In this work the kinetics of a number of sulfide-oxidizing nitrate-reducing (SO-NR) cultures acclimated and not acclimated to nitrite were characterized. Anoxic respirometry coupled to kinetic modeling of respirometric profiles was the methodology used to study the two-step denitrification associated to thiosulfate oxidation. Autotrophic denitritation was initially studied in a non-acclimated SO-NR culture to confirm that nitrite reduction kinetics could be described through a Haldane-type equation. Afterwards, a kinetic model describing the two-step denitrification (NO3 → NO2 → N2) was calibrated and validated through the estimation of several kinetic parameters from the fitting of experimental respirometric profiles obtained using either nitrate or nitrite as electron acceptors for both acclimated and non-acclimated biomass. The model proposed was a multi-substrate model that considered all the species implicated in the process as well as the stoichiometry associated particularly to the biomass studied in this work. A comparison between the kinetic parameters with the biomass acclimated and nonacclimated to nitrite revealed a 7-fold increase of the Haldane nitrite inhibition constant in the acclimated biomass with respect to the non-acclimated while the nitrite half-saturation constant and the maximum specific growth rate remained almost unchanged. The Fisher Information Matrix method was used to obtain the confidence intervals and also to evaluate the sensitivity and the identifiability in model calibration of each kinetic parameter estimated.