Experiments and Numerical Modelling of Microbially-Catalysed Denitrification Reactions

Laurent André (1) , Hélène Pauwels (1) , Marie Christine Dictor (1) , Marc Parmentier (1) , Mohamed Azaroual (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Denitrification processes have been studied for many decades in both the laboratory and the field, and current work investigates heterotrophic and autotrophic denitrification reactions. Physical, chemical and microbiological parameters have been shown to control these degradation processes and the fate of nitrogen. In this paper, we describe results and modelling of denitrification reactions in batch and flow-through column experiments. The processes controlling the fate of nitrate and, more specifically, its reduction mediated by micro-organisms are explained in detail by a multi-step process. Modelling involves a rate law describing microbial respiration. Batch experiment data and the results of thermo-kinetic modelling of biogeochemical processes are in relatively good agreement, indicating that the coupled numerical approach is suitable for simulating each individual mechanism involved in denitrification phenomena. The calculated mass-balance indicates that about 40 % of the carbon from acetate is used for anabolism and 60 % for catabolism. The kinetic parameters estimated from the batch experiments are also suitable for reactive transport modelling of laboratory flow-through column experiments. In these experiments performed on pyrite-bearing schist, 80 % of the nitrate reduction is attributed to heterotrophic micro-organisms and 20 % to autotrophic bacteria. These results also indicate that for denitrification in the presence of acetate, the thermodynamic factor in the coupled thermodynamic/kinetic law can be disregarded and denitrification kinetics will be governed, for the most part, by electron donor/acceptor concentrations. This consistency between the results of closed and open systems is a prerequisite for the field-scale use of this type of numerical approach and the efficient and safe management of nitrogen sources. Breaking down the process into several steps makes it possible to focus on the main parameters that enhance the denitrification rate.

Domaines: Géochimie; Milieux et Changements globaux

Laurent André, Hélène Pauwels, Marie Christine Dictor, Marc Parmentier, Mohamed Azaroual. Experiments and Numerical Modelling of Microbially-Catalysed Denitrification Reactions. Chemical Geology, 2011, 287, pp.171-181. ⟨10.1016/j.chemgeo.2011.06.008⟩. ⟨hal-00617602⟩