Influence of flow velocity on denitrification in a pore-scale lab experiment
Résumé
Assessing and understanding aquifers reactivity is an important issue worldwide. In these aquifers, a variety of flow velocities may rule the reactivity development, and the reaction efficiency. Only few studies assessing the influence of this physical parameter on the biochemical reactivity have been carried out yet. We present an experimental setup, where denitrification occurs in 2mm diameter reactive tubes for different flow velocities which control the fluid residence-time and may impact on reaction kinetics. Conversely to most of the experiments, the carbon source is the tube itself and C is present in a homogeneous manner all along the tubes. This experiment shows reaction kinetics close to the ones observed at the field- or lab-scale with aquifer material (both water and rocks). Results show that the setting up time of the reactivity (ruled by the bacterial biofilm development) is not highly influenced by the flow velocity [from 40 to 6 mm/min]. On the contrary, the stabilization and the maximum reaction rate depend on the flow velocity. The concentration profiles made along the flow lines exhibit a homogeneous reactivity along the tubes at the beginning of the experiments. The reactivity becomes localized and migrates towards the tube inflow with increasing time. This experiment provides useful information on the time scale needed for in situ reactivity assessments and for the building up of a reactivity model, in which the minimum concentration is controlled by fluid velocity whereas the initial reaction phase concentration