Impact of flow velocity on biochemical processes – a laboratory experiment

Abstract

Understanding and predicting hydraulic and chemical properties of natural environ-ments are current crucial challenges. It requires considering hydraulic, chemical and biological processes and evaluating how hydrodynamic properties impact on biochem-ical reactions. In this context, an original laboratory experiment to study the impact of 5 flow velocity on biochemical reactions along a one-dimensional flow streamline has been developed. Based on the example of nitrate reduction, nitrate-rich water passes through plastic tubes at several flow velocities (from 6.2 to 35 mm min −1), while ni-trate concentration at the tube outlet is monitored for more than 500 h. This experi-mental setup allows assessing the biologically controlled reaction between a mobile 10 electron acceptor (nitrate) and an electron donor (carbon) coming from an immobile phase (tube) that produces carbon during its degradation by microorganisms. It results in observing a dynamic of the nitrate transformation associated with biofilm develop-ment which is flow-velocity dependent. It is proposed that the main behaviors of the reaction rates are related to phases of biofilm development through a simple analytical 15 model including assimilation. Experiment results and their interpretation demonstrate a significant impact of flow velocity on reaction performance and stability and high-light the relevance of dynamic experiments over static experiments for understanding biogeochemical processes.