Biofilm formation behind a backward facing step*

Flow properties, such as wall shear stress, and nutrient availability have been shown to influence the formation of biofilm. Disentangling wall shear stress and nutrient transport is still a challenge. Prior studies have mostly focused on straight channels or pipes where homogeneous conditions are encountered at the walls. We aim to connect the study of biofilm formation with the case of a backward-facing step type flow. Within the recirculation area, nutrient transport is dominated by diffusion processes, whereas outside of it advection dominates. The influence of spatially varying shear stress and nutrient availability on biofilm formation is investigated. The morphology of a pseudomonas fluorescens biofilm forming behind the backward-facing step is measured using optical coherence tomography. We show that early biofilm growth is concentrated in areas with low velocities that are still dominated by advective nutrient transport as well as the stagnation point.