Coupling Hydrodynamics and Biofilm Detachment to Predict Iron Bioreduction by Shewanella oneidensis MR-1

Abstract

Hydrodynamic conditions strongly regulate the biofilm structure and consequently the rate of dissimilatory Fe(III) bioreduction by Shewanella oneidensis MR-1. To elucidate this relationship, column experiments and in situ flow cell observations were performed under varying flow velocities and initial biofilm biomass. A reactive transport model was then developed, incorporating biofilm detachment kinetics and biofilm surface area-dependent Fe(III) reduction rates, to simulate the spatiotemporal distribution of Fe(III) and Fe(II) across these flow regimes. Results showed that a higher flow velocity (1.1 × 10^–5 m/s) generated greater shear stress, causing extensive biofilm detachment, which significantly lowered Fe(III) reduction rates compared to low-flow conditions. Despite substantial detachment at a high flow, the residual attached biofilm continued to reduce Fe(III), yielding a steady-state Fe(II) fraction of 17%. The model accurately captured the observed flow-dependent bioreduction dynamics, underscoring the critical role of hydrodynamics in controlling the biofilm thickness and activity. These findings highlight the necessity of incorporating hydrodynamic impacts on the biofilm structure into biogeochemical models to improve the predictions of iron cycling in complex aquatic environments.

Biofilm thickness controlled by hydrodynamics determines the iron bioreduction rate, which also affects the distribution and migration of the iron in the environment.