Multiscale hydrodynamic optimization and energy valorization in hydrogen-based membrane biofilm reactors: unraveling the lumen-shell interaction

Abstract

Hydrogen-based membrane biofilm reactors (MBfR) offer a transformative approach to nitrate remediation; however, their industrial scale-up is currently hindered by limited understanding of internal hydrodynamics. This study bridges this gap via a rigorous multiscale Computational Fluid Dynamics (CFD) investigation, integrating micro-scale single-fiber dynamics with macro-scale module hydrodynamics using coupled Navier-Stokes and Darcy-Forchheimer formulations. We quantified the impact of membrane length, feed velocity, and biofilm thickness on performance. Single-fiber analysis reveals a non-linear inverse relationship between membrane length and hydrogen outflow uniformity, identifying lumen hydraulic resistance as the primary determinant of substrate availability. Notably, biofilm thickness exerts negligible influence on intraluminal hydrodynamics, suggesting gas-supply energy calculations can be decoupled from biological growth. Energy analysis confirms hydrogen pressurization as the dominant operational expenditure, 6–7 orders of magnitude higher than liquid pumping costs. At the module scale, simulations uncover significant heterogeneity in shear stress and flow channeling near the inlet. Through systematic parametric sweeps, a transverse filament spacing of 0.34 mm was identified as the optimal design point, balancing specific surface area maximization with mass transfer efficiency. These findings provide a theoretical foundation for optimizing hollow fiber bundle layouts in next-generation, energy-efficient MBfR systems.