Computational Fluid Dynamics Reveals Mass Transfer Limitations in a Pilot-Scale Microbial Electrolysis Cell

Area of Science:

• Environmental Engineering
• Bioelectrochemical Systems
• Computational Fluid Dynamics

Background:

• Microbial electrochemical technologies (METs), especially microbial electrolysis cells (MECs), face scalability challenges due to mass transfer limitations.
• Efficient resource recovery from wastewater in MECs is often hindered by poor substrate transport to biofilms.

Purpose of the Study:

• To develop and validate a comprehensive computational fluid dynamics (CFD) model for a pilot-scale MEC (1 m³).
• To identify and quantify hydrodynamic and mass transfer limitations affecting substrate consumption and resource recovery in large-scale MECs.

Main Methods:

• A pilot-scale MEC (1 m³) was modeled using CFD, integrating fluid dynamics with bioelectrochemical substrate consumption.
• Simulations analyzed anolyte distribution, dead zones, and preferential flow paths under various operational conditions.
• The impact of hydraulic retention time (HRT), reaction kinetics, and diffusivity on MEC performance was evaluated.

Main Results:

• Laminar flow and poor flow distribution led to significant inefficiencies and low acetate removal.
• External mass transfer, not intrinsic reaction kinetics, predominantly governed reactor performance.
• Implementing a recirculation strategy enhanced acetate removal efficiency from 16% to 48%.

Conclusions:

• CFD modeling is a valuable tool for diagnosing transport limitations in large-scale MECs.
• Recirculation strategies can effectively mitigate mass transfer limitations without compromising volumetric capacity.
• This framework provides practical insights for optimizing MEC design and operation for enhanced resource recovery.