Design and validation of a new flat-sheet membrane bioreactor system for bioprocessing research requiring very low gas fluxes

Precise and consistent gas dosing at trace levels remains a significant challenge in bioprocessing and biotechnology research. This study introduces a novel flat-sheet membrane bioreactor for controlled gas delivery without bubble formation. The system relies on gas diffusion mediated by interchangeable membrane cassettes and incorporates mechanical stirring near the membrane surface to promote gas dispersal and mitigate biofouling spanning long operating periods. Comprehensive characterization of mass transfer properties using oxygen gas as a test case revealed that the volumetric mass transfer coefficient (KLa) remained stable under varying operational conditions, including gas partial pressure, back pressure, and total gas flow rate. The maximum oxygen flux under specific operational conditions flexibly ranged from 15.9E-03 {+/-} 6.3E-03 mol{middle dot}min-1 to 1.08 {+/-} 0.17 mol{middle dot}min-1 for various porous membranes and from 23.3E-03 {+/-} 3.5E-03 mol{middle dot}min-1 to 0.161 {+/-} 0.044 mol{middle dot}min-1 for the non-porous membranes, indicating the bioreactor can serve as an experimental platform for a variety of applications. A biological validation study using starch-containing wastewater demonstrated the feasibility of continuous microaerobic oxygen dosing, achieving reproducible performance and maintaining stable operation over 320 days. These findings highlight the potential of the developed system as a reliable experimental platform for investigating bioprocesses dependent on trace gas supply. Future improvements should focus on scaling up the system, addressing porous membrane wetting, and expanding its applicability to other gases and bioprocessing applications.