Mass Transfer, Gas Holdup, and Kinetic Models of Batch and Continuous Fermentation in a Novel Rectangular Dynamic Membrane Airlift Bioreactor

Compared with conventional cylinder airlift bioreactors (CCABs) that produce coarse bubbles, a novel rectangular dynamic membrane airlift bioreactor (RDMAB) developed in our lab produces fine bubbles to enhance the volumetric oxygen mass transfer coefficient (k_La) and gas holdup, as well as improve the bioprocess in a bioreactor. In this study, we compared mass transfer, gas holdup, and batch and continuous fermentation for RNA production in CCAB and RDMAB. In addition, unstructured kinetic models for microbial growth, substrate utilization, and RNA formation were established. In batch fermentation, biomass, RNA yield, and substrate utilization in the RDMAB were higher than those in the CCAB, which indicates that dynamic membrane aeration produced a high k_La by fine bubbles; a higher k_La is more beneficial to aerobic fermentation. The starting time of continuous fermentation in the RDMAB was 20 h earlier than that in the CCAB, which greatly improved the biological process. During continuous fermentation, maintaining the same dissolved oxygen level and a constant dilution rate, the biomass accumulation and RNA concentration in the RDMAB were 9.71% and 11.15% higher than those in the CCAB, respectively. Finally, the dilution rate of RDMAB was 16.7% higher than that of CCAB during continuous fermentation while maintaining the same air aeration. In summary, RDMAB is more suitable for continuous fermentation processes. Developing new aeration and structural geometry in airlift bioreactors to enhance k_La and gas holdup is becoming increasingly important to improve bioprocesses in a bioreactor.