Airlift Taylor Flow bioreactors as a novel platform to enhance H2-assisted CO2 bioconversion processes

The microbial valorization of CO 2 requires the development of novel bioreactor configurations capable of ensuring a cost-effective gas-liquid mass transfer. This study presents the design, characterization and performance evaluation of a novel Airlift Taylor Flow Reactor (ATFR), which integrates the gas-induced liquid recirculation of airlift systems, with the high gas-liquid mass transfer potential of Taylor flow in multicapillary systems. The liquid recirculation flow in the downcomer was quantified using a colour tracer method, and the volumetric oxygen mass transfer coefficient (k L a) was determined via the sulphite oxidation method, both with and without forced recirculation. The results showed that the implementation of forced mechanical recirculation via a centrifugal pump negatively impacted the total liquid recirculation and k L a. A maximum k L a of 891 ± 23 h −1 was achieved at a gas flow rate of 60 L min −1 , representing a 75 % increase compared to the same condition with external forced liquid recirculation. The autotrophic growth of Cupriavidus necator showed a direct correlation with k L a, with a 171 % increase in maximum cell concentration and a 67 % increase in the specific growth rate when k L a increased from 183 to 364 h −1 . These findings highlight the potential of the ATFR as a promising platform for gas-liquid mass transfer-limited processes, particularly in systems bioconverting poorly soluble gases such as H 2 , CH 4 , CO and O 2 . • A novel Airlift Taylor Flow Reactor was designed for CO 2 bioconversion processes • External liquid recirculation decreased the downcomer liquid velocity and k L a • A maximum k L a of 891 h −1 was reached, among the highest in non-stirred systems • ATFR reached 18 folds higher k L a than conventional airlift reactors at the same P/V • C. necator biomass concentration increased by 171 % as k L a rose from 183 to 364 h −1