Using wavy laminar flow for continuous microbial gas processing
The process of carbon capture, utilization and storage provides an appealing method to lower emissions from various sources. Microorganisms have been widely explored credit to their capability to assimilate gaseous carbon and convert it to useful products. Unfortunately, large volumes of natural gas, digester gas, and waste carbon gases cannot be recycled by existing microbial or algal bioreactor systems due to the high energy cost involved for gas-liquid mass transfer, demand for large quantities of water for traditional bioprocesses, and the very slow specific rates of carbon assimilation. As such, a more rapid and energy efficient method for recycling carbon gases using live microorganisms is needed. Ideally, efficient recycling of gaseous carbon to chemicals using highly concentrated immobilized microorganisms as biocomposite materials is possible with reduced water use and power input for gas-liquid mass transfer using a falling film bioreactor (FFBR). In a FFBR, a wavy laminar liquid film (Re < 200) descends over a cylindrical paper biocatalyst to provide efficient gas-liquid mass transfer without bubbles, provide hydration and nutrients to the cells, and remove secreted liquid products. Paper roughness has previously been shown to enhance gas-liquid mass transfer.
The idea of using papers to grow or immobilize live cells offers outstanding properties environmentally, technically and even economically. More so, paper has recently been reported to enhance the rate of CO2 absorption by algae in an illuminated spinning disk bioreactor. Regardless, there is more to be explored regarding the applicability of paper in CO2 capture processes and systems. On this account, researchers from the North Carolina State University: Dr. Ryan Barton, Ms. Kelly VanTreeck, Mr. Christopher Duran, Dr. Mark Schulte and led by Professor Michael C. Flickinger investigated the use of a new model paper biocomposite support. Their goal was to demonstrate enhance gas-liquid mass transfer of a FFBR. Their work and previous CFD modeling work are both published in the research journal, Chemical Engineering Science.
In their proof-of-concept work, two prototype falling film gas-absorbing bioreactors (~1 m long FFBR, ~0.1 m long mFFBR) were investigated using a chromatography paper biocatalyst support in contact with a continuously falling thin wavy degassed water film to both minimize power input (wavy laminar flow regime; Re < 200) to achieve high kLa and to reduce water. Specifically, the FFBR was evaluated based on liquid flow properties, liquid film thicknesses, and resulting gas-liquid transfer of oxygen to the flowing liquid phase which was measured as kLa. More so, prototype flow distributors for the FFBR were generated by 3D printing. This system was technically challenging because it was designed to safely process mixtures of methane in air using engineered microbes.
The authors reported that both the FFBR achieved very high kLa values which were comparable to gas-liquid mass transfer rates for falling film chemical reactors. Further, the prototype was reported to possess various advantages; i.e. it was beneficial for gas-absorbing microorganisms that are able to be immobilized; e.g. via biocomposite biocatalyst, and engineered to secrete products (either gas or liquid).
In summary, Professor Michael Flickinger and his bioprocess intensification (BPI) research team demonstrated the gas-liquid mass transfer properties of a prototype FFBR for continuous large-scale bioprocessing of gaseous carbon to chemicals with reduced water and power input. The prototype bioreactor showed reduced amounts of shear stress to cells and the potential for increased product titers and reduced recovery costs as a result of significantly reduced liquid volume. In a statement to Advances in Engineering, the authors highlighted that by using their new FFBR BPI approach to enhance gas absorption rate in combination with non-growing paper biocomposite biocatalysts will enable a paradigm shift toward intensifying gas uptake rates by the microorganisms as well as incentivize engineering of microorganisms that absorb gases and secrete products in the absence of growth.
Professor Michael Flickinger’s BPI research group is also studying the impact of their innovative biocomposite technologies to not only recycle gaseous carbon but also microbial biosolar energy driven thin film biocomposite processes that utilize minimal water and power to convert wastes to useful products.
Ryan R. Barton, Kelly E. VanTreeck, Christopher J. Duran, Mark J. Schulte, Michael C. Flickinger. A falling film bioreactor (FFBR) for generating effective gas-to-liquid mass transfer using wavy laminar flow for continuous microbial gas processing. Chemical Engineering Science, volume 219 (2020) 115592.
Also recommended paper by Yuxiu Chen et al., Introducing porosity in colloidal biocatiings to increase bacterial viability. BioMacromolecules (2020). Authors discussed biocoatings and its potential to change the entire coating industry by including the biotechnology of live cells in reactive coatings.