A team of researchers at Iowa State University (ISU; Ames; www.iastate.edu) have developed a new bioreactor concept that streamlines production of value-added bioproducts at smaller scales by integrating three process steps (fermentation, product extraction and separation) into a single, compact unit. The reactor is based on the Taylor vortex principle, wherein media flows between two concentric cylinders that are precisely rotated to create special turbulence patterns. “Our continuous Taylor vortex bioreactor consists of a vertical rotating inner cylinder, an outer stationary concentric cylinder and a reaction medium (fermentation broth) occupying the annular region between the two cylinders. At sufficiently high inner-cylinder rotation speeds, toroidal flow patterns — known as Taylor vortices — arise. These structures enable fast azimuthal and radial mixing, as well as relatively uniform turbulence dissipation rates throughout the reactor and very fast interphase mass transport for multiphase flow,” explains Dennis Vigil, professor of chemical and biological engineering at ISU. When compared to traditional bioreactors, ISU’s reactor supports faster fermentation at much lower aeration rates for the same titer and yield. This is due to the accelerated interphase transport that is facilitated by Taylor vortices.
“The reactor can also be operated continuously: target products can be extracted periodically and separated from the fermentation broth by using centrifugal separation, achieved by passing the emulsion through the inside of the rotating inner cylinder (by making it hollow). The wall-driven annular flow provides a hydrodynamic environment that is more homogeneous than in many commonly used bioreactors, such as stirred tanks, bubble columns and airlift reactors,” adds Vigil. This level of homogeneity serves to improve microorganism performance, further improving titer and yield.
With funding from BioMADE, a Department of Defense-sponsored Manufacturing Innovation Institute focused on bioindustrial manufacturing, the team has demonstrated fermentation in a 14-L Taylor vortex bioreactor device (scaling up from a 1-L prototype device) and developed scaleup criteria, which will be validated over a larger range of reactor sizes and microbial hosts. The technology is expected to be most impactful for high-value, low-volume products, where conventional industrial-scale fermentation processes do not make economic sense. And while Taylor vortex devices have been employed in industry for such operations as liquid-liquid extraction and oil-water separations, there have been limited attempts to adapt the technology for industrial biomanufacturing thus far. The new bioreactor’s versatility, modularity and ability to support a wide range of microbial hosts make it promising as an economical manufacturing route for many high-value bioproducts.
“Even at scales smaller than a conventional bioreactor, the Taylor vortex bioreactor has the potential to produce significant quantities of high-value materials at low cost. With its ability to ferment and separate in a single piece of equipment — and its low power draw —the reactor could ultimately serve as the ‘heart’ of a deployable manufacturing system,” adds David Nathan, a technical program director at BioMADE.