Hollow Fiber Membrane (HFM) Facilitated CO₂ Delivery to a Cyanobacteria Layer for Biofuel Production

Photosynthetic bacteria have been shown to be advantageous organisms for biofuel production due to high CO₂ fixation efficiencies, fast growth rates, and lower water requirements. Recently, cyanobacteria been metabolically engineered to efficiently secrete their products into a surrounding solution. This has the advantage of potentially eliminating the requirement to harvest and post-process the organisms in order to extract a biofuel, which is one of the most energy and water expensive processes in most biodiesel production strategies. Lagging behind the development of these organisms however has been the development of new photobioreactor (PBR) strategies that can efficiently delivery light and inorganic carbon to the bacteria while extracting the secreted product and O₂ from the solution phase. Hollow fiber membranes (HFMs) are a method for bubble-less gas exchange that has been shown to be effective at enhancing mass transfer in applications such as wastewater and landfill treatment. HFM technology could be used to overcome the mass transport challenges associated with photobioreactors. HFM modules have been used to increase mass transfer of CO₂ to the bulk media in bench scale PBRs; however, the use of HFM fibers as both a mean to exchange and deliver a gas phase throughout a PBR has not been explored. We have characterized the passive transport along a single fiber in a miniature reactor in previous work. Here we extend our work to arrays of HFM fibers. We performed a range of experiments to characterize bacteria growth rate and distribution as a function fiber spacing and active transport through the fibers, and report optimized values for these variables.