Beneficial Re-use of Carbon Emissions from Coal-fired Power Plants using Microalgae

Utilization of CO2 as a raw material for the production of biological-based products represents a promising alternative to other CO2 utilization technologies. Biological-based products benefit environmentally from the use of waste or atmospheric carbon given that the resulting products are intrinsically constructed with recycled carbon, whereas traditional products are typically generated from stored carbon resources that are eventually released to the atmosphere at the end of life. In order to develop a cost-effective process that can productively convert CO2 from coal-fired flue gas to value-added products, this project will focus on microalgae-based CO2 capture, with conversion of the resulting algal biomass to bioplastics and fuels. Specifically, the project aims to decrease the cost of algae cultivation (and hence CO2 capture) via a combined photobioreactor/pond cultivation strategy, while developing a utilization strategy which aims to extract maximum value from the produced algal biomass. To this end, the University of Kentucky (UK), Colorado State University (CSU) and the University of Delaware (UD), in collaboration with our industrial partner ALGIX LLC, propose to address three key areas, viz.: (i) critical commercial-scale development barriers pertaining to algae cultivation, namely, the capital cost of the cultivation system and the maintenance of productive cultures; (ii) development of sustainable, large-scale applications for the produced biomass, while maximizing the potential revenue stream; and (iii) assessment of the economics and greenhouse gas implications of this approach to CO2 utilization. Scenedesmus acutus algae (UTEX B72) will be autotrophically cultured in a system combining an innovative "cyclic flow" photobioreactor (PBR) with conventional raceway ponds, the algae being harvested and dewatered using technology previously developed at UK based on flocculation/sedimentation/filtration. By adopting a dual PBR/pond approach, we aim to combine the best features of both. Specifically, the PBR will be used to produce a concentrated (~1 g/L) Scenedesmus monoculture which will be used to inoculate the ponds at a concentration (~0.2 g/L) which is sufficiently high as to minimize growth lag time and ensure that the Scenedesmus can effectively out-compete invasive organisms. As algal biomass is harvested from the ponds (~0.8 g/L), fresh Scenedesmus will be added from the PBR. This "over-seeding" will ensure that a viable culture is always maintained in the ponds and that Scenedesmus is always the dominant organism. In this manner we aim to maximize pond productivity by minimizing pond crashes, and hence downtime, due to invasive organisms. In tandem, a biomass fractionation strategy will be developed which produces a protein-rich feedstock for the production of algal-based bioplastics, as well as a lipid feedstock for the production of fuels and an aqueous carbohydrate stream which can be utilized as a feedstock for chemicals and /or fuels. Algal biomass will be subjected to lipid and carbohydrate extraction at UK, the protein-rich residue being trialed at ALGIX for the production of bioplastics. The ultimate deliverable from this project will be the design of an algae-based system tailored to the conversion of CO2 emissions from coal-fired power plants to fuels and bioplastics, thereby contributing to the mitigation of CO2 in areas where geologic storage may not be a viable solution.