Anthropogenic climate change is a critical issue that must be addressed with a systems approach. Greenhouse gas (GHG) emissions, like carbon dioxide (CO2), are key contributors to the climate crisis and originate from several different sources. Namely, the power industry is responsible for approximately 30% of U.S. CO2 emissions and 45% of global CO2 emissions. These emissions result from the combustion of carbon-based fuels, like coal and natural gas, and are emitted into the atmosphere in the form of flue gas. Being a large contributor of CO2 emissions has made the power industry the focus of research efforts to develop post-combustion carbon capture technologies. This work represents a comprehensive examination of microalgal cultivation and biomass utilization as methods for post-combustion carbon capture and replacement of fossil-dependent technologies and products. Optimized pilot-scale cultivation represents a sustainable post-combustion carbon capture technology with downstream economic value. An initial study of a 100 L photobioreactor (PBR) within a 100 MW power plant was conducted to optimize the long-term, continuous cultivation of the green microalgae Chlorella sorokiniana. The culture utilized flue gas as a source of CO2 and successfully operated continuously over a year long period. Insights from this study include the growth kinetics of C. sorokiniana, optimal cultivation conditions of the PBR, and an in-depth analysis of the microbial-microalgal assemblage throughout the study. The biomass produced during the 12-month study was stored and subsequently utilized to develop methods for cell disruption and protein recovery. This work investigated a mechanochemical method, using ball milling technology and chemically induced pH changes, to efficiently extract and recover microalgal proteins. The results of this study indicate that the mechanochemical method requires less energy than existing mechanical methods, while achieving similar levels of cell disruption.In addition to protein extraction and recovery, an alternate pathway for biomass utilization was explored. Microalgal biomass and microalgal proteins contain the foundational building blocks required for synthesis of chemicals like polyols. Polyols, used for polyurethane (PU) foam production, represent another value-added product that could provide the economic incentive to invest in microalgal cultivation for post-combustion carbon capture. Using biomass and recovered proteins as feedstocks, polyols were synthesized using a one-pot, two step method. Two microalgal polyols were selected based on their characterization and were evaluated using life cycle and techno-economic frameworks. The results elucidated the environmental and economic advantages when using microalgal biomass as an alternative to petrochemicals as a feedstock for polyol synthesis. Finally, this work evaluated a combined biological and chemical post-combustion carbon capture system using microalgal cultivation and a novel microalgal amino acid salt solution (MAASS). Life cycle and techno-economic frameworks were used to compare the MAASS to a standard amine-based solvent. The results of these assessments show that the MAASS capture system performs significantly better than an amine capture system, both in terms of environmental impacts and the cost of capture. This comprehensive collection of data and analysis represents advances in the field, as well as innovative methods and technologies that further demonstrate the viability of microalgal cultivation and biomass utilization for carbon capture from the power industry.
Read
