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Utilization of Carbonic Anhydrase-Displaying Escherichia coli in the Foam Bioreactor for Carbon Capture and Sequestration

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Item Summary

Title:Utilization of Carbonic Anhydrase-Displaying Escherichia coli in the Foam Bioreactor for Carbon Capture and Sequestration
Authors:Watson, Stuart
Keywords:Carbon capture
carbonic anhydrase
foam bioreactor
Date Issued:May 2015
Publisher:[Honolulu] : [University of Hawaii at Manoa], [May 2015]
Abstract:In recent years, global warming as the result of greenhouse gas emissions, especially carbon dioxide, has become of great concern. Many technologies have been proposed and employed to capture post-combustion CO2, but those in widest use have many disadvantages that make them inefficient. Physical and chemical absorption and adsorption as well as other physical separation methods all have the problems of regeneration of spent media and storage of captured CO2. Media regeneration often requires heating or pressure swings, which therefore require additional energy input. In addition to storage, captured CO2 is currently injected into the ground to react naturally with chemicals in a process similar to stalactite and stalagmite formation, or into the ocean, which increases its acidity. However, CO2 injection in either case can be an expensive process. For these and other reasons, the carbonic anhydrase enzyme (CA) has been studied for carbon capture and sequestration (CCS) because it catalyzes the conversion of CO2 and water into bicarbonate and a proton many times faster than the natural reaction. This process solves the media regeneration issue because it creates an environmentally safe, water-soluble product. Furthermore, the bicarbonate ion can be combined with calcium to form calcium carbonate, a valuable material in industry. However, current CA technology is expensive: the purified enzyme itself costs in the range of thousands of dollars per gram; the enzyme works best in slightly alkaline conditions, so some buffering capacity is necessary to combat the protons it generates; and CA must be continually replaced as it loses its activity over time.
The aim of this project, then, was to employ CA-producing bacteria in the recently developed foam bioreactor for continual enzyme production and increased mass transfer. Because of the very large gas-liquid interfacial area in the foam bioreactor, gaseous CO2 was quickly absorbed and converted by the CA to bicarbonate ions. When the CO2 removal was investigated at various conditions, very high removal rates and elimination capacities of CO2 were observed (up to 93% and 9570 g CO2 per m3 bioreactor h-1, at 24 s gas retention time, 4 gdw L-1 and 4% inlet CO2). These performances are superior to earlier reports of experimental bioreactors using CA for carbon capture. Additionally, a glucose-based auto inducible bacterial growth media (glucose AIM) was developed to enhance both growth and expression of lac operon-linked CA expression in genetically modified Escherichia coli. This media shows much higher enzymatic activity compared to the traditional lac operon expression method of induction via addition of isopropyl-β-D-1-thiogalactopyranoside (IPTG) to Luria-Bertani (LB) media. In addition, the glucose AIM does not experience excessive foaming during bacterial growth compared to LB or the recently developed LB-based auto inducible media (LB AIM) and is more cost effective as it is similar to a minimal media.
Description:M.S. University of Hawaii at Manoa 2015.
Includes bibliographical references.
Appears in Collections: M.S. - Molecular Biosciences and Bioengineering

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