(418aa) Carbon Capture Using Carbonic Anhydrase-Displaying Escherichia coli in Biologically Active Foams

Carbon Capture Using Carbonic Anhydrase-Displaying Escherichia coli in Biologically Active
Foams
Stuart Watson, Zhenlin Han, Wei Wen Su, Eunsung Kan Department of Molecular Biosciences and Bioengineering University of Hawaii at Manoa
Honolulu, HI 96822
Abstract
In recent years, global warming as the result of greenhouse gas emissions, especially that of CO2, has become of great concern. Many technologies have been proposed and employed to capture post-combustion CO2 as governments worldwide have recognized the need to do so. Conventional methods such as absorption and adsorption have the problems of regeneration of spent solvents and media requiring additional energy input and expensive operating costs. For these reasons, the carbonic anhydrase enzyme (CA), which quickly catalyzes the conversion of CO2 into bicarbonate ion and a proton, has been studied for use in carbon capture and sequestration (CCS) technologies. This process would solve the limitations of current carbon capture technologies because it readily converts CO2 into environmentally friendly products at mild conditions. Furthermore, upon CO2 removal, the aqueous bicarbonate can be precipitated and separated as calcium carbonate (bio-mineral) as a value-added product. However, current CA-driven carbon capture remains problematic: 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 replaced over time as it gradually loses its activity. The major goals of this project are to employ genetically modified E. coli to continuously produce and display CA on their cell membranes and to use these bacteria in the Foam Bioreactor to capture and sequester CO2. The bacteria incubated in auto inducible media (AIM) have shown successful growth and enzyme expression as well as high activity and foaming capacity in the Foam Bioreactor. Because of the huge gas-to-liquid surface area in the Foam Bioreactor, the CO2 in gas phase was quickly transferred to many CA- displaying bacteria, allowing the CA to convert CO2 to bicarbonate ions and protons. Under ex situ pH control and an inlet stream of 2% CO2 at a cell concentration of 2.0 g/L, varying gas flow rates showed an optimum of 1 L/m with a removal efficiency (RE) of 50% and corresponding
elimination capacity (EC) of 1,980 gCO2/m3h. Investigations on cell concentration effects at fixed gas flow rate of 1 L/m and inlet CO2 showed increasing RE and EC as cell concentration increased from 0.015 g/L to 2.0 g/L, with an RE of 13 â?? 68%, respectively, and an EC of 660 â??
2,860 gCO2/m3h, respectively. Studies combining the cells with the tertiary amine solution,
MDEA, indicate the potential to combine this method of carbon capture as a means to refresh the
solution, rather than via conventional, energy-intensive methods. Furthermore, preliminary studies with in-line bicarbonate product removal show even higher removal of 90% and long- lasting steady states.