Browsing by Author "Hollis, W. Kirk"

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Microbially enhanced carbonate mineralization and the geologic containment of CO2
(2008) Mitchell, Andrew C.; Phillips, Adrienne J.; Kaszuba, John P.; Hollis, W. Kirk; Cunningham, Alfred B.; Gerlach, Robin
Geologic sequestration of CO2 involves injection into deep underground formations including oil beds, un-minable coal seams, and saline aquifers with temperature and pressure conditions such that CO2 will likely be in the supercritical state. Supercritical CO2 injection into the receiving formation will result in elevated pressure in the region surrounding the point of injection, and may result in an upward hydrodynamic pressure gradient and associated â€œleakageâ€ of supercritical to gaseous CO2. Therefore mechanisms to reduce leakage and to mineralize CO2 in a solid form are extremely advantageous for the long-term geologic containment of CO2.This paper will focus on microbially-based strategies for controlling leakage and sequestrating supercritical CO2 during geologic injection. We will examine the concept of using engineered microbial barriers (Cunningham et al., in review; Mitchell et al., in review) which are capable of precipitating calcium carbonate (Mitchell and Ferris, 2005; 2006) under high-pressure subsurface conditions. These â€œbiomineralization barriersâ€ may provide a method for plugging preferential flow pathways in the vicinity of CO2 injection, thereby reducing the potential for unwanted upward migration of CO2, as well as mineralizing injected CO2. A summary of experiments investigating biofilm and associated calcium carbonate formation in porous media using a unique high pressure (8.9 MPa), moderate temperature (â‰¥ 32 Â°C) flow reactor will be presented, and the potential for biomineralization enhanced CO2 sequestration discussed.
Resilience of planktonic and biofilm cultures to supercritical CO2
(2008-12) Mitchell, Andrew C.; Phillips, Adrienne J.; Hamilton, Martin A.; Gerlach, Robin; Hollis, W. Kirk; Kaszuba, John P.; Cunningham, Alfred B.
Supercritical CO2 has been shown to act as a disinfectant against microorganisms. These organisms have most often been tested in vegetative or spore form. Since biofilm organisms are typically more resilient to physical, chemical, and biological stresses than the same organisms in planktonic form, they are often considered more difficult to eradicate. It is therefore hypothesized that supercritical CO2 (SC–CO2) induced inactivation of biofilm organisms would be less effective than against planktonic (suspended) growth cultures of the same organism. Six-day old biofilm cultures as well as suspended planktonic cultures of Bacillus mojavensis were exposed to flowing SC–CO2 at 136 atm and 35 ◦C for 19 min and slowly depressurized after treatment. After SC–CO2 exposure, B. mojavensis samples were analyzed for total and viable cells. Suspended cultures revealed a 3 log10 reduction while biofilm cultures showed a 1 log10 reduction in viable cell numbers. These data demonstrate that biofilm cultures of B. mojavensis are more resilient to SC–CO2 than suspended planktonic communities. It is hypothesized that the small reduction in the viability of biofilm microorganisms reflects the protective effects of extracellular polymeric substances (EPS) which make up the biofilm matrix, which offer mass transport resistance, a large surface area, and a number of functional groups for interaction with and immobilization of CO2. The resistance of biofilm suggests that higher pressures, longer durations of SC–CO2 exposure, and a quicker depressurization rate may be required to eradicate biofilms during the sterilization of heat-sensitive materials in medical and industrial applications. However, the observed resilience of biofilms to SC–CO2 is particularly promising for the prospective application of subsurface biofilms in the subsurface geologic sequestration of CO2.