Batch and Continuous Flow Column Studies of Methane Consumption and Methanol Production by Methylosinus Trichosporium OB3b and Methylomicrobium Buryatense 5GB1 Immobilized In Ca-Alginate and Agarose Hydrogels Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4j03d309t

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  • Two methanotrophs, M. trichosporium OB3b and M. buryatense 5GB1, were encapsulated using two methods to investigate the potential of methane conversion for biofuel production. Ca-alginate and low melt agarose were used to immobilize the methanotrophs for batch and continuous flow column testing. Varying protein concentrations, residence times, and immobilization methods were compared for methane consumption and product formation. An integrated Monod model was used in conjunction with batch experiments to derive kinetic parameters for each culture type, for suspended and immobilized forms. Suspended OB3b showed an average maximum substrate utilization rate, Kmax, of 0.0089 mg CH₄/mg protein/min and a half saturation coefficient, Ks, of 2.3 mg CH₄/L. Suspended 5GB1 exhibited a Kmax of 0.0093 mg CH₄/mg protein/min and K[subscript s] of 1.9 mg CH₄/L. OB3b immobilized in agarose and externally cross-linked alginate gel beads showed equivalent levels of methane consumption when immobilization methods were directly compared and the K[subscript s] values were slightly higher indicating mass transfer limitations into the films. Monod kinetic parameters were applied in conjunction with a biofilm diffusion-kinetics model developed by Rittmann and McCarty to simulate methane consumption in a constant mixed biofilm reactor (CMBR). The model provided a good fit to activity trends seen in continuous flow column tests such as higher extents of methane removal with respect to increasing biomass concentration. OB3b was investigated for the direct production of methanol through chemical inhibition of the methanol dehydrogenase enzyme. Cyclopropane and cyclopropanol were used as inhibitors in batch and column reactors with immobilized cultures. Results showed initial concentrations of methanol production up to 0.12 mg methanol/L in a packed column reactor. Two consecutive cycles of inhibition were conducted to investigate re-inhibition of OB3b for long term methanol production. The two inhibition cycles produced equal levels of methanol and maintained constant levels of methane consumption, indicating OB3b can be effectively re-inhibited. Maximum levels of methanol conversion efficiency ranged from 13-17% for the batch reactor inhibited with cyclopropane exposure and 75-140% conversion efficiency for the continuous flow column inhibited directly with biologically produced cyclopropanol.
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