Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2011
Publication Date: 7/1/2011
Citation: Ashby, R.D., Solaiman, D., Strahan, G.D. 2011. Efficient utilization of crude glycerol as fermentation substrate in the synthesis of poly(3-hydroxybutyrate) biopolymers. Journal of the American Oil Chemists' Society. 88:949-959. Interpretive Summary: As focus shifts towards the production and utilization of biobased, renewable fuels, research is underway in a cost-cutting effort to ease production overhead and bring pricing more in line with petroleum-based fuels. One of the primary research focus points is in the development of innovative uses for any coproducts derived from biofuel synthesis. Biodiesel is one class of biofuel that has made worldwide inroads in recent years, however; biodiesel production results in a crude glycerol coproduct that represents approximately 10% of the total output, thus saturating the glycerol market. Many researchers are working to develop new uses for this crude glycerol coproduct by using it to chemically synthesize value-added products such as 1,2- and 1,3-propanediol (antifreeze applications) and glycerol-based polyesters (plastics) among others. Our research focus has been on crude glycerol as a fermentation substrate (food for microorganisms) for biological syntheses. In the present work, we demonstrated that crude glycerol (regardless of the specific source) can be used in fermentation applications to produce valuable, environmentally-friendly poly(3-hydroxybutyrate) (PHB) biopolymers that have potential in structural applications. We determined optimum fermentation conditions for polymer production and maximum glycerol utilization (limiting waste) as well as analyzed the specific physical properties of the resulting polymers. Thus, by using this crude glycerol coproduct we were able to demonstrate a new use for the coproduct plus produce a biopolymer that is known to possess properties comparable to polyethylene and polypropylene with the added benefit of biodegradability. By increasing the number of new outlets for coproducts (incl. crude glycerol) the value of these typical waste materials increases allowing biofuel producers an avenue to sell these coproducts and help offset the higher production costs of biobased fuels.
Technical Abstract: One refined and 2 crude glycerol samples were utilized to produce poly(3-hydroxybutyrate) (PHB) by Pseudomonas oleovorans NRRL B-14682. Fermentation conditions were determined to efficiently utilize glycerol while maintaining PHB yields. A batch culture protocol including 1% glycerol and an aeration rate of 3 standard liters per minute were best for PHB synthesis (ave. yield = 1.0 +/- 0.2 g/L at 48 h) and glycerol utilization which varied from 39% to 63% after 48 h depending on the crude glycerol sample. PHB molecular weights decreased as the MeOH media concentration increased. Refined glycerol resulted in PHB with number average molecular weights (Mn) of 314,000 g/mol which decreased by 17% and 90% as MeOH concentrations increased to <0.005% and 0.85%, respectively. Proton (1H) NMR demonstrated the presence of glycerol-based end-capping, which was confirmed by Doneshot proton diffusion experiments for “DOSY” analyses, which showed smaller diffusion constants (D) for the PHB synthesized from refined (D ~ 0.08 x 10exponent-10 m2/s) and crude glycerol (D ~ 0.3 x 10exponent-10 m2/s) than for free glycerol (D ~ 13 x 10exponent-10 m2/s) that was added to PHB synthesized from oleic acid prior to NMR analysis.