Submitted to: Journal of Environment and Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2004
Publication Date: 7/1/2004
Citation: Ashby, R.D., Solaiman, D., Foglia, T.A. 2004. Bacterial poly(hydroxyalkanoate) polymer production from the biodiesel co-product stream. Journal of Environment and Polymers. 12(3):105-112. Interpretive Summary: Biodiesel is presently being studied as an alternative to petro-diesel. It is derived from the chemical modification of animal fats and vegetable oils and is steadily gaining acceptance because of its fuel properties and reduced emissions. In fact, within the next 8-10 years biodiesel markets are predicted to increase by as much as 1000 percent and, while this increase may be beneficial for the environment, it will also result in increased amounts of a co-product stream that is rich in glycerol. Glycerol is a large volume chemical that is commonly used in oral-care products, tobacco, cosmetics and food and beverages. However, in order for glycerol from the co-product stream of biodiesel production (CSBP) to be used in these applications it must be separated from the other components of the CSBP, which may be a costly process. Poly(hydroxyalkanoates) (PHAs) are a class of 'environmentally friendly' bacterial polymers that can be classified as either rigid or elastomeric based on their origin and chemical composition. PHAs have attracted a lot of interest because their properties can closely approximate those from petrochemical-based polymers, with the added advantage of biodegradability. Historically, however, the drawback to PHA use has been the cost to produce these polymers. In this study we took advantage of the ability of two different bacterial strains to grow and produce two distinct PHA polymers (one rigid and one elastomeric) from CSBP material. In so doing, we established a use for CSBP as a feedstock for PHA production without the need to separate the components and, at the same time, decreased the cost of producing PHA polymers, thus expanding their market potential.
Technical Abstract: A co-product stream from soy-based biodiesel production (CSBP) containing glycerol, fatty acid soaps, and residual fatty acid methyl esters (FAME) was utilized as a fermentation feedstock for the bacterial synthesis of poly(3-hydroxybutyrate) (PHB) and medium-chain-length poly(hydroxyalkanoate) (mcl-PHA) polymers. Pseudomonas oleovorans NRRL B-14682 and P. corrugata 388 grew and synthesized PHB and mcl-PHA, respectively, when cultivated in up to 5 percent (w/v) CSBP. In shake flask culture, P. oleovorans grew to 1.3 +/- 0.1 g/L (PHA cellular productivity = 13-27 percent of the bacterial cell dry weight; CDW) regardless of the initial CSBP concentration, whereas P. corrugata reached maximum cell yields of 2.1 g/L at 1 percent CSBP, which tapered off to 1.7 g/L as the CSBP media concentration was increased to 5 percent (maximum PHA cellular productivity = 42 percent of the CDW at 3 percent CSBP). While P. oleovorans synthesized PHB from CSBP, P. corrugata produced mcl-PHA consisting primarily of 3-hydroxyoctanoic acid (C8:0; 39 +/- 2 mol percent), 3-hydroxydecanoic acid (C10:0; 26 +/- 2 mol percent) and 3 hydroxytetradecadienoic acid (C14:2; 15 +/- 1 mol percent). The molar mass (Mn) of the PHB polymer decreased by 53 percent as the initial CSBP culture concentration was increased from 1 percent to 5 percent (w/v). In contrast, the Mn of the mcl-PHA polymer produced by P. corrugata remained constant over the range of CSBP concentrations used.