The rapidly expanding market for biodiesel is dramatically altering the cost and availability of glycerol, as typical biodiesel production processes generate about 10 wt% glycerol. Biodiesel producers have little financial incentive to purify the crude glycerol, and since it contains methanol, crude glycerol is considered a hazardous waste. Therefore, it is critical that new and innovative processes for managing and utilizing the glycerol co-product be developed. In the longer term, as supplies continue to increase, glycerol will become a versatile building block chemical for the production of high value compounds within an integrated biorefinery.

The goal of this research is to investigate the value-added conversion of crude glycerol generated during biodiesel production using anaerobic fermentation. Pure cultures of Clostridium pasteurianum have previously been shown to produce significant amounts of butanol and 1,3-propanediol as well as some ethanol and lactic acid when utilizing purified glycerol as the sole substrate ^[1,2]. Butanol is of particular interest as a renewable biofuel, as it has a higher heating value, higher octane number, lower vapor pressure, and higher miscibility than ethanol, making butanol preferable to ethanol for blending with petroleum fuels.

This presentation will discuss the results of experiments evaluating growth and product formation of C. pasteurianum (ATCC^®6013^TM) utilizing biodiesel-derived crude glycerol as the sole carbon source. Crude glycerol containing approximately 5 g/L methanol and various salts was obtained from Alabama Biodiesel Corporation (Moundville, AL). Batch cultures were grown on purified glycerol and crude glycerol for comparison. Cultures utilizing crude glycerol have demonstrated significant growth and production of butanol, ethanol, and 1,3-PDO as well as complete substrate utilization. To the best of the authors' knowledge, this is the first report of butanol production from crude glycerol using this organism.

To date, this work has produced butanol yields up to 32 wt%. In contrast to previous work, these experiments did not produce lactic acid and did accumulate butyric acid. This presentation will present additional results regarding the yields of butanol, ethanol, and 1,3-PDO as well as present preliminary data for the extraction of products from the fermentation broth to produce a biofuel blend.

[1] Biebl, H. “Fermentation of Glycerol by Clostridium pasteurianum – Batch and Continuous Culture Studies.” Journal of Industrial Microbiology and Biotechnology. 2001. Vol. 27, 18-26.

[2] Dabrock, B.; Bahl, H.; Gottschalk, G. “Parameters Affecting Solvent Production by Clostridium pasteurianum.” Applied and Environmental Microbiology. 1992. Vol. 58, No. 4, 1233-1239.