(291e) Fermentation of Biodiesel-Derived Crude Glycerol to Produce Value-Added Chemicals

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. As such, 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 and optimize the value-added conversion of crude glycerol generated during biodiesel production using anaerobic fermentation. In addition to producing 1,3-propanediol, acetic acid, and butyric acid, clostridia have been shown to produce up to 8.8 g/L lactic acid and 17 g/L butanol during the anaerobic fermentation of glycerol [1,2]. The most influential parameters affecting this fermentation are nutrient/trace metal supplementation, pH, and substrate composition and concentration. Unfortunately, none of these parameters have been thoroughly investigated or quantified with respect to production of lactic acid and butanol.

Biomass samples were collected from anaerobic digesters at both a biodiesel production facility and a municipal wastewater treatment facility. Samples were pre-treated to select for clostridia and inactivate competing organisms such as methanogens. Acclimation experiments were conducted in 500 mL batch reactor systems under conditions of excess nutrients and trace metals. Efforts have resulted in successful acclimation of an enriched culture of clostridia capable of using crude glycerol obtained from a local biodiesel facility as the sole carbon source. These cultures exhibit good glycerol utilization and have produced notable amounts of lactic acid, 1,3-propanediol, acetic acid and butyric acid under un-optimized conditions. Continuing efforts are focused on improving lactic acid and butanol production as well as glycerol utilization by optimizing the nutrient solution/trace metal concentration and composition. Experiments are evaluating the effect of key trace metals, including Fe, Co, Ni, and Mo, to determine the appropriate concentrations for increased production of lactic acid and butanol. Additional experiments are investigating the effect of providing excess macro-nutrients, specifically nitrogen and phosphorus, to improve crude glycerol utilization and product formation. The progress of the fermentation is monitored by measuring CO2 production (as pressure) as well as the pH of the fermentation broth. Liquid samples are analyzed for glycerol, lactic acid, butanol, and other products using HPLC. This presentation will quantify and compare product formation and glycerol utilization over a range of nutrient solution formulations and identify those formulations that favor lactic acid and/or butanol production.

[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.