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Microbial Fermentation of Glycerol for the Production of Ethanol

Ashutosh Gupta, Chemical and Biomolecular Engineering, Rice University, MS-362, 6100 S Main St, Rice University, Houston, TX 77005 and Ramon Gonzalez, Departments of Chemical & Biomolecular Engineering and Bioengineering, Rice University, MS-362, P.O. Box 1892, Houston, TX 77251-1892.

Microbial fermentation of glycerol for the efficient production of ethanol

Unprecedented increase in crude oil prices in recent times has led to worldwide increase in the production of bio-based chemicals and fuels. Glycerol is an inevitable byproduct in the production of biodiesel. Its value for biodiesel manufactures has changed dramatically from being a valuable co-product to a waste product in last few years. This has created an urgent need to find new platforms for the production of value added products from glycerol.

We have recently identified several microorganisms, including E. coli and other enteric bacteria, which can efficiently ferment glycerol if cultivated under appropriate culture conditions. I all cases ethanol was found to be the main product of glycerol fermentation. These organisms have significant industrial advantages for glycerol utilization in terms of yield, productivity, low nutritional requirements, and ability to grow in presence/absence of oxygen.

In this work, we present the effect of pH on the fermentation of glycerol by these microorganisms in batch cultures. We show our result that changes in pH from acidic to basic medium, results in a transition from glycerol fermenting to glycerol non-fermenting behavior. We also report the effect of changes in media composition on glycerol utilization and growth. Effects of changing headspace environment from inert to carbon dioxide are also presented. Fermentation in these microorganisms is enabled by the production of 1,2 propanediol, which results in the consumption of excess reducing equivalents generated by the synthesis of cell biomass from glycerol.