Engineers convert glycerin efficiently into ethanol, green chemicals via anaerobic fermentation

With biodiesel production in the EU and the US at an all-time high and a record number of new biodiesel plants under construction, the industry is facing an impending crisis over waste glycerin, the major byproduct of biodiesel production. New findings from Rice University suggest a possible answer in the form of the Escherichia Coli bacterium that anaerobically ferments glycerin into ethanol and valuable green chemicals. The efficiency of the conversion process is such that the researchers estimate operational costs to be 40% lower than first generation corn ethanol production.

The breakthrough fits nicely in the emerging concept of the integrated biorefinery that draws on an optimal cascading strategy in which waste-streams from one production process become feedstock for the creation of high value products based on other conversion processes.

For each tonne of biodiesel produced, around 100 kilograms of glycerin (glycerol) is obtained as a byproduct. The vast amount of glycerin that is now flooding the market has turned it from a valuable co-product into a 'waste' stream. This trend has prompted many researchers to find efficient and cost-effective ways to use the resource. So far they found that it can be turned into new types of biopolymers, bioplastic films, and green specialty chemicals such as propylene glycol. Others found glycerin makes for a suitable cattle and poultry feed or for the production of biogas.

Anaerobic fermentation
While some of these researchers are looking at traditional chemical processing - finding a way to catalyze reactions that break glycerin into other chemicals - others, including the Rice scientists, are focused on biological conversion. In biological conversion, researchers engineer a microorganism that can eat a specific chemical feedstock and excrete something useful. One of those biological conversion techniques is called anaerobic fermentation, and oxygen-free process widely used to produce biogas and some drugs. Anaerobic fermentation is the most economical and widely used process for biological conversion.

In a review article [*abstract] in the June issue of Current Opinion in Biotechnology, Ramon Gonzalez, William Akers Assistant Professor in Chemical and Biomolecular Engineering, points out that very few microorganisms are capable of digesting glycerin in such an oxygen-free environment. But they found a way to make the E. Coli bacterium do the job - efficiently and cost effectively.

We identified the metabolic processes and conditions that allow a known strain of E. coli to convert glycerin into ethanol. It's also very efficient. We estimate the operational costs to be about 40 percent less that those of producing ethanol from corn. - Ramon Gonzalez, lead author and William Akers Assistant Professor in Chemical and Biomolecular Engineering, Rice University

Glycerin glut
Gonzalez says the biodiesel industry's rapid growth has created a glycerin glut. The glut has forced glycerin producers like Dow Chemical and Procter and Gamble to shutter plants, and Gonzalez said some biodiesel producers are already unable to sell glycerin and instead must pay to dispose of it:
biofuels :: energy :: sustainability :: ethanol :: biodiesel :: glycerin :: byproduct :: anaerobic fermentation :: biorefinery :: bioeconomy ::

One pound of glycerin is produced for every 10 pounds of biodiesel. The biodiesel business has tight margins, and until recently, glycerin was a valuable commodity, one that producers counted on selling to ensure profitability. - Ramon Gonzalez, William Akers Assistant Professor in Chemical and Biomolecular Engineering

The discovery comes at a time when the chemical processing industry is increasingly finding bioprocessing to be a "greener," and sometimes cheaper, alternative to chemical processing.

"We are confident that our findings will enable the use of E. coli to anaerobically produce ethanol and other products from glycerin with higher yields and lower costs than can be obtained using common sugar-based feedstocks like glucose and xylose," Gonzalez concluded.

Biorefineries
The bioconversion technique is yet another example of the potential for integrated biorefineries that draw on an optimal cascading strategy in which waste-streams from different conversion processes become new feedstocks for other products. The implementation of biorefineries is aimed at co-producing as many high value products along with biofuels in a highly integrated way.

The report in Current Opinion in Biotechnology was co-authored by postdoctoral research associate Syed Shams Yazdani. Graduate students Yandi Dharmadi and Abhishek Murarka assisted with the research. Gonzalez's research is funded by the U.S. Department of Agriculture and the National Science Foundation.

Image: Because of its ubiquity, E. coli is frequently studied in microbiology and is the current "workhorse" in molecular biology. Its is widely used in genetic engineering and enzymes extracted from it are used industrial fermentation processes.

References:

Syed Shams Yazdania and Ramon Gonzaleza, "Anaerobic fermentation of glycerol: a path to economic viability for the biofuels industry" [*abstract], Current Opinion in Biotechnology, Volume 18, Issue 3, June 2007, Pages 213-219, doi:10.1016/j.copbio.2007.05.002

Eurekalert: Biotech breakthrough could end biodiesel's glycerin glut - June 26, 2007.