Researchers at Rice University claim they’ve discovered a way to make ethanol from the waste glycerol (syn: glycerin) produced in biodiesel manufacturing. If true, it could be the biggest breakthrough in biodiesel production in years.

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

Biodiesel is made by splitting fat molecules into smaller pieces and draining off the thicker components, better known as glycerin. Anyone familiar with homemade biodiesel knows what glycerin is: a sticky, nasty mess that’s also a disposal headache. Waste glycerin is no small problem for the commercial biodiesel industry either, since 10 lbs. of biodiesel produces 1 lb. of glycerin, and what was once a valuable commodity now frequently entails a disposal cost. In the short span of two years, glycerin commodity prices have decreased by a factor of 10, while overall production has increased by 400%. Finding a solution to the waste problem has been a top priority for some time now (check out the Glycerol Challenge):

Researchers across the globe are racing to find ways to turn waste glycerin into profit. While some are looking at traditional chemical processing — finding a way to catalyze reactions that break glycerin into other chemicals — others, including Gonzalez, are focuse on biological conversion. In biological conversion, researchers engineer a microorganism that can eat a specific chemical feedstock and excrete something useful. Many drugs are made this way, and the chemical processing industry is increasingly finding bioprocessing t be a “greener,” and sometimes cheaper, alternative to chemical processing.”

Researchers have been ‘racing’ over this issue for some time, but until now the best use of waste glycerin I’d heard of is dust suppression on country roads. But biodiesel producers are keen on finding valuable co-products that can pad their very slim profit margins ($0.079 per gallon of biodiesel according to one source).

Skeptical? By now most of us in the renewable energy crowd have to see it to believe it. Anyone familiar with the waste product produced from even the cleanest-looking waste vegetable oil would be hard-pressed to imagine it successfully converted to ethanol. If feasible, however, it could be the next big thing for commercial biodiesel producers everywhere:

“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 cost than can be obtained using common sugar-based feedstocks like glucose and xylose,” Gonzalez said.”

These statements released by Rice University stem from a scientific review paper entitled Anaerobic fermentation of glycerol: a path to economic viability for the biofuels industry. This scientific review paper is not available without subscription, but here are a few excerpts:

“The implementation of biorefineries has been proposed as a means to increase the economic viability of the biofuels industry [9]. In its ‘conventional’ form, a biorefinery would make use of a fraction of the feedstock (e.g. a portion of sugars or oils) to co-produce a higher value, small-market chemical along with the biofuel(s). The higher revenue from the co-product, which benefits itself from the economies of scale available in a large biofuels plant, would improve the economics of biofuel production. A more economically viable model for a biorefinery, however, should consider the use of byproducts or waste streams generated during the production of the biofuel. Glycerol-rich streams generated by the biofuels industry (Figure 1a) have the potential to be used in this context. This review focuses on the anaerobic conversion of crude glycerol into higher value products as a means to improve the economic viability of the biofuels industry.”

“For example, an analysis of the feedstock and processing costs in the production of biodiesel from soybean oil yields a gross processing margin of about $0.079 per gallon of biodiesel (including a glycerol credit of $0.021, but excluding any interest expense, tax credits or fixed costs) (04/11/2007: www.thejacobsen.com). Essentially, if 2004 glycerol prices (Figure 1b) were still valid, the glycerol revenues by themselves would amount to about three times the current gross processing margin (i.e. crude glycerol at $0.25/ lb  0.85 lb/gal would result in a glycerin credit of $0.21). Clearly, the development of processes to convert crude glycerol into higher value products is both an urgent need and a ‘target of opportunity’ for the development of biorefineries. Such technologies could be readily integrated into existing biodiesel facilities, thus establishing true biorefineries and revolutionizing the biodiesel industry by dramatically improving its economics. Moreover, waste streams containing high levels of glycerol are generated in almost every industry that uses animal fats or vegetable oils as starting material (Figure 1a). For example, the oleochemical industry generates waste streams containing 55–90% glycerol [14]. Such glycerol surplus will not only result in a further reduction in prices, but the disposal of these streams will become a major issue [12].”

“At current prices (2.5 cents/lb), glycerol is very competitive with sugars used in the production of chemicals and fuels via microbial fermentation. Given the highly reduced nature of carbon atoms in glycerol, additional advantages can be realized by using glycerol instead of sugars. For example, conversion of glycerol into the glycolytic intermediates
phosphoenolpyruvate (PEP) or pyruvate generates twice theamount of reducing equivalents produced by the metabolism of glucose or xylose (Figure 2). Fermentative metabolism would then enable higher yield of fuels and reduced chemicals from glycerol compared with those obtained from common sugars such as glucose or xylose.”

Biotech breakthrough could end biodiesel’s glycerin glut (June 19, 2007)
Syed Shams Yazdani and Ramon Gonzalez. Anaerobic fermentation of glycerol: a path to economic viability for the biofuels industry. Current Opinion in Biotechnology: Volume 18, Issue 3, June 2007, Pages 213-219

Photo Credit: Rice University