Fuel from Fallow

Biologists seek to make energy from biodiesel waste.


After Rudolf Diesel debuted his peanut oil engine at the World’s Fair in 1900, it wasn’t uncommon to see hemp, tallow, and corn oil used for energy. But when fossil fuel prices dropped in the 1940s, biodiesel—a renewable fuel source made by separating methyl esters from glycerin in vegetable oil—fell into obscurity, and petroleum diesel became the norm.

As social pressures mount in favor of moving beyond a fossil fuel economy, and already high gas prices continue to climb, it’s perhaps no surprise that biodiesel production is on a 10-year upswing. As a testament to the field’s growth, the fuel was spotlighted at the 32nd Symposium on Biotechnology for Fuels and Chemicals held last April in Clearwater Beach, Fla. And taking center stage—projects that transform a sticky biodiesel waste product into a valuable commodity.

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For every 100 kilograms of biodiesel produced, 10 kilograms of oily, molasses-colored goop are left behind. It’s called crude glycerin by the biodiesel industry, and glycerol by academics, but Rice University bioengineer Ramon Gonzalez says “a rose is a rose” when it comes to the byproduct’s commercial potential—namely, serving as an additional source of energy and fuel.

“By making ethanol from a waste product, we can squeeze more biofuel from each batch of biodiesel.” —Ramon Gonzalez

Gonzalez uses E. coli to ferment the waste into ethanol, which can be added to biodiesel or gasoline to stretch each gallon a little further. Others are experimenting with bacteria that break down glycerol into butanol—another energy-boosting fuel additive. “By making ethanol from a waste product, we can squeeze more biofuel from each batch of biodiesel,” says Gonzalez.

The idea is a boon for the biodiesel industry, which after several years of phenomenal growth, suffered reduced production for the first time last year. Along with the global funding squeeze, increased prices of soy and corn, commonly used as starting products for biodiesel, took their toll. The industry saw a 15 percent drop in total biodiesel production—more than 350 million fewer liters than 2008’s record high of 2.5 billion.

Biodiesel producers hope to boost profits by generating revenue from their primary waste product. “Our producers don’t think of it as waste, it’s a co-product of production, and can potentially have its own market value,” says Jessica Robinson of the Jefferson City, Mo.-based National Biodiesel Board, an industry group consisting of biodiesel companies and research groups.

New Energy Sources

Gonzalez first made news headlines in 2007 by using unmodified E. coli to ferment glycerol into ethanol. E. coli prefer oxygen-rich environments, and normally perform poorly during anaerobic fermentation reactions.1 But after modifying the growth media and pH, Gonzalez was able to coax wild-type E. coli to ferment crude glycerol, yielding about 4 liters of ethanol from every 6 kilograms of crude glycerol—enough to stretch 34 liters (9 gallons) of gasoline into almost 38 (10 gallons). “If you make E. coli really happy, they can handle the stress of not having oxygen,” says Gonzalez.

These results led Gonzalez to found GlycosBio in 2007, a Houston, Texas-based startup that plans to sell ethanol and other products made from crude glycerol fermentation. This winter, the company repeated Gonzalez’s early bench experiments in much larger quantities (250-liter vats), and obtained similar results, suggesting that the process is feasible at the industrial scale. With this success, GlycosBio plans to open its first full-scale plant in Malaysia in 2012. The company’s strategy is to build within blocks of several biodiesel producers, so they can buy their waste glycerol.

The ethanol produced from the reaction can be sold as fuel, or as an industrial-grade chemical to pharmaceutical companies. Alternatively, ethanol can even be added directly to biodiesel and sold as a mixed fuel. Biodiesel manufacturers may eventually license the technology to make ethanol in-house, turning their own crude glycerol waste into a cash product.

Crude glycerol fermentation can also offer additional sources of energy—and money. Along with making ethanol and other fuel additives to sell, the reaction generates electricity and hydrogen power, which can help run a plant’s operations and reduce utility bills.

By harnessing extremophile bacteria to break down crude glycerol, University of Minnesota professor Jeff Gralnick also makes electricity. First found in the oxygen-deprived depths of Oneida Lake in upstate New York, Shewanella oneidensis have an interesting tactic for dealing with the waste electrons produced while breaking down food. While most other organisms make acid and water out of the electrons, S. oneidensis traffics them directly out of the cell through specialized cell membranes.2

By growing the bacteria on graphite slabs that receive the electrons dumped by the bacteria and conduct the resulting current,3 Gralnick can produce electricity in addition to ethanol. “They aren’t designed to eat glycerol, but once you get them on this path, they do amazing things,” says Gralnick, who gets donations of crude glycerol from a local tow truck company that makes its own biodiesel.

The power generated from the fermentation reaction can be stored in a battery, or perhaps used to run small devices. Gralnick says it’s too early to predict the bacteria’s potential, but he is hopeful the electricity will offset processing costs. “It’s not going to be enough to power a building, but we will probably get some use out of it,” he says.

Gonzalez’s E. coli may also serve as an additional source of bioenergy when utilized to ferment crude glycerol. But instead of generating electrical current, his E. coli make hydrogen power. When the bacteria ferment glycerol into ethanol, waste molecules such as formic acid are made. As the bacteria begin to break these apart, hydrogen gas and carbon dioxide are released.

Hydrogen can be harvested directly from the vats in which E. coli are grown, and used in hydrogen fuel cells, which convert hydrogen and oxygen into water, making electricity in the process. Alternatively, the escaping hydrogen can be burned to make energy.

“Once up and running, a good portion of the power for our plant will come from hydrogen—a coproduct of the reaction,” says Paul Campbell, chief scientific officer at GlycosBio. “It’s too early to know for sure, but we will probably make between 50 and 90 percent of our power this way.” This could save the company as much as $3 million each year, he says.

Methane digesters—enclosed lagoons or tanks that hold decomposing material—offer yet another way to harvest energy from waste glycerol, says microbiologist Mike Cohen of Sonoma State University in Santa Rosa, Calif. In most digesters, cow manure or wine waste is broken down by naturally occurring bacteria, releasing methane that can fuel electricity generators. Adding crude glycerol to the mix appears to yield more methane for the same volume of these products, or it can serve as a primary substrate for the reaction. “One gallon of waste glycerol per day could provide enough methane to serve the natural gas demand of one Sonoma County resident,” says Cohen, who is testing the efficiency of the different substrates.

Waste or Product?

Alongside ethanol and butanol, contaminants are produced during fermentation reactions, which can decrease yields. Sometimes, however, these so-called “contaminants” can be sold on the market as separate products, adding extra value to each batch of crude glycerol produced.4

At the University of Alabama in Huntsville, chemical engineer Katherine Taconi is using Clostridium pasteurianum bacteria to convert glycerol to butanol, and grappling with a by-product called 1-3 propanediol—a solvent used to make paint and antifreeze.5 The chemical is produced during the bacteria’s fermentation reaction, and if genetic engineering experiments go well, Taconi’s technology could be used to mass-produce either substance. “1-3 propanediol and butanol are made by competing pathways,” says Taconi. “By reducing one, you get more of the other.”

1-3 propanediol could be sold as an industrial chemical, but it would face steep competition from existing manufacturers. Thus, butanol is Taconi’s current product of choice. “[Our technology] can’t compete as well in the 1-3 propanediol market, so our end goal is to clean up the reaction so we get more butanol,” she says.

In other cases, researchers say the “contaminants” produced during glycerol fermentation may be even more valuable than the main products. When making ethanol, for example, Gonzalez’s E. coli also produce small amounts of lactic acid, which is used to flavor foods, or help prepare fabrics to receive dyes.6 Gonzalez recently found a way to harness a well-known metabolic pathway to increase lactic acid yields. “This is a pathway we knew played a role in glycerol metabolism, but no one knew it could be harnessed to produce lactic acid,” he says.

Two other contaminants, succinic acid and propylene glycol, can also be put to use by the pharmaceutical and cosmetic industries, Gonzalez says. “On a pound-for-pound basis, you can actually make more of these substances than ethanol, so you get more of a sellable product from the same amount of glycerol.”

While there is no shortage of useful options for crude glycerol—after it’s refined, it can even be used in cattle feed, or sold for use in hand sanitizers and cosmetics—the truth is most biodiesel producers currently pay to dispose of the gunk, or give it away for free because they have so much of it. The charm of ethanol fermentation is that it creates a new source of revenue for dirty, unrefined glycerol.

“We need to get as much value as possible out of our waste products,” says Taconi. “This means finding uses for crude glycerol, and harnessing the co-products from the fermentation reaction.”

Is biodiesel environmentally friendly?

Burning biodiesel reduces emissions of greenhouse gases and many other air pollutants, and farming corn and soy—common starting products for biodiesel—can help reduce carbon dioxide levels even further. But as the biodiesel industry grows it will likely increase the acreage farmed using industrial methods, which pose their own environmental concerns.

Most often grown as monocultures on large industrial farms, these crops inevitably have pest problems, and farmers often turn to pesticides and herbicides. The crops are treated with some of the most controversial chemicals on the market, and residues are sometimes found in tap water miles away from application sites. Furthermore, genetic modification (GM) campaigns contaminate traditional seed stocks, according to the Union of Concerned Scientists, and often require higher pesticide applications, contrary to conventional thought. Many worry that the industrial agriculture lobby may even try to leverage the environmental benefits of biodiesel to justify weaker regulations for pesticide use and GM standards.

Deforestation is also a concern. Native forests are already being clear-cut in Indonesia to make way for biodiesel farms and palm plantations, another primary source of the fuel. Destroying grasslands and rainforests for biofuel crop can results in up to 420 times more CO2 in the atmosphere than if fossil fuels are used, according to the Nature Conservancy.

Thus, getting the most out of each acre of cropland diverted to fuel may make the industry more sustainable, says Katherine Taconi of the University of Alabama in Huntsville. “Along with selecting for sustainable starting products, we also need to integrate wastes like crude glycerol back into the fuel manufacturing process,” she says.

1. R. Gonzalez et al., “A new model for the anaerobic fermentation of glycerol in enteric bacteria: trunk and auxiliary pathways in Escherichia coli,” Metab Eng 10(5):234–45, 2008.
2. D. Baron et al., “Electrochemical measurement of electron transfer kinetics by Shewanella oneidensis MR-1,” J Biol Chem, 284(42):28865–73, 2009.
3. D. Coursolle et al., “The Mtr Respiratory pathway is essential for reducing flavins and electrodes in Shewanella oneidensis,” J Bacteriol, 192(2):467-74(2010).
4. M. Rodriguez-Moya and R. Gonzalez, “Systems biology approaches for the microbial production of biofuels,” Biofuels, 1(2): 291–310, 2010.
5. K.A. Taconi et al., “Growth and solvent production by Clostridium pasteurianum utilizing biodiesel-derived crude glycerol as the sole carbon source,” Environ Prog Sustain Energy, 28:100–10, 2009.
6. G. Durnin et al., “Understanding and harnessing the microaerobic metabolism of glycerol in Escherichia coli,” Biotechnol Bioeng, 103(1):148–61, 2009.

Correction (posted July 30): When originally posted, the story omitted the full name and affiliation of a quoted source. The story has been updated to introduce Paul Campbell, chief scientific officer at GlycosBio. The Scientist regrets the error.

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