Biotech researchers transform biodiesel waste into additional fuel
Ray Newkirk doesn’t hesitate to wash his hands with dirty soap. Before founding the Green Station on Ocean Street in Santa Cruz, where locals pump Bay-Area-made biodiesel into their cars, Newkirk was a backyard producer, making fuel out of fryer waste from the Saturn Café.
Like other biodiesel producers, Newkirk also inevitably made a lot of dark, thick waste glycerin.
For every 100 gallons of biodiesel made, 10 gallons of the crude goop remain. Last year 600 million gallons of biodiesel were produced, and while a freeze on tax credits has slowed production this year, America will still have millions of gallons of crude glycerol at its fingertips.
The color of molasses and the consistency of oil, the gunk is considered non-toxic, but there isn’t much to do with it.
Many backyard producers, including Newkirk, make soap with their waste. By adding lye, the black glycerol solidifies into a grey block that can be cut into bars of soap. By adding a little less lye, a gel with the consistency of hand sanitizer congeals.
“I used to wash my truck with the stuff, and rub it all over my hands,” says Newkirk. “I have carpenters hands—they are all dry and cracked, and the waste glycerol leaves your hands feeling silky smooth.”
”Silky smooth” may sound straight out of a commercial, but the goop is utterly unattractive—models selling dish soap on daytime TV would never let the stuff touch their manicured hands.
“It isn’t pretty and pink, and it doesn’t have the right fragrance,” admits Newkirk, “and for it to be a really sellable product, you have to refine it.”
Because the refinement process takes time, money and energy, and because the glycerin market is hotly competitive, biodiesel manufacturers say soap made from the waste probably won’t be found on supermarket shelves any time soon.
Even if consumers would buy molasses-colored hand soap, the pure form of glycerol is already manufactured by the cosmetics industry for use in makeup, hand sanitizers and soaps of all varieties. The demand is being met; the market is too saturated for biodiesel manufacturers to jump on board.
So, with a soap market out of the question, what is the biodiesel industry going to do will all of their leftover gunk?
A small handful of metabolic engineers have turned to biotechnology for a solution. They are using common lab bacteria to ferment crude glycerol, leading to the production of ethanol, butanol, and a long list of other useful products made from the waste.
They have found that E.coli—a bacteria grown by many research labs—can be tricked into making lactic acid out of crude glycerin. The acid is used by the textile industry to help fabrics receive dyes. It’s also a component of detergents and sour food products, like pickles.
“We knew E.coli used this pathway when breaking down glycerin, but we didn’t know the genes and enzymes involved could be utilized to make large-scale quantities of lactic acid,” says Gonzalez. He uses genetic engineering to amplify the pathway, and gives the bacteria waste glycerol from a local biodiesel plant. This creates a lot of lactic acid.
Without modification, the bacteria turn crude glycerol into ethanol. For every pound of crude glycerol, the bacteria makes about a half-pound of the biofuel. “This pathway competes with lactic acid production, so if you increase one you get less of the other,” says Gonzalez. While E.coli still produce ethanol without genetic engineering, yields are higher when lactic acid production is minimized.
Gonzalez recently started a company based on these findings. Called GlycosBio, the Huston, Texas-based start-up plans to set up shop near existing biodiesel refineries so that the waste glycerin won’t have to travel far.
Ethanol is most commonly used as a fuel additive—stretching each gallon of gasoline or biodiesel that much farther. Brazil’s flexible-fuel vehicles run on 85 percent ethanol and 15 percent gasoline. Some cars on the U.S. market can run on a 50-50 mixture. Ethanol can also be added to biodiesel, or sold as a stand-alone product for use in the pharmaceutical industry.
While making ethanol from biodiesel waste is important, the findings intrigue scientists for another reason as well. Gonzalez gets E.coli, which normally like to grow in oxygen-rich environments, to do something exceptional. He uses the bacteria to ferment glycerin—much like yeast ferment grain to make liquor. Fermentation reactions happen in oxygen-deprived environments, so the bacteria don’t have any air to breath.
“We were the first to show you could get unmodified E.coli to ferment crude glycerol into ethanol,” says Gonzalez. “Getting them to work without oxygen doesn’t take any genetic engineering, but you have to make [the E.coli] really comfortable. If you give them the right nutrients, they will do good work even though the conditions aren’t ideal.”
By fermenting crude glycerol, researchers can also made propylene glycol, which can be used in cosmetics. Succinic acid is another product—it can be used in biodegradable plastics and pharmaceuticals.
The Green Side of Black
Katherine Taconi, a chemistry professor at the University of Alabama in Huntsville uses a similar process, although her bacteria enjoy working in oxygen-starved environments. By modifying Clostridium pasteurianum she converts waste glycerin from biodiesel plants into a chemical called butanol. Like ethanol, butanol can be added to fossil fuels to stretch each gallon farther.
Yet, like the bacteria Gonzalez uses, Taconi’s creatures make other products alongside butanol—ultimately diluting the final yield. “We are trying to understand the metabolic processes involved so we can engineer bacteria that produce fewer [contaminants],” says Taconi. “We will probably never get rid of them completely, but we can increase the amount of butanol we get in the end.”
University of Minnesota professor Jeff Gralnick is harnessing a different kind of bacteria. Discovered at the depths of New York’s Lake Oneida 20 years ago, Shewanella oneidensis are being engineered to break down glycerin into ethanol.
The bacteria have another quirk—they produce electricity, and this can be harvested along with the ethanol produced. S. oneidensis naturally release electrons through proteins in their cell membranes. Usually these electrons are dumped onto iron and manganese oxide rocks, where the bacteria like to grow. When the underwater rocks receive the electrons, their chemical structure changes and they become soluble. The bacteria are thus infamous for their ability to dissolve rocks—albeit, very slowly.
Gralnick is growing the bacteria on graphite slabs, which don’t dissolve. These also conduct the electrons in the form of electricity. “There are too many electrons per molecule of glycerol, so when you break it down to make ethanol, there are a bunch of free electrons that have to go somewhere,” says Gralnick. Called a microbial fuel cell, his technology harnesses this flow of electrons to make electricity.
As crude glycerin can even be composted under the right conditions, there is no shortage of disposal solutions. The trick—and desire—is to make money doing it. “It’s a valuable product,” says Taconi, “so the question is what to do with it at the industrial scale. How can we make the most of it?”
Newkirk says these solutions might help lower the price of biodiesel over the long term. If producers can sell their waste products to another company, and support a value-driven industry, they can pass profits onto consumers.
“In general I think it’s a great idea,” he says, adding that making crude glycerol also gets more fuel out of each acre of cropland. “Any way we can get ourselves off petroleum is a good thing. But biodiesel needs to be affordable, or people won’t buy it.”
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