Biologically Derived Hydrogen--Future Fuel?

Courtesy of Carla Santee A NEW KIND OF BUBBLY: Suellen Van Ooteghem's bioreactor is producing a gas that is 80% hydrogen: "These results are unprecedented." A large glass bioreactor in the corner of Suellen Van Ooteghem's lab at the National Energy Technology Laboratory is filled with what appears to be murky champagne. The pale yellow solution even has tiny bubbles streaming to the top. The liquid is arguably as precious as any champagne, and the bubbles are even more valuable: They are almost pure hydrogen. Hydrogen, it's been said, is the fuel of the future. When used in fuel cells to create electricity, the only pollutant is water. But what prevents hydrogen from replacing oil as this country's main source of energy are a bundle of engineering hurdles. The greatest technological obstacle is the high cost of producing hydrogen cheaply and cleanly. The most promising current technology is the use of nuclear energy to heat water and blast natural gas with steam, stripping off the hydrogen ions--not exactly clean and green. For decades, researchers had been looking for just the right organisms to produce massive amounts of hydrogen. Those years of investigations culminated in a handful of microbes identified as capable of doing so. A few dozen life scientists are racing to fine-tune these microbes physiologically, chemically, and genetically to produce hydrogen in a cost-effective manner with next-to-zero pollutants. The reward is enormous. Not only could it prevent further global warming, slash energy pollution, and strengthen the economy, but the winner of this race would own the intellectual property rights to the technology that could be at the foundation of a multitrillion dollar industry. In other words, the gold rush is on. FROM DUNG TO DOLLARS Van Ooteghem's bioreactor is located at the energy technology's lab in Morgantown, W. Va. She isn't exactly sure what's going on inside the Thermotoga neapolitana bacteria that live in the bioreactor. What she does know is that the 14-liter vessel is producing about eight liters of waste gas every hour, as much as 80% of which is hydrogen. "These results are unprecedented," she says. Her tiny five-person lab has subsisted on about $150,000 (US) a year in research funds. "When we started this work seven years ago, we wished we could reach 30% [hydrogen]." Her first paper on this research published in 20021 claimed 30% hydrogen production, and even that amount created a ripple of excitement in the field. The mystery is that T. neapolitana, a class of microaerophilic extremophiles that operate at peak efficiency at around 75°C, do not appear to be using the known enzymatic pathways for hydrogen production. Most bacteria that produce hydrogen harvest it from sugar under anaerobic conditions, otherwise known as fermentation. Van Ooteghem's bugs do use sugar for their housekeeping tasks, but they appear to be producing hydrogen from ammonium. And, most surprisingly, they're doing it in the presence of oxygen. In other words, this is not a fermentation process, which was previously thought to be the only way that bacteria could make hydrogen. The implications of Van Ooteghem's research are remarkable. Crystallized urea--her ammonium source--is a very cheap byproduct of wastewater treatment plants. "The concept that the bacteria are using the ammonium as a hydrogen source makes sense. Ammonium [NH4] is packed with hydrogen," says Randy Wayne, a Cornell University biologist. "I don't know of any bacteria that do that, but there are billions of biological processes that bacteria do that haven't yet been discovered." Others doubted Van Ooteghem's results. Karen Nelson, a geneticist at the Institute of Genomic Research, traveled to Morgantown, observed the instruments, and took genetic samples. She confirmed that the bacteria were indeed doing what Van Ooteghem claimed. "I heard about her results and was suspicious," says Nelson, "but everything checked out. She has really discovered something amazing." Nelson recently received a Department of Energy (DOE) grant to sequence the genome of T. neapolitana, a task that will require as long as a year. Courtesy of The Institute for Genomic Research TIGR DOUBTER: TIGR's Karen Nelson was a skeptic; now she's going to sequence the T. neapolitana genome. Van Ooteghem's biggest immediate challenge is simply to publish her results. "We keep getting more and more fascinating information, [so] ... we put off the papers," she says. "Right now I'm too excited to stop and work on writing." Her team is in the process of writing three papers explaining the results. Without publication, it's hard for other scientists to recreate her work. One lab in the Netherlands failed to produce the same amounts of hydrogen, but did so under conditions very different from Van Ooteghem's. "We used a batch sample, not a continuously running reactor," says Heleen Goorissen, a Wageningen University researcher who conducted the studies. If Van Ooteghem's results hold up to scrutiny after publication, her system should be able to scale up to industrial proportions. For one thing, the high temperature of the bioreactor kills other microbes, which means sterile conditions aren't necessary--a big money saver. Also, she can stop the hydrogen production quickly, simply by lowering the temperature in the reactor. ALGAE DEPRIVATION Bacteria aren't the only candidates for the biological production of hydrogen. In 2000, Tasios Melis of the University of California at Berkeley made headlines by tricking Chlamydomonas reinhardtii, the common green algae, into producing hydrogen instead of carbon dioxide during photosynthesis.2 His secret was to deprive the algae of sulfur, and the algae responded by producing hydrogen. Unlike the process used by Van Ooteghem's bacteria, the algae simply strip the hydrogen atoms from water in a process very similar to electrolysis, producing very few waste gases other than nitrogen. Here, however, the biggest obstacle to squeezing the most hydrogen out of the algae is the large size of the cell's photoreceptors. "There's too much chlorophyll in the cell, so nearly 60% of the photons that are captured are burned as waste heat," says Melis. "Essentially, we're trying to alter the optical properties of the algae so that all of the energy is used to mine hydrogen from the water." He's doing that by tinkering with the algae chemically, physiologically, and genetically. Right now, Melis can coax the algae to produce 10% of their maximum yield of hydrogen. According to his calculations, that means he can produce enough hydrogen to produce electricity at $.70 per kilowatt. If he ever reaches the 100% point--which he's convinced is attainable--he can bring that cost down to $.07 per kilowatt. That's only $.02 more per kilowatt than the cost of using natural gas. Further improvements to reactor design and recycling of the feedstock of inorganic chemicals could halve that cost again. "The roadmap to cost-effectiveness is visible; it's just a long road ahead," he says. BEST OF BOTH WORLDS Another research group hopes to combine the "dark" fermentation process with the "light" method of photosynthetic bacteria. The large European project includes 45 members spread throughout Europe and is led by Pieternal Claassen of the Agrotechnological Research Institute in Wageningen, Netherlands. They've applied to the European Union's Sixth Framework Programme for a ¤20 million, five-year grant to build a pilot industrial plant. According to their plans, they will ferment agricultural waste in a large anaerobic reactor, relying primarily on an extremophilic bacterium, Caldicellulosiruptor saccharolyticus. That process releases some hydrogen and also creates acetate. Then the brew is transferred to a glass-encased reactor filled with the photosynthetic bacterium from the Rhodopseudomonas species. That microbe specializes in breaking down acetate into hydrogen and carbon dioxide. The waste stream can then be burned to produce more energy. If all goes according to plan, they hope to harvest as much as 60% of the hydrogen from the feedstock. Probably the most audacious research in this area is the work at the Institute for Biological Energy Alternatives, Rockville, Md., led by none other than J. Craig Venter. He recently received a $3 million DOE grant to create a new organism: an extremophile bacterium whose genome is stripped of all but those genes needed for basic life. Once they have done that, Venter and collaborator Hamilton Smith hope to add genes for hydrogen production. They want to create, from scratch, the ideal hydrogen-producing vehicle. Most scientists in the field feel awe at the scope of Venter's ambitions, but aren't sure it's going to work. "He's trying to create a nucleus and drop it into a polysaccharide sac; in other words, he's building a living thing," says Bruce Nelson of Pennsylvania State University's Hydrogen Energy Center. "It's admirable and amazing, but I fear the hydrogen production aspect is just an add-on to justify the grant money." Van Ooteghem also doubts Venter's approach, even though she says that Venter should be successful. "He's working from the ground up when nature already provides us with a nearly finished work," she says. "Hydrogen-producing organisms exist throughout nature. They don't need to be rebuilt. They just need a little tinkering." Sam Jaffe (sjaffe@the-scientist.com) is a freelance writer in Philadelphia, Pa. References 1. S. Van Ooteghem et al., "Hydrogen production by the thermophilic bacterium Thermotoga neapolitana," Appl Biochem Biotechnol, 98-100:177-89, 2002. 2. A. Melis et al., "Hydrogen production. Green algae as a source of energy," Plant Physiol, 127:740-8, 2001.

Biologically Derived Hydrogen--Future Fuel?

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