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Where does the Carbon go?

DoE News: Berkeley/NREL Team Develops Green-Algae-Based Renewable H2 Production Technique 

BERKELEY, CA/GOLDEN, CO - It sounds a little wild, but a lowly micro-organism, a green alga, may come one of the milk cows of the hydrogen age. Better make that "fuel" cows. 

Voila, the hydrogen herd: 

Cultures of tiny algae, Chlamydomonas reinhardtii, can be conditioned via a simple microbial switch to forego what they normally do best: produce plant matter via photosynthesis  and give off oxygen in the process. Instead, switched-on algae would produce hydrogen renewably, essentially from sunlight and water,  stored in its cells as carbohydrates and other biochemical materials. 

Nor is this process, discovered by a team of researchers at the University of California, Berkeley, and at the National Renewable Energy Laboratory (NREL) in Golden, CO, a one-shot proposition that would kill the "cows:" After generating hydrogen for several days, the gas can be drawn off and  the molecular switch can be reversed again, permitting the algae to recover to their normal state and  produce more plant matter, including carbohydrate fuel. 

That process can be repeated "many times," says Prof. Tasios Melis, a specialist in plant and microbial biology at Berkeley who heads the team. How many times isn't clear so far. 

At present, the overall energy conversion efficiency of the process - photons absorbed and converted into hydrogen product - is only about 10%. But, says Melis, with optimization, it could come close to or be about the same as photosynthesis itself: With the right amount of light - not too much because otherwise photons would be wasted - it could be anywhere between 85 and 90%, possibly as high as 95%. "Photosynthesis is nearly perfect machinery," Melis says. 

The work has already attracted wide public attention. A  press briefing in late February in Washington, DC, arranged by the American Association for the Advancement of Science and scheduled for one hour, lasted a lot longer because the 45-odd reporters kept asking questions past the cut-off time. Stories by the Associated Press, Reuters and BBC generated later phone calls from as far away as Portugal and Greece, Melis said. 
Two-Year Investigation 

Melis, together with postdoctoral associate Liping Zhang and with NREL's  Michael Seibert,  Maria Ghirardi and postdoctoral associate Marc Forestier, described the outcome of their two-year investigation, the result of a suggestion made at an April  1998 hydrogen workshop sponsored by the Energy Department and the National Science Foundation, in a paper in the January 2000 issue of the journal "Plant Physiology."  Both institutions have taken out a joint patent for the process. 

"I guess it's the equivalent of striking oil," a university press release quoted Melis as saying. "It's enormously exciting." 

The fact that green algae can produce hydrogen has been known for more than half a century, the team reported, but only in very small amounts. 
 The production rates of the new Berkeley/NREL process  are very small so far as well, but Melis thinks this novel process can be sufficiently improved to make it an economically viable source of hydrogen gas. The release quoted him as believing that  a small commercial pond stocked with the algae could make enough gas to meet the weekly fuel needs of a dozen or so cars. 

The "Plant Physiology" article describes the Berkeley/NREL process as a single-organism, two-stage process which  separates, over  time,  the normally simultaneous processes of oxygen evolution and carbon accumulation  - I.e.. the production of plant matter  - from the consumption of metabolic cell material, accompanied by the production of hydrogen gas. Normally, hydrogen evolution is  suppressed in a natural fail-safe system in a plant (simultaneous production of oxygen and hydrogen gas is not of benefit to the cell; in fact  it would produce a potentially explosive gas mixture). Oxygen itself acts as an effective molecular switch, turning off the hydrogen production reactions). 

Starving Cells of Sulfur is Key 

The key discovery was that depriving the algae of inorganic sulfur reversibly inactivated the functioning of what's known as photosystem II, which includes the generation of oxygen. Without sulfur, the metabolic pathways change, enabling the algae to function without generating oxygen. After about 24 hours of sulfur deprivation, the plant becomes anaerobic, activating an enzyme that produces hydrogen in the light. 

Without sulfur, "they're utilizing stored compounds and bleeding hydrogen just to survive," said Melis. "It's probably an alternative form of breathing, an ancient strategy that the organism developed to live in sulfur-poor anaerobic conditions." 

 Normally, algae cells use light's energy to perform photosynthesis which makes sugar, oxygen and the high-energy molecule ATP (adenosine triphospate) from carbon dioxide and water. ATP in turn is a key ingredient in the plant's ability to carry  out vital functions, including cellular maintenance, repairs and essential biosynthetic processes in the absence of normal photosynthesis due to the lack of sulfur and absence of respiration due to the lack of oxygen. 

Under those conditions, every other organism would normally suffocate, explains Melis. These green algae, however, have a trick: they activate the alternative pathways that permit them to generate ATP, giving off hydrogen as the end product of the alternative process. Melis and his colleagues have demonstrated that the hydrogen-producing enzyme stays active for days, producing hydrogen in the light in a sustainable 
A Simple Process 

The process is essentially simple, says Melis: "We provide the algae with enough sulfur to perform photosynthesis and accumulate sugars, proteins, lipids and cellular matter. Then we deprive them of sulfur. This forces the cell to burn and utilize the fuels they have accumulated, producing hydrogen as a byproduct." 

Keeping algae on a no-sulfur, no-oxygen  diet stresses the cells, and they cannot survive indefinitely. But sulfur can be  added again after enough hydrogen has been collected. The  cells  recover, relaunch normal photosynthesis and replenish cellular matter once again. Once the cells have been "fattened up," the process cycle can be repeated. 

Earlier  experiments attempted to switch off photosynthesis and produce hydrogen by keeping the algae in dark rooms. It worked, of sorts, but the yield was too small to make it viable, producing only microliters of hydrogen gas. 

The new Berkeley/NREL approach works in the light, and in early tests produced 2-3/10th of a quart - an improvement over the dark process by several orders of magnitude.  A table in the  journal paper said the team 
generated 140 milliliters of hydrogen in 80 hours. Protein and starch contents of the substrate solution, a lime green liquid, in the one liter bottle were reduced by 52 and 25%, respectively. 

The experiments showed "for the first time, to our knowledge, that it is possible to produce and accumulate significant volumes of H2 gas using C. reinhardtii in a sustainable photo biological process that can be employed continuously for several days," the authors summarized their findings. Significantly, "the process depends on physiological treatment of the algae culture, not on the mechanical or chemical manipulation of the cells," and with more research and development, it "could generate renewable H2 for the fuel and chemical industries."  
Contact: Tasios Melis, e-mail melis@nature.berkeley.edu; fax 510/642-4995. 










It Came From the Swamp

Reengineering Algae To Fuel The Hydrogen Economy.

The coming hydrogen age promises guilt-free SUVs and factories that belch steam instead of smog. But where will all that hydrogen come from? California startup Melis Energy thinks it has the answer: genetically enhanced pond scum.

Traditional methods of extracting hydrogen from H2O take electricity, which usually means torching fossil fuels. Alternatives exist, but solar cells are pricey, and windmills are limited to windy areas. Industrial hydrogen producers get their supply by blasting natural gas (CH4) with scalding steam, and fuel cells use a similar method to strip hydrogen from gasoline, wood alcohol, or methane. In other words, hydrogen production may be a big improvement over internal combustion, but it still unleashes plenty of greenhouse gases. So what to do?

Use algae, says Tasios Melis. His breakthrough came in 1998 when, as a UC Berkeley biochemist, he was tinkering with green algae, trying to coax the plants to convert water into hydrogen. Algae have long been known to produce minuscule amounts of the gas. Trouble is, the enzyme that propels the reaction (hydrogenase) stalls in the presence of oxygen, and - think back to high school bio - plants naturally produce oxygen during photosynthesis.

Melis found he could reprogram photosynthesis and stifle internal oxygen flow by depriving the plant cells of sulfur. Under these conditions, the algae pumped out hydrogen for days at a time - lots of it. "We thought maybe we'd get a little hydrogen," Melis says. "But it came out in bulk amounts." An acre of his pond scum, he calculates, could produce enough H2 to power a car from Sacramento to Seattle - and theoretically much farther.

Recognizing the commercial possibilities, Melis and his colleagues applied for a patent and published their results in 2000. Last year, he recruited entrepreneur Steve Kurtzer as CEO and engineer James Candy as director of engineering, and Melis Energy was born. The startup's goal: license the technology to power generators, fuel wholesalers, and hydrogen producers. Kurtzer is negotiating with private investors for $10 million to cover R&D. If that comes through, Melis and Kurtzer predict their algae will hit the market in two to five years.

Melis sees widespread applications for his method. "This is low tech," he says. "It won't require fancy equipment or industrial facilities. A farmer could do it." The company is trying to patent a tubular bioreactor - a network of sealed tubes - for cultivating algae and extracting pure hydrogen. Each unit might hold 5,000 to 10,000 gallons. A megaplant could hold as many as 1 million.

At the moment, Melis' method won't cut it in the marketplace. The algae-hydrogen system generates electricity that costs about 31 cents a kilowatt-hour. Natural gas-fired juice runs a nickel or less. But a solution is in sight. Melis' team recently uncovered the key bottleneck in its green biomachine: Hydrogenase is present in only tiny amounts. By genetically engineering algae that express high levels of the enzyme, the team expects to double hydrogen output.

Still, if you thought solar power was fringe, try selling algae to the big boys. Algal fuel is certain to face skepticism and stiff competition. Natural gas isn't going anywhere, and cost-saving advances in solar, wind, and biomass conversion are inevitable. "What Melis has done is the most advanced to date in the biological area," says Seth Dunn, an energy expert at the Worldwatch Institute. "I'd put it in the wild card category." Then again, that's what they said about the horseless carriage.

- Michael Mechanic


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