Hydrogen from microscopic algae fuels cars
If hydrogen is the fuel of the future, Tasios Melis says he thinks he has struck oil. His research team has discovered how to turn on a microscopic algae's ability to photosynthesize hydrogen big time. If they now can boost that hydrogen production tenfold, as calculations predict they can, Dr. Melis says they will have a commercial-scale experiment running.
Scientists have studied algae hydrogen production for many years. However, the tendency of the process to shut itself down has frustrated their efforts. That's why Melis calls his new ability to turn the process on and keep it running a major "breakthrough."
To emphasize its long-range promise, he estimates that a commercial operation based on this discovery could supply the fuel for about a dozen cars from a small pond full of green scum and water. But right now, the importance of the work pursued by Melis's University of California team in Berkeley and by partners at the National Renewable Energy Laboratory in Golden, Colo., is that it opens up another line of research that could lead to a future hydrogen fuel economy.
Margaret Mann at the Golden laboratory explains that hydrogen could solve "a lot of the global climate change problem we have with fossil fuels [as well as] the air pollution." Fuel cells that "burn" hydrogen and oxygen to make electricity produce only water as their waste product. Generating the hydrogen from sunlight and water would put that energy economy on a renewable basis.
When Melis described his breakthrough during a meeting of the American Association for the Advancement of Science last month in Washington, D.C. Dr. Mann noted that scientists know how to produce hydrogen with the help of solar cells. The cells generate electricity that, in turn, splits water into hydrogen and oxygen. Now, she says, scientists have "a new technology" to explore.
Meanwhile, the search is on for other organisms that can photosynthesize this useful gas. For example, Tadashi Matsunaga from the Tokyo University of Agriculture and Technology in Japan told the Washington meeting that his group is finding marine microorganisms that can produce various useful products. They include plant-growth regulators and antimicrobial compounds, as well as hydrogen.
Right now, the work of Melis and his colleagues has produced the most spectacular results. They use a microscopic green algae with the formidable name Chlamydomonas reinhardtii. It normally uses sunlight to make carbohydrates from carbon dioxide and water like other green plants. Oxygen is a byproduct. However, the algae needs a sulfur-containing compound in its growth medium. Withdraw the sulfur and photosynthesis stops.
Plants use oxygen to burn fuel they have stored to carry on life processes. Generally, if a green plant can't produce its own oxygen photosynthetically, and is in an oxygen-poor environment it suffocates. Melis's algae just switches to what he calls "an alternative form of breathing." This enables it to live on its stored compounds through a process that releases hydrogen.
Researchers who tried to switch on this process in the past were frustrated because any residual oxygen immediately shut it down. Melis and colleagues tried a new technique. They transferred their algae slurry to a bottle where there was absolutely no sulfur present. Photosynthesis stopped. After about 24 hours, the algae used up any residual oxygen and switched on their hydrogen-producing mode. They continued producing hydrogen for about 4 days until they used up their stored carbohydrates and other fuel compounds. A liter of algae slurry produced about 0.3 liters of hydrogen in that period.
This is a renewable process. Algae in a bottle with a growth medium that supplies sulfur makes carbohydrates photosynthetically. Transfer the algae to a sulfur-free bottle and, after a short time, it uses those carbohydrates to make hydrogen. When that fuel is depleted, transfer the algae back to a bottle with a sulfur supply and normal photosynthesis builds up more carbohydrate and other "fuel" compounds. Melis's colleague Maria Ghirardi at the National Renewable energy Laboratory says that "the cell culture can go back and forth like this many times."
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