About 10,000 years ago, humans learned how to put yeast to work to brew beer.
Now, as the scientific community struggles to develop a way to produce hydrogen for fuel cells, some researchers are including microorganisms in their recipes for making electricity.
With a reliable source of hydrogen, fuel cells can produce energy with water as the only byproduct.
Here's the problem: While hydrogen is the most abundant element in the universe, it is extremely difficult to capture and store in its pure form. Just as potable water cannot be found in the middle of the ocean, usable hydrogen remains scarce in the sea of organic compounds surrounding us.
The methods of manufacturing and compressing hydrogen gas require great amounts of energy. To overcome these challenges, scientists have been tinkering with the biological powers of everything from common yeast to mysterious bacteria living on the ocean floor.
At the University of California at Berkeley, mechanical engineering professor Liwei Lin is busy developing a microbial fuel cell that runs off the digestive activity of baker's yeast. The yeast feed on glucose, a simple sugar, and digest it in a process called aerobic metabolism.
"We extract electrons from the yeast cells where the aerobic metabolism process happens," Lin explains.
Controlling the movement of electrons to harness a renewable source of fuel remains the target for scientists designing fuel cells, which extract power from electrochemical reactions. The advantage of Lin's mechanism is that it runs on glucose, a naturally abundant resource produced by plants.
One of his small prototypes, measuring 0.7 square centimeters and less than 1 millimeter thick, produces 1 microwatt of power -- approximately enough to power a digital wristwatch.
Lin believes it is only a matter of time before fuel cells in laptop computers will recharge from glucose cartridges. He plans to adapt his prototype to use glucose found in the bloodstream to power implantable devices such as internal pacemakers.
With the help of a $300,000 grant from the National bet365体育赛事 Foundation, Lin's lab will expand its work on other types of microbial fuel cells. They hope to refine a new system that extracts power from the photosynthetic activity of algae.
"The prototype we have tested has very poor efficiency -- less than 1 percent," Lin said. "We believe that we can engineer this technology much better to have higher efficiency than gasoline-based combustion engines."
Suellen VanOoteghem, a researcher at the National Energy Technology Laboratory in Morgantown, West Virginia, also believes in the potential of microorganisms to revolutionize our power grid. She and her team study heat-loving bacteria that eat glucose, then pass gas in the process of breaking down their food. But the gas these microorganisms release is more useful than it is offensive.
Under optimal conditions, a 14-liter reactor in her lab produces waste gases that are up to 80 percent hydrogen. VanOoteghem estimates that the activity of bacteria in a 53-cubic-foot reaction chamber would provide enough hydrogen to run a 200-kilowatt fuel cell and supply energy for about 20 houses.
The exact enzymatic pathway by which these bacteria (known scientifically as T. neapolitana) produce hydrogen remains unknown, although researchers are working to map the microorganism's genome.
Another approach to microbial fuel cells takes the technology to new depths. Leonard Tender, who leads a team at the U.S. Naval Research Laboratory in Washington, D.C., and Oregon State University professor Clare Reimers have co-invented a device that draws on the electron-rich environment created by microorganisms in ocean sediment.
Over millennia, microbes in undisturbed ocean mud digest dead organisms such as phytoplankton and then unload electrons onto surrounding chemicals. The fuel cell designed by Tender and Reimers employs two connected graphite disk electrodes (one placed in the sea-bottom muck and another in the water above) to generate a current by carrying these electrons up and away from the sediment.
One small prototype of the device produces 10 milliwatts of energy. When scaled up to about 1 watt, it has the potential to power a variety of oceanographic instruments that monitor such things as temperature and chemical substances in the water. Ideally, it would recharge the batteries in these instruments and power them indefinitely.
"The major obstacle is that the fuels in the sediment and the bacteria there are present in a diffuse way," Reimers said. "There's a wide resource ... but it's widely dispersed. The challenge is to tap into that."
Both Reimers and Tender have tested prototypes in shallow waters. They plan to explore more concentrated sources of fuel coming from bacteria that live near geochemical seeps at greater ocean depths. The trial will involve deploying a test fuel cell at a 1,000-meter-deep site at the bottom of Monterey Bay off the coast of central California.
Tender imagines that methods of extracting energy from the ocean floor have great potential. "Who knows? Maybe one day we can power a city," he said.
Gregory Zeikus, a professor of biochemistry and microbiology at Michigan State University, agrees that microorganisms could power the future. He conducts experiments to find the best chemicals and enzymes to extract energy from sewage.
"There are enough electrons in the waste that goes through a city's treatment plant in a day to power a city," he said.
Zeikus already has tested his fuel cells on sewage sludge from the wastewater treatment plant in Lansing, Michigan. Instead of allowing the microbes in the waste to produce methane, he prods them to make electricity by adding an "electron mediator" -- a substance that allows him to tap into their cellular circuitry.
Zeikus explains that scientists have been interested in microbial fuel cells for two decades. Until recently, though, a lack of good electron mediators prevented major advances. One of the best mediators he has found, known as neutral red, is a common dye once used in food coloring.
"In order to make the electricity cost-effective, we have to improve the rate of electron flow by 10,000-fold," Zeikus said. "We also only extract about 30 percent of the total energy that you can degrade from sewage waste.
"We want to make that three times better and leave 10 percent for the bugs," Zeikus said.
