NEWPORT, Ore. - During the past two years, scientists have successfully tapped the chemical reactions from decomposing organic matter on the ocean floor to create fuel cells that can provide low levels of electrical power for many months.
This week, Oregon State University researchers announced that they have taken that development one step farther by harnessing the same power-producing decomposition activity from plankton taken from the upper water column.
"We've only had the experiments running for about four weeks," said Clare E. Reimers, a professor in the College of Oceanographic and Atmospheric Sciences at OSU, "but it is clear that we can use plankton as a fuel source and that the water column is rich in microorganisms adept at shuttling electrons to fuel cell electrodes. The seafloor fuel cells that we've developed in the past are stationary and designed to provide power for equipment that doesn't move - like the hydrophones used by the U.S. Navy or by OSU researchers for listening for earthquakes.
"But by harnessing plankton power, we potentially could fuel autonomous, mobile instruments that would glide through the water scooping up plankton like a basking shark, and converting that to electricity," she added. "Such instruments carry sensors and are used today to map the changing chemical and physical properties of the ocean."
Reimers is director of the Cooperative Institute for Marine Resources Studies, a program designed to foster collaborative research between OSU and the National Oceanic and Atmospheric Administration (NOAA). In 2001, she was the lead author of a publication in the journal Environmental Science and Technology that outlined some of the pioneering work that has led to the harnessing of microbially generated power from the seafloor and further publications.
In three seafloor experiments to date, researchers from OSU, the Naval Research Laboratory, the University of Massachusetts-Amherst, and the Monterey Bay Aquarium Research Institute have tested prototype fuel cells in Newport's Yaquina Bay, in a salt marsh in Tuckerton, N.J., and at chemical seeps in a deep-sea canyon off Monterey, Calif. These devices consisted of graphite anodes shallowly imbedded in marine sediments connected to graphite cathodes in the overlying seawater.
They found that power was generated both by the direct oxidation of dissolved sulfide - which is a byproduct of microbial decomposition - and by the respiration processes of microorganisms that attached themselves to the anode.
"Once we realized we could harness power from the microbes that grow on the anode surface, we began asking ourselves if certain microbes were better at shuttling electrons than others," Reimers said. "The next step was to see what electricity-loving microbes might be enriched from plankton and if we could get to the energy in plankton before it degrades.
"The plankton detritus that reaches the seafloor is usually only the dregs of material made energy-rich because of sunlight and photosynthesis." In March, Reimers and her colleagues received funding from DARPA, the Defense Advanced Research Projects Agency, administered by the Department of Defense, to try harnessing power from plankton.
In her lab at OSU's Hatfield Marine Science Center in Newport, Reimers has spent the last four weeks testing the fuel capacity of plankton strained out of the nearby ocean. Using the same principal as the seafloor fuel cells, the researchers thus far are able to direct about 10 percent of the energy associated with plankton decomposition into a usable power source.
The power generated is not large-scale, Reimers quickly points out. But if a free-gliding ocean instrument strained out plankton in its path, it could extend its survey mission for a period of months - or eventually, years - without having to replace a battery. Though it sounds modest, in terms of energy production, the ocean does have a very large capacity for fuel generation.
"Organic matter is the basic fuel of the ocean," Reimers said. "Plankton debris is raining down to the seafloor constantly. Quickly most is degraded naturally, producing carbon dioxide, and a small amount eventually becomes petroleum, natural gas, methane chunks or some other source of fuel. The fuel is there - in the mud, or in the plankton. Our focus is on developing power for oceanographic equipment. Who knows what spin-offs will develop beyond that?"
Reimers did say that the same technology could work if fed other organic substrates, such as sewage sludge.
"You are simply extracting energy by accelerating decomposition," she said.
The process isn't yet perfected. The researchers have to deal with the corrosive nature of seawater on electrical contacts and in the case of the plankton fuel cell, develop an energy efficient means of collection and concentration.
During the next several months, Reimer and her research team will continue to work with their plankton fuel cells in an effort to boost their efficiency.
This October, Reimers will lead a cruise off the Oregon coast where the researchers will deploy eight of the seafloor fuel cell prototypes along the Oregon shelf. These instrumentation packages will be imbedded into the sediment about 20 kilometers offshore for a year and then recovered.
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