OSU Researchers Tap Plankton Power

By Tiffany Straza

It may be smelly, but rotting turns out to be a useful source of energy.

Tapping into the decomposition process of tiny marine organisms can produce electrical power in specially designed fuel cells. No energy from a battery or motor is necessary; indeed, the gadgets are "called fuel cells because the fuel is renewed and supplied from the outside,” says Clare Reimers, professor of oceanography at Oregon State University (OSU).

Reimers was lead author in 2001 for a publication detailing seafloor fuel cells, which are partly embedded in the sediment. Now her group has made a prototype fuel cell to use plankton decomposition in the water column between the surface and seafloor, or the pelagic zone.

This technology is helpful for "extending the time instruments could be out monitoring in remote parts of the ocean,” says Reimers, so that "you'll get longer and better datasets.” Self-sustaining power generation would enable scientists to deploy equipment autonomously, without cables to a ship or huge battery supplies. Sustainable, ‘clean' power sources would not only be easier, but also more cost-effective and environmentally-friendly.

The cells use natural processes: when plankton die, microbes feast. The microbes digest the organic matter that once was plankton, creating chemical species that are enriched with exchangeable charges (electrons). This build-up of charges creates a voltage gradient in the fuel cell, just like the gradient in a battery. In lab tests so far, the pelagic cell prototypes can convert around ten percent of the decomposition energy into usable electricity in a four-liter pelagic fuel cell.

Some microbes actually attach to the electrodes and shuttle charges directly into the system. Certain types are better at this, and "we are not just exploiting the power that comes from microbes, but we are also learning about them as we go along,” says Peter Girguis, a collaborator on the project. Once a population of microbes has attached to the electrodes, all that is needed is food for them. Concentration of the plankton into the fuel cell is necessary for enough electricity to be generated. A mobile cell, like a robot, gliding through the water could ‘scoop' plankton out of the water in a sort of sieve system.

Plankton is fairly dilute in the ocean, and ensuring that there is enough to ‘feed' the cell is one of the challenges to this technology. Potential solutions include placing sensors on the robot to detect areas of high plankton abundance. If the amount of plankton available is not constant enough to generate sustained power, equipment may be designed to switch to supplemental batteries, and at least the batteries would have to be replaced or recharged less often. But if the cells generate too little power, they are no more cost-effective than just batteries. Pelagic fuel cells have not yet been tested in either mode outside the laboratory.

The fuel cells, so far, seem to be fairly environmentally benign, since no new processes are introduced. The seafloor fuel cells were noted to affect the surrounding area on a scale of tens of centimeters, by shifting the types and abundances of microbes. According to Girguis, "the few deployments we've done are no more detrimental to the seafloor sediments than rocks. The bigger concern is the materials we use, like plastics. We should be mindful not to leave that on the seafloor.”

This research is funded by the Defense Advanced Research Projects Agency (DARPA). Ed Carapezza, DARPA technical program manager, says "harvesting energy from naturally occurring materials and processes in the oceans of the world will significantly improve our knowledge of both physical and biological oceanographic conditions and processes and will improve our national defense and homeland security capabilities by enabling a near continuous surveillance in the highly dynamic oceans and coastal areas of the world."

Tiffany Straza is an undergraduate senior in oceanography at the University of Washington.