NEWS | Feb. 25, 2013

NRL Researcher Discusses Benthic Fuel Cells, Electricity from Wastewater, and Fuel from CO2

By Daniel Parry

Research chemist and branch head at the Center for Bio/Molecular Science and Engineering at the U.S. Naval Research Laboratory (NRL), Dr. Lenny Tender, speaks with Department of Defense Armed with Science on cutting-edge research to address the growing concerns of carbon-based energy consumption and the reduction in carbon dioxide (CO2) emissions.

Co-inventor of the microbial fuel cell (MFC), which persistently generates electrical power in marine environments, Tender is an internationally recognized leader in MFC research that spans implications in alternative, carbon-neutral energy generation that address pressing needs of the Navy, Department of Defense (DoD), and the nation.

To get long-term data on the state of the oceans is very difficult because oceanographic sensors are constantly running out of battery power. What the benthic fuel cell does is generate electricity indefinitely using microorganisms naturally residing on the sea floor.

At the bottom of the marine environment we have sediment, the mud at the bottom of a harbor, river, lake, or the ocean, which has quite a bit of fuel in it, organic matter which microbes draw upon to satisfy their energy needs, Tender says. You can think of anything that has ever lived in the marine environment, phytoplankton, sea creatures, etc. When they die, they settle on the sea floor and, like leaves on the lawn, start decomposing—and this represents a pretty potent fuel source for marine microorganisms to produce energy in the form of electricity.

There are thousands of oceanographic instruments that are deployed every year by the Navy. Naval fleets around the world, science organizations, and academic researchers studying climate get a relatively short picture of what is occurring over time. This is due to the limited lifetime of batteries typically used to power oceanographic instruments. In comparison, the benthic MFC can operate indefinitely, owing to the immense reservoir of fuel and oxidants that it draws upon in the marine environment.

Tender's research in benthic MFC development, therefore, has significant implications to future Navy capabilities with respect to persistent in-water Intelligence, Surveillance, and Reconnaissance (ISR) operations for warfighters in riverine, estuarine, and close-in littoral environments.

With funding from the Bill and Melinda Gates Foundation, Tender has expanded his MFC research to include wastewater treatment. Whereas conventional treatment processes consume significant power—an issue that confronts the DoD and developing countries alike—MFCs may enable power generation from wastewater treatment.

As Tender describes, approximately five percent of U.S. electricity consumption goes to treating wastewater. The inherent energy represented by the organic matter, which is the fuel in the wastewater, can instead be used to generate electricity. Expanding on this idea, Tender says, this provides an opportunity to flip that equation upside down and to actually think of wastewater treatment plants as power stations.

The funding we have with the Gates Foundation is to help Third World communities. In other areas of the world, most don't treat wastewater, so people can get very sick. If we can come in and say 'well, not only can we treat the wastewater, but knock down the prevalence of disease and provide you with electricity,' that's the interest of the Gates Foundation that holds a similar interest to that of the DoD.

Tender describes other applications stemming from this research that he says will go way beyond just generating energy on the sea floor. One of the things my team and I are pursuing now, that I'm very excited about, is the idea of using microorganisms as catalysts on electrodes to generate fuel from carbon dioxide, Tender said. This is an opportunity to start drawing on the carbon dioxide that's already in the atmosphere and generating a fuel, basically running the combustion process in reverse.

In the case of his microbial fuel cell, microbes oxidize organic matter residing in marine sediment or wastewater and transfer the acquired electrons to the anode. This results in the generation of electrical power, but also carbon dioxide. By running the process in reverse, it is possible to use microbes to reduce carbon dioxide back into forms of organic matter that can serve as transportation fuels, using electrons donated from cathodes and solar-generated electricity. However, the trick, says Tender, is finding candidate microbes that are very good at accepting electrons from cathodes and reducing carbon dioxide—components that he says his team has already identified.

For Tender, the benthic microbial fuel cell has opened up an entire line of research that he believes will have a much higher impact than powering oceanographic sensors on the sea floor. To view the interview video in its entirety, please visit the official page of the U.S. Naval Research Laboratory on YouTube.