Guest Blog: Bug Batteries!

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The last piece of equipment to be deployed on Leg 3 was the CH4-BMFC, which is a collaborative project between Oregon State University and Harvard University, funded by the Office of Naval Research. You may be wondering about the meaning of this long and somewhat bizarre acronym! CH4 is the chemical formula for methane, which bubbles out of the seafloor at Hydrate Ridge in patches that are constantly moving and often hard to find. Along with some other energy-rich compounds, methane serves as a “fuel” to support a large biological community that relies on the ability of microbes to use this compound for energy.

The 2019 OOI digital still camera at Southern Hydrate Ridge (770m) observing a plume of methane bubbles streaming out of the seafloor (on the left side of the image). Credit: UW/NSF-OOI/WHOI, V19

The “BMFC” part of our acronym stands for “benthic microbial fuel cell,” which essentially operates like a battery—only this battery is powered by microbes that obtain energy from compounds emitted from the seafloor. Similar to the batteries you are familiar with, there are two parts to the BMFC: the anode and the cathode. The anode is pushed into the seafloor sediment (“benthic” is the scientific word for “living on the bottom of the ocean”), and the cathode is exposed to oxygenated seawater. Some of the microbes in the sediment are able to use compounds like methane for energy, and rather than transfer electrons directly to oxygen (like we humans do when we breathe), they can deposit them onto a solid material that is in electrical contact with the cathode. This electrical current is captured, stored, and used to charge batteries onboard the BMFC.

The Oregon State/Harvard benthic microbial fuel cell (CH4-BMFC) sitting on a white bacterial mat at Southern Hydrate Ridge (770m). The anode is in the sediment, and the cathode is the black “feather boa” on the vertical component. Credit: UW/NSF-OOI/WHOI, V19

This recent deployment is unique because we specifically targeted a methane seep in order to evaluate whether increased concentrations of methane result in an increase in power production. We’ve also incorporated some additional equipment to monitor the chemical environment within and around the BMFC over the next year, including methane sensors and fluid samplers. After recovery, we will be extracting DNA from the anode and cathode to identify the microbes present in each part of the BMFC. We hope that all of this data combined will provide better insight into the optimal environment for power production.

Microbially-fueled batteries are of special interest to us as oceanographers, because 1) they provide an opportunity to study the unique metabolic capabilities of microbes living at the seafloor, and 2) they have the potential to power long-term sensors in the deep ocean, without the need to be recovered and recharged. However, this technology could also be used in other environments/for other applications where access to electricity is limited. The possibilities for use of microbe-powered batteries are endless!

By: Jennifer Delaney (Harvard University)

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