Microbial Fuel Cell Cleans Wastewater, Desalinates Seawater, and Generates Power

Desalinization technology has long been trapped between two competing nightmare scenarios. Without desalination, fresh water resources run out and large swaths of the earth suffer crippling water shortages. But if we desalinate on a large scale, we keep burning fossil fuels, the earth warms, the ice caps melt, and sea levels rise to wreak havoc on coastal regions.

Desalinization could theoretically solve the impending water crisis if it weren’t such an energy-intensive process; desal requires large amounts of electricity, which is primarily generated by burning fossil fuels. Call it a catch-22. But researchers at Penn State think they’ve solved the problem by creating a process that cleans wastewater while generating electricity, simultaneously removing 90 percent of salt from seawater.

Current desal methods — which either employ reverse osmosis to push high-pressure seawater through salt-extracting membranes, or electrodialysis to pull ions out of water using electricity — require a great deal of power. The Penn State team has sidestepped the problem by custom-tooling a microbial fuel cell to desalinate saltwater. While the system is not yet optimized (it currently uses 200 milliliters of wastewater to desalinate 3 milliliters of saltwater), the fact that it’s possible could spell a breakthrough in sustainable technology.

Microbial fuels cells convert chemical energy to electrical energy by tapping the electron exchange between two chambers. In the anode chamber, oxygen-starved organic material — in this case, wastewater — is oxidized by naturally occurring bacteria (though researchers are genetically tooling even more efficient bacteria in labs). This releases protons and electrons, from which the fuel cell extracts electrical power. The researchers placed a third chamber in between the anode and cathode, separating the central chamber from the other two with ion-specific membranes that allow either positive or negative ions to pass, but not both.

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