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Bruce Logan wants to tap the power of sewage–and so far, he’s succeeding.
Logan, a professor of environmental engineering at Pennsylvania State University has created shoebox-size devices that can use the power of sewage to light a bulb or spin a fan. But if his devices can be scaled up effectively, electricity could one day flow from the sewage treatment plant at the edge of town.
In the United States, about 5 percent of all the electricity we generate is used to move clean water to municipal drinking water plants, and to move wastewater to sewage treatment plants and to treat it. All told we use between 20 and 30 gigawatts—the equivalent of 20 nuclear power plants—to push, pull and pump that water around, Logan said.
Yet “there’s energy in that wastewater,” Logan said. A full 17 GW, in fact—almost as much as we use to pump and treat it. Wastewater is full of energy-rich organic material. Microbes take advantage of it, growing on and in sewage by the billions, but for the most part humans don’t. There’s no reason, however, that they can’t, Logan said during a presentation at a science writers’ conference in Raleigh, North Carolina, earlier this week.
Logan has spent most of his career investigating how to ensure the world is able to sanitize its sewage. “We can, but that takes energy,” he says. And since most energy comes from fossil fuels, “the more energy you use, the more you have to think about climate change.”
To find a way around that dilemma, Logan tried to think about the problem differently. Specifically, he said, “I started to think about water and how water might be a solution for energy.”
It turned out that just as we breathe oxygen, there are microbes in wastewater that can breathe minerals. And when they do, they generate electricity.
In other words, just as the cells in our tissues transfer electrons to oxygen, these microbes can transfer electrons to metals, either in a rock or in a wire. Logan has built two types of devices—fuel cells in which the microbes help generate electricity, and electrochemical cells in which the microbes help generate hydrogen.
During his presentation, Logan showed a video of a shoebox-sized device in which, he said, electricity from microbes feeding was spinning a small fan. Inside the device, called a microbial fuel cell, are the elements of any battery—a positively charged anode and a negatively charged cathode, separated by an insulator. However, the anode was coated by a film of microbes and exposed to circulating wastewater.
The microbes in that film eat the organic matter in the wastewater to grow, passing on electrons to the metal in the anode. Since the anode is insulated from the cathode, excess electrons move around a circuit, generating electricity.
Since developing the device, Logan has brought its cost down to one-fiftieth the original cost by building it with cheaper materials. He’s also devised ways to stack multiple microbe-covered electrodes like pancakes. This creates more power in the circuit, just as a flashlight with three batteries stacked end to end has more power than a battery with one.
Logan has also created related devices called microbial electrolysis cells that use microbes to produce hydrogen rather than electricity. At the meeting, he described a pilot scale test of one such device that held 1,000 liters of waste from a winery in California’s Napa Valley.
“All in all the experiment was successful in making energy,” Logan said. “It made more energy than we put into the reactor.”
Between microbial fuel cells, microbial electrolysis cells, and several other related technologies, “we have the microbes that could create a whole new energy platform for us,” Logan says.
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