[Image above] Credit: WuWu; Flickr BY-NC-ND 2.0

The United States’ approach to power generation just keeps getting greener.

We’re seeing green energy solutions become more economical and mainstream—think solar panels on residential rooftops and wind turbines that supply power to communities across the nation. With each green-energy development, our carbon footprint gets a little smaller.

(Check out three clean energy trends we saw in 2015 thanks to materials science.)

Wind energy is the fastest-growing source of electricity in the world, and harnessing it is one of the cleanest, most sustainable ways to generate power. According to the Department of Energy, wind generation in the U.S. tripled in the past six years and now accounts for nearly 5% of the country’s total electricity across 39 states.

Solar energy solutions give wind power a run for its money, though. Commercialized solar energy use in the U.S. spiked 33% in 2014, thanks to soaring solar industry expansion.

But one form of clean energy that doesn’t seem to make news as often is hydropower.

We’re familiar with mainstream forms of hydropower from sources like rain, melted snow, and rivers. But recently researchers at Virginia Tech have discovered a way to maximize the amount of electricity that can be generated from the wastewater we flush down the toilet, according to a Virginia Tech news release.

Xueyang Feng, assistant professor in the Department of Biological Systems Engineering at Virginia Tech, and Jason He, associate professor of environmental and water resources engineering, got up close and personal with two specific bacterial substrates in wastewater—lactate and formate—and found that the relationship between the two allowed bacteria to produce more energy than either substrate on its own.

This discovery could help researchers understand how electrochemically active bacteria create energy, which could lead to the development of new treatment system called a microbial fuel cell, the release explains.

“Tracing the bacteria gave us a major piece of the puzzle to start generating electricity in a sustainable way,” Feng says in the release. “This is a step toward the growing trend to make wastewater treatment centers self-sustaining in the energy they use.”

The researchers observed that the substrates didn’t perform the same job in the same way. For example, lactate was metabolized by its host bacteria to support cell growth, while formate oxidized to release electrons for higher electricity generation, the release explains. When Feng and He combined these two substrates, they worked in tandem with receptors in fuel cells to produce far greater power than they would separately.

The concept of using microbial fuel cells isn’t new, but “the kind of organics that Feng and He used was novel in generating electricity because they were able to measure the symbiotic nature of two particular organics,” the release notes.

Check out this video produced by Virginia Tech that illustrates the process.

Credit: Virginia Tech; YouTube

He and his team are currently operating a 200-L microbial fuel cell system in a local wastewater treatment plant for evaluating its long-term performance with actual wastes.

As far as current adoption of wastewater energy systems go, Washington, D.C., already successfully uses a process that harnesses energy from wastewater, and the town of Grand Junction, Colo., employs a water treatment plant that uses methane from the solid matter in wastewater to generate energy, according to the release.

The open-access paper, published in Scientific Reports, is “13C pathway analysis for the role of formate in electricity generation by Shewanella oneidensis MR-1 using lactate in microbial fuel cells” (DOI: 10.1038/srep20941).