As far as sources of renewable energy are concerned, poop would seem a likely candidate as a never-ending supply of fuel.

But it turns out wastewater energy plants stink at maximizing their energy output in a sustainable way.

Nationally, treatment plants consume 5 percent of the country’s total output, but that could be significantly reduced if the plants could harvest the energy from the waste that people flush down their drain pipes every minute of every day.

Two Virginia Tech researchers have discovered a way to harness the energy from wastewater using two distinct methodologies: using a novel tracing technology to determine which bacteria work well together to chew through waste, and also which ones are good conductors of energy.

Xueyang Feng and Jason He traced bacteria, which led them to discover that the working relationship between two specific substrates produced more energy than either did separately. This work will help take the mystery out of how electrochemically active bacteria create energy. It could help in the development of new treatment system called a microbial fuel cell.

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

Feng is in the College of Agriculture and Life Sciences and the College of Engineering; He, an associate professor of environmental engineering, is in the College of Engineering.

The discovery is important because not all organics perform the same job in the same way. Some work because they are food for the electricity-generating bacteria while others are good at conducting energy.

While one substrate known as lactate was mainly metabolized by its host bacteria to support cell growth, another substrate known as formate was oxidized to release electrons for higher electricity generation.

The team found that when these two substrates are combined, the output of energy is far greater than when they are working separately. The organics work in tandem with receptors in fuel cells, and while research using microbial fuel cells is not new, 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 unique methodology that allowed them to trace the metabolic pathways of the different strains of bacteria, called carbon 13 pathway analysis, was the first time this type of isotope labeling process was used in measuring metabolism in microbes, the researchers said. The analysis works by creating a non-radioactive isotope on a carbon group that is visible through a mass spectrometry.

Harnessing energy from wastewater is a sustainability measure that even urban plants such as the wastewater treatment facilities in Washington, D.C.

The results of this work encouraged the further development of microbial fuel cells, especially system scaling up. The He lab is currently operating a 200-L microbial fuel cell system in a local wastewater treatment plant for evaluating its long term performance with actual wastes.

For now, however, Feng and He are not only giving wastewater it’s moment in the sun, they are making sure that, whether it’s ammonia or organic waste, that producing energy from wastewater is part of a movement.

Watch a video here about He and Feng’s discovery.