A research project at a Virginia treatment facility looks at the energy generation potential of a microbial fuel cell.
It takes a long time to develop new technologies. The hydrogen fuel cell, now growing in popularity at wastewater treatment plants, was invented in 1839.
But it would take until the 1960s before NASA became the first to use them in a real-life application, generating electricity and water for manned space flights, and many more years before the technology came to the market.
“The government invested so much money, and it still took 40 years for the hydrogen fuel cell to be commercialized,” says Jason He, associate professor of civil and environmental engineering at the Virginia Tech College of Engineering. He’s been working on a similar technology for 12 years.
The microbial fuel cell both cleans wastewater and uses electrons released during the digestion process to generate electricity. A small version is now being tested at the 9 mgd (design) Pepper’s Ferry Regional Wastewater Treatment Authority in Radford, Virginia.
A microbial fuel cell is designed to capture electrons released as organic material breaks down, according to He: “A hamburger is an organic compound. When food digests in our body, it releases electrons through oxidation.
“In regular anaerobic digestion, the electrons are stored as methane, so we get biogas. A microbial fuel cell is a similar process, except that we put in electrodes so we can harvest the electrons and get electricity. That’s one of the major benefits of this technology, the direct generation of electricity.”
The challenge with wastewater is the relatively low organic loading. “When you use a pure substrate like glucose, you get very high efficiency, 60 to 80 percent of the organics converted to electricity,” says He. “It’s much lower when you use wastewater, around 20 percent.”
When he first began exploring the technology, He thought the fuel cell would compete with anaerobic digestion. He now thinks the two can help each other when dealing with higher-strength wastewater. A niche for the microbial fuel cell, however, is probably low-strength wastewater.
“If you have BOD lower than 1,000 mg/L, an engineer probably won’t recommend anaerobic digestion,” he says. “We would look at aerobic treatment like an activated sludge process. In this area, microbial fuel cells could be a competitor.”
He began his microbial fuel cell project while serving as an assistant professor in the Department of Civil Engineering and Mechanics at the University of Wisconsin-Milwaukee from 2009 to 2013.
A small version of the reactor was tested at Milwaukee Metropolitan Sewerage District’s 300 mgd South Shore Water Reclamation Facility in 2012. The 4-liter system operated for 450 days using primary effluent from the plant’s settling tanks and demonstrated the capability to treat wastewater and recover energy with low biosolids production and low energy consumption.
It was enough to convince He to scale up his test, and he has done so since he moved to Virginia Tech in 2013. A 200-liter system has been in use at Pepper’s Ferry for more than a year with help from a National Science Foundation grant.
Electrical production in the South Shore project was low and variable, depending on conditions such as organic concentrations, conductivity in the primary effluent, and air temperature (the system was set up in an unheated room). Production was generally around 0.02 kWh per cubic meter of treated wastewater, but did show a positive energy balance.
In the Pepper’s Ferry research, electrical production was less then theorized, just below 0.01 kWh per cubic meter. But it made enough to operate a 60-watt DC recirculation pump periodically. There was a slight positive energy balance at lower recirculation but a net energy loss at higher rates. Again, many variables were in play in the design of the system and the ways it was used during the testing.
The results still indicate to He that the microbial fuel cell is a promising wastewater treatment alternative: “Although electrical production is low, electrical consumption is very low. We now see the major advantages being lower energy consumption and low sludge production.”
Getting to market
His project is approaching the difficult point all new ideas eventually reach — bridging the gap between concept and commercial product. “Commercialization is always a big challenge,” He says. “There are limitations for university researchers. I only have my students to make the 200-liter system in the lab. It was tough.”
Having taken the concept from the lab to bench testing to the transitional testing phase at Pepper’s Ferry, he is now waiting for a proposal to take the next step to build a research project about twice the size.
After that, it would be time for a full pilot project. That will probably happen in about five years, and He says it will definitely require an industry partner. He estimates that a full-scale system would have capital costs comparable to a small wastewater treatment plant. “It’s a new concept so there’s high risk, obviously.”