It’s unlikely most people think of wastewater as a resource, but a team of researchers at Pennsylvania State University definitely does.
Basically, the team has come up with a way to combine a fuel cell system with another electrochemical process to maximize the amount of electricity that can be harvested from the chemical energy normally generated by wastewater treatment.
The remarkable thing about the potential output of such a system, the research study’s lead author, Bruce Logan, tells Nature magazine, is that domestic waste water contains nine times more chemical energy than the energy required to treat it—almost enough to maintain the entire U.S. water infrastructure. Logan, director of Penn State’s Hydrogen Energy Center and the Engineering Energy and Environment Institute, and his team published their findings this week in Science magazine.
The electricity-harvesting process in this case consists of two systems operating in concert: microbial fuel cells (MFCs) and a process called reverse electrodialysis (RED), in which the salinity gradient between fresh water and seawater is harnessed to generate electricity. An ammonium bicarbonate solution replaces seawater for this particular application because, the researchers say, it significantly boosts the power output of the system.
When microorganisms are introduced to wastewater to oxidize organic matter in MRCs, electrons released during the process migrate to a positive electrode in the MRC while hydrogen ions migrate into a separate cathode chamber. This causes the electrons to surge over a circuit from the positive electrode the cathode. That electron flow is one of the system’s sources of electricity. The RED system, meanwhile, pumps the saline and water solutions across pairs of special membranes, connected to oppositely charged electrodes, that let only positively or negatively charged ions pass through. Again, the voltage and amount of electron flow produced by the process is impressive.
“We are not only getting more power and more voltage, we are also cleaning the waste water faster and better,” Logan says.