Salt-Powered Battery to Energize Wastewater Plants


Private research institution Stanford University recently announced the development of a new technology, intended to make coastal wastewater treatment plants both energy-independent and carbon neutral.

A paper on the development has since been published in American Chemical Society’s ACS Omega.

The Battery

According to the university, wastewater treatment accounts for about 3% of all the United States’ electricity. Unfortunately, the process is vulnerable to shutdowns on power grids even though it is essential to community health.

To avoid blackouts and to cut electricity use and emissions, research was launched into what is being called “Blue Energy,” as it generates energy from places where saltwater and freshwater collide.

For every cubic meter of freshwater that mixes with seawater, roughly .65 kilowatt-hours of energy is produced—enough to power an average American household for about 30 minutes. On a global scale, if all coastal wastewater treatment plants recovered said energy, the power would equal to 18 gigawatts, or enough to power more than 15 million homes continuously.

In a news story from Stanford, the battery idea originated with study coauthors Yi Cui, a professor of materials science and engineering, and Mauro Pasta, a postdoctoral scholar in materials science and engineering at the time of the research.

However, applying the concept to coastal wastewater treatment plants was proposed by other coauthor Craig Criddle, a professor of civil and environmental engineering known for interdisciplinary field projects of energy-efficient technologies. Criddle also has a track record for developing technologies specifically for wastewater treatment.

“Blue energy is an immense and untapped source of renewable energy,” said study coauthor Kristian Dubrawski, a postdoctoral scholar in civil and environmental engineering at Stanford. “Our battery is a major step toward practically capturing that energy without membranes, moving parts or energy input.”

Tapping into salt gradients, the battery works by releasing sodium and chloride ions from the battery’s electrodes—made with Prussian Blue (costing $1 per kg) and polypyrrole (costing $3 per kg)—into the solution, creating a current flow from one electrode to another. What happens next is a rapid exchange of wastewater effluent with seawater that leads the electrode to reincorporate sodium and chloride ions and reverses the current flow.

Because energy is recovered during both freshwater and seawater flushes, the battery can constantly discharge and recharge without requiring external energy input. Although it is not the first-time blue energy has been captured, the university reveals it is the first use of battery electrochemistry instead of pressure or membranes.

What Now

To try out the blue energy theory, researchers tested and monitored a prototype of the battery over 180 cycles, all the while flushing it with alternating hourly exchanges of wastewater effluent from the Palo Alto Regional Water Quality Control Plant and seawater collected from Half Moon Bay.

Although testing showed that battery materials maintained 97% effectiveness in capturing the salinity gradient energy, in order to discover the battery’s full potential, the team will need to conduct more research in municipal wastewater plants, or through a scaled version of the test to see how the system performs with numerous batteries working at the same time.

“It is a scientifically elegant solution to a complex problem,” Dubrawski said. “It needs to be tested at scale, and it doesn’t address the challenge of tapping blue energy at the global scale—rivers running into the ocean—but it is a good starting point that could spur these advances.”

Research for this project was funded by the Stanford Woods Institute for the Environment, Stanford’s TomKat Center for Sustainable Energy, the Stanford-based National Science Foundation Engineering Research Center Re-inventing the Nation’s Urban Water Infrastructure, the Stanford Interdisciplinary Graduate Fellowship, the Oronzio and Niccolò de Nora Foundation and the Natural Sciences and Engineering Research Council of Canada.


Tagged categories: Asia Pacific; Blue Energy; Carbon footprint; Colleges and Universities; EMEA (Europe, Middle East and Africa); Energy efficiency; Latin America; North America; Power; Program/Project Management; Research; Research and development; Technology; Wastewater Plants; Z-Continents

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