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ORONO — Onur Apul, an assistant professor of environmental engineering at University of Maine, will lead a $1.1 million multi-institutional investigation backed by NASA to explore whether nanobubbles can support space exploration, including water treatment on spaceships.
Through the Maine Space Grant Consortium, NASA Established Program to Stimulate Competitive Research awarded the project $753,750 grant. It was matched with a $350,000 cost share contribution provided by participating institutions, which included UMaine, the University of Southern Maine and Arizona State University.  
Nanobubbles are ultrafine pockets of oxygen, carbon dioxide, hydrogen and other gases in liquids that have diameters smaller than 100 nanometers. Apul, says nanobubbles can be generated in liquids with simple instruments that oscillate liquids and through other hydraulic, physicochemical and electrochemical methods. This results in mixtures known as biphasic liquids — those that take the forms of both a liquid and gas.
Apul says due to their size, nanobubbles possess unique physicochemical properties that he believes may improve the efficiency of life support functions on spaceships, particularly water treatment and growing algae to provide oxygen and nutrition for astronauts. Unlike regular bubbles that float to the surface of a liquid, nanobubbles can suspend in it for hours, days or even months. Apul says they also possess a high surface area and high reactivity, but are also malleable, making them ideal for chemical reactions. All of these aspects allow nanobubbles to provide reliable and accessible storage for various gases, which Apul says supports and reduces the energy cost of water treatment and other systems on earth and possibly in space.  
To determine whether nanobubbles can benefit life support systems beyond Earth’s atmosphere, Apul and his team must ensure they can withstand micro- and zero gravity, as well as the conditions of fluids in those environments. Their research will focus on nanobubbles of oxygen, hydrogen, nitrogen, ozone and other atmospheric gases. Additionally, they will evaluate how well nanobubbles enhance mass gas transport, which would increase the efficiency of water treatment systems, and produce reactive oxygen species that could fuel algae growth.  
Researchers will first generate their own nanobubbles in biphasic liquids with existing and new equipment at UMaine. They will then test their stability in a high altitude balloon, which can travel up to 118,000 feet or more, through UMaine’s High Altitude Ballooning Program; a small research satellite called a CubeSat, and in two rocket launches. The company blueShift Aerospace Inc. in Brunswick, Maine will work with researchers on the launches for the CubeSat, which will be called PINESAT2 and be built at the WiSe-Net lab in the UMaine Electrical and Computer Engineering Department, as well as the two rocket launches, Apul says. One rocket will travel 62 miles and another will ascend 186 miles.
Eventually, researchers hope to test their biphasic liquids with nanobubbles by sending them to the International Space Station, Apul says.  
“It’s very theoretical now, but we believe this could shift the paradigms of using gases in unconventional situations,” Apul says. “This is a novel research area that is only 10 years old, and the potential it has is exciting. My slogan for them is ‘tiny bubbles, massive potential.’”
The project team includes Apul, Ali Abedi, UMaine associate vice president for research and professor of electrical and computer engineering; Sergi Garcia-Segura; assistant professor of environmental engineering at Arizona State; and Ashanthi Maxworth, an assistant professor of environmental engineering at USM. They will collaborate on the project with researchers from NASA’s Johnson Space Center.
Apul has been studying nanobubbles for two years and worked with various stakeholders interested in their development, including a distillery in Texas. Some of his students also are involved in nanobubble research. One of them, Zach Doherty, a graduate student of civil and environmental engineering, received the Susan J. Hunter Presidential Research Impact Award in the 2022 UMaine Student Symposium as a fourth-year undergraduate for his investigation of the use of nanobubbles to remove drinking water pollutants. Joseph Patton, a Ph.D. student with the UMaine Electrical and Computer Engineering Department who worked with Abedi to develop MESAT1, Maine’s first CubeSat, also is involved in this project and is leading CubeSat development for it.
The new study will help answer fundamental questions about nanobubbles, after which researchers can springboard into investigating other possible applications for them on Earth and beyond, Apul says. Nanobubbles might even serve industries important to Maine, such as aquaculture and pulp and paper manufacturing.
Three Ph.D. students, two in Maine and one in Arizona, and three-to-five undergraduate researchers are expected to work on the study. New equipment purchased through this research will complement existing tools and expand the capacity for scientists at both UMaine and USM to investigate nanobubble production, characterization and application, Apul says.
“We are creating the infrastructure, the backbone, for nanobubble research in Maine,” he says. “This is only the beginning of it.”

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