Traditional and Biomimetic Membranes for Water Purification

In the current state of water desalination, highly energy intensive sources such as oil or the electric grid are required to push water through a membrane to remove salt. If the membranes that are used in the desalination process could be made more efficient, a less energy rich method, such as solar energy, could be used. This could have a great impact in under-resourced regions of the globe. This is one of the goals that chemical engineering‘s Manish Kumar has set for himself and his group.

Kumar’s group is conducting fundamental research on existing membranes to see how they can be improved, while also working on the next generation of membranes. Their primary focus is trying to make clean water available in a more energy efficient manner to those without access to high-quality water.

“Membrane technologies are already becoming big in developing countries and have been important in developed countries for some time now. It’s just that it takes a lot of energy to push water through a desalination membrane,” Kumar says. “If we can make the technologies I’m working on cheap enough to be implemented, it could be a very simple way of treating water.”

Bioinspired biomimetic membranes

The best membrane for removing minerals from salty water may be the very one that nature has worked on for a billion years or so to protect the cells in our bodies, Kumar says. Nothing engineers have yet developed matches the filtration system of the cellular membrane.

Aquaporins are proteins that transport water through channels in the membranes of biological cells. This protein transports water at about the same rate as one candidate filter, carbon nanotubes. Both aquaporins and carbon nanotubes can transport billions of water molecules per second, but only aquaporins can reject sodium and chloride (salt).

This protein can be taken out of the cell membrane and grown in large numbers in bacteria or yeast. Then they can then be removed from the growth medium and put into a polymer membrane to do filtration that cannot, as yet, be done with synthetic materials.

In 2015, Kumar and colleagues at Penn State and several other university labs synthesized, modeled, and characterized a bioinspired artificial water channel that can self-assemble into arrays in membranes. Based on the structure of the aquaporin protein, this synthetic organic structure has the same high transport rate but not the salt rejection capability that aquaporin has. These next generation synthetic water channels were assembled into highly packed planar membranes as a first step toward developing scalable engineering applications for liquid and gas separation. With modification of the channel pore size, these artificial aquaporin could be functionalized for water desalinization, Kumar believes. Earlier this year, he received a prestigious National Science Foundation CAREER award and five years of research support for this work.

A water engineer

Kumar’s background has revolved around water since his undergraduate days in India, where he worked on membranes and ion exchange for water treatment. In graduate school at Illinois, he looked at membrane fouling while earning a master’s degree in environmental engineering. From there he moved to industry, working on ways to scale up new membranes to industrial uses and helping to install membranes in utilities.

After nearly seven years in industry, Kumar decided to pursue a Ph.D. in a new area, using ideas from biological cell membranes as water treatment membranes again at Illinois. A post-doc at Harvard Medical School led to the study of a protein that conducts water transport in the eyes – aquaporin 0.

“I consider myself a biomimetic materials engineer, but I tell my kids I’m a water engineer, because I’ve worked so long in the water industry and feel very connected to this aspect of our work.”

Kumar collaborates with a large number of Penn State colleagues on various areas of water treatment and membranes. With chemical engineer Andrew Zydney, he works on frack water treatment. With biochemist Tom Wood, he works on biofilm fouling on membranes. Darrell Velegol, another chemical engineering colleague, and Kumar study how to keep membranes clean from fouling by small colloids and small particles. He also collaborates with Michael Hickner in materials science and engineering on frack water treatment and with Enrique Gomez (Chemical Engineering) on the microstructure of desalination membranes.. A large group of chemists, chemical engineers, and bioengineers at Penn State work in the area of biological and bioinspired membranes. Among them, Kumar collaborates closely with Peter Butler (Biomedical Engineering) and Paul Cremer on membrane protein dynamics in biomimetic membranes.

“If you are talking about membranes, we are really one of the best schools in the country,” Kumar says. “There are lots of papers written at Penn State in this area, and a variety of top-of-the-line instrumentation that very few universities have.”

Ready, Campers?

Another collaboration is with Chris Gorski, a civil and environmental engineer in Penn State’s College of Engineering. Together the two engineers run a water camp each summer at Penn State for middle schoolers in conjunction with Science-U, a program of the Eberly College of Science that immerses thousands of young people in the experience of scientific discovery. Their full-week hands-on water camp teaches students about the whole water system and how it affects them, including water conservation, water treatment, and how water distribution works.

“That’s a really fun thing we do with Science-U,” he says.

Manish Kumar is assistant professor of chemical engineering.

Contact him at manish.kumar@psu.edu. His research website can be accessed at www.kumarresearchgroup.com.

Faculty/Research Experts: 
Kumar, Manish