Howard Stone: Water purification with less energy and no filter

Thursday, Nov 8, 2018

Providing clean water to millions of households could be possible with an invention that purifies water using the same technology that adds fizz to soda. The new approach, developed by Howard Stone, the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering, and his research team, potentially uses less energy than current methods and requires no costly filters.

The technique involves injecting carbon dioxide into a stream of water flowing through a system of channels. The carbon dioxide temporarily changes the water chemistry and causes contaminants to move to one side of the channel depending on their electrical charge. The system then separates the purified water stream from the contaminants.

The researchers have built a laboratory-scale filter and demonstrated that their approach can remove particles a thousand times more efficiently than a conventional microfiltration system. Their system is very simple, requiring a modest amount of energy to pump carbon dioxide into the water and using no filters or membranes.

The carbon dioxide alters water’s chemistry by making it slightly more acidic, resulting in the creation of charged particles, or ions. One of the ions, the positively charged hydrogen atom, moves very quickly through the water, while another, the negatively charged bicarbonate ion, moves slowly. Together the ions set up a slight electric field that attracts contaminants, which have either negative or positive charges of their own, toward either side of the water stream.

Once filtration is complete, the carbon dioxide can be removed simply by exposing the water to air and letting the gas escape, just as it does when soda goes flat.

Using a soluble gas as a method of controlling particles in a solution could lead to other industrial or scientific applications beyond water filtration, Stone said.

“The principles being explored in this research we hope will also be impactful in other research areas.”
-Howard Stone, the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering

Team members: Orest Shardt and Sangwoo Shin, former postdoctoral research associates; graduate students Jessica Wilson and Fan Yang; postdoctoral research associates Suin Shim, Ankur Gupta and Bhargav Rallabandi
Collaborators: Jesse Ault, Ph.D. 2017, and Patrick Warren, staff scientist at Unilever
Development status: Patent protection is pending. A startup company is forming to further develop the technology.
Funding: National Science Foundation, Natural Sciences and Engineering Research Council of Canada, Unilever Research

Contact: John Ritter, Director of Technology Licensing, jritter@princeton.edu or 609-258-1570