NM Tech Researcher Develops Effective Filtration System for Saline Waters

by George Zamora

[Note: for more information, or to collaborate on marketing this new technology, please contact Dr. T. M. Whitworth, (505) 835-5921, mikew@nmt.edu or Alex Thyssen, (505) 835-5658, athyssen@admin.nmt.edu.]

SOCORRO, N.M., June 14, 1999 -- There are an estimated 20 billion acre-feet of groundwater stored beneath New Mexico's arid surface, yet only about 3 billion acre-feet can be recovered as potable fresh water. The rest is too salty for human consumption.

The conventional water-purifying process of reverse osmosis--whereby water is forced under high pressure through membranes which act as molecular-scale filters--has shown great promise of providing an economical method of removing dissolved salts and other mineral impurities from "impaired" waters, but reverse osmosis is hampered by the relatively large waste stream produced.

In some applications, the waste produced from the reverse osmosis process can be as much as 80 percent of the total volume of water being treated.

The high cost associated with disposing of all those wastes, therefore, becomes a limiting factor.

In hopes of providing a solution to the waste disposal problem associated with using reverse osmosis, a New Mexico Tech researcher has been exploring the possibility of converting the resultant liquid waste stream into a solid, resulting in a substantial reduction of the total volume of waste products produced--as little as a thousandth of the previous volume--as well as a subsequent reduction in waste disposal costs.

Dr. T. M. "Mike" Whitworth, a chemical hydrogeologist with the New Mexico Bureau of Mines and Mineral Resources, currently is conducting research into combining a standard reverse osmosis system with a low-cost, low-efficiency membrane filtration system to efficiently remove the salt in solid form from saline waters.

By using his innovative filtration system in past related research efforts, Whitworth has successfully precipitated heavy metals, including copper, cobalt, and lead from solutions which are forced through clay membranes--a process called"hyperfiltration."

His current research now focuses on using that same hyperfiltration method to precipitate sodium chloride, or salt, a common constituent of almost all waters.

"A unique aspect of this research is the possibility of using natural clays as membranes," Whitworth says. "Thin layers of clays have excellent membrane properties and work well for this type of application. Also, clay membranes are very economical in comparison to conventional membranes."

Clay membranes are actually considered inefficient when compared to other membranes used for industrial purposes, but the upside of that property is that they also require very low pressure to achieve adequate separation efficiency for Whitworth's purposes.

Potential uses of the hybrid reverse osmosis/hyperfiltration system are many, Whitworth says.

"A rancher with bad well water might be able to install a clay-membrane hyperfiltration cartridge under the sink and only have to replace it once a year," Whitworth relates. "Or, you could use a larger unit--which would still be relatively small compared to any other competing systems--for filtering out water coming out of a well head. . . . For the most part, with this new system, you could just put out the waste it generates along with the rest of your trash."

The reverse osmosis waste reduction system could also be used by either individuals or municipalities in the treatment of irrigation and river waters to reduce total dissolved solids or to remediate impaired waters.

"With the right setup, I could probably precipitate any metal or mineral from groundwater that you'd want to," he adds, in reference to possible mining applications for the system.

As a continuation of his current research project, Whitworth also is preparing to investigate the use of other materials in place of the natural clays he now uses in his systems.

Whitworth's research on using hyperfiltration systems to remove salt from groundwater is funded in part by New Mexico State University's Water Resource Research Institute (WRRI) and the Waste-management Education and Research Consortium (WERC).

New Mexico Tech has filed a patent application on this invention and currently is looking for industrial collaborators to market the new technology.

[Note: for more information, or to collaborate on marketing this new technology, please contact Dr. T. M. Whitworth, (505) 835-5921, mikew@nmt.edu or Alex Thyssen, (505) 835-5658, athyssen@admin.nmt.edu.]