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Arsenic-removing material wins U.S. patent and moves into marketplace

The Valencia Water Co. in Buckeye, Arizona, uses the materials invented by Arup K. SenGupta and Luis H. Cumbal to remove arsenic from drinking water.

Two Lehigh engineers have received a U.S. patent for an invention that uses a hybrid polymeric and inorganic material to remove arsenic, a highly toxic and carcinogenic element, from groundwater.

The invention, a hybrid anion exchanger sold under the trade name ArsenXnp, is now being used in more than 300 installations in nine states in the U.S., and also in the countries of Hungary, India, Brazil and Ecuador.

The patent for the technology was awarded to Arup K. SenGupta, a professor in Lehigh’s departments of civil and environmental engineering and also of chemical engineering, and Luis H. Cumbal, who earned a Ph.D. in environmental engineering from Lehigh in 2005. Cumbal is now professor and director of graduate studies at the Army Engineering Polytechnic School in Quito, Ecuador.

ArsenXnp is licensed to SolmeteX Co. in Northborough, Mass., and manufactured by Purolite Co. of Philadelphia.

ArsenXnp is a hybrid material consisting of ferric-oxide (iron) nanoparticles dispersed by an anion exchanger throughout a polymer-based bead. The nanoparticles selectively adsorb (bind or attach to the surface of) arsenic as well as phosphate, vanadate and other contaminants.

The relatively large surface area of the nanoparticles enhances their reactive capabilities. The particles can also be regenerated and reused. And the chemicals used in ArsenXnp are environmentally benign.

More than 300,000 people in the U.S. now drink arsenic-safe groundwater that has been treated by ArsenXnp, says SenGupta. These include residents of mobile homes, mobile home parks and single-family homes. The technology, says SenGupta, is flexible and has been used in applications ranging from individual houses to schools to municipalities treating more than 3 million gallons of drinking water per day.

Global arsenic crisis

The most noteworthy application of the technology invented by SenGupta and Cumbal has been in Eastern India, home to the world’s worst arsenic contamination, where, with the help of engineers from Bengal Engineering and Science University, arsenic-removal systems have been installed in the water wells of more than 150 villages.

Arsenic levels in those wells have fallen from 100 to 500 parts per billion to below the 50-ppb maximum allowed by the Indian government. Victims of arsenic poisoning have found relief from their symptoms, which include skin lesions, tumors and cancer, and reports of new cases of arsenicosis have plummeted.

The World Health Organization estimates that as many as 100 million people in Eastern India and neighboring Bangladesh drink water containing toxic levels of arsenic. WHO calls the phenomenon the “largest mass poisoning of a population in history.”

For their efforts in India, SenGupta and Cumbal and their colleagues last year received the $200,000 Silver Award in the National Academy of Engineering’s Grainger Challenge for Sustainability. The prize was shared with the nonprofit organization Water for People and also with John Greenleaf, a Ph.D. candidate in environmental engineering; Lee Blaney ’05, a graduate student in environmental engineering; Owen E. Boyd, CEO of SolmeteX Co.; and Arun K. Deb, retired vice president of Weston Solutions Inc. in West Chester, Pa.

A historical significance

ArsenXnp is the first hybrid ion exchanger (HAIX) to intentionally exploit the 100-year-old Donnan effect and attain enhanced sorption of arsenate, arsenite, phosphate, chromate and other ligands, SenGupta says. (A ligand is an ion, molecule or molecular group that binds to another chemical entity to form a larger complex.)

The Donnan effect, named for the British chemist Frederick G. Donnan (1870-1956), refers to the failure of charged particles to distribute evenly across the two sides of a nearby semi-permeable membrane.

“HAIX is essentially an anion exchanger within which hydrated iron oxide nanoparticles have been irreversibly dispersed,” says SenGupta.

“The synthesis of HAIX posed a major scientific challenge because the positively charged ferric ion [Fe3 ] is strongly rejected by an anion exchanger with a positively charged quaternary ammonium functional group [R4N ].

“The challenge was overcome through a novel synthesis process that was subsequently scaled up for large-scale production. Very large amounts of hydrated Fe(III) oxide nanoparticles (nearly 25% by mass) can now be introduced within a anion exchanger.”

HAIX particles, says SenGupta, are not homogeneous at the microscale, but instead remain heterogeneous down to the level of 10 nanometers, where the simultaneous presence of quaternary ammonium functional groups and Fe(III) oxide nanoparticles in close proximity create a synergy resulting in high sorption capacity and excellent kinetics.

SenGupta and Cumbal worked more than a year before they succeeded in preparing 2 grams of hybrid anion exchanger and dispersing iron oxide nanoparticles in 2003. Since then, they have refined and scaled up the process of synthesizing and dispersing the nanoparticles. Today, an estimated one million pounds of the hybrid nanosorbent is being used in nine U.S. states—Arizona, New Hampshire, Nevada, California, New Mexico, Connecticut, Maine, Michigan and Oregon—to remove arsenic from groundwater.

SenGupta has received partial funding for the arsenic-removal project from the Pennsylvania Infrastructure Technology Alliance.

--Kurt Pfitzer

Posted on Tuesday, May 06, 2008

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