Nanoparticles remove arsenic from drinking water
A new technology from Idaho National Laboratory promises to reduce the cost of removing arsenic from drinking water.
Researchers at the U.S. Department of Energy’s Idaho National Laboratory (INL) have developed a new material that uses nanosized particles to remove arsenic from drinking water and that promises to be easy to use and to cost less than the current alternatives.
At least three technologies—activated alumina, ion exchange, and coagulation—are capable of enabling utilities to meet the U.S. EPA’s drinking-water standard of 10 micrograms per liter (µg/L) for arsenic, which went into effect throughout the U.S. this past January.
But all of the alternatives come with caveats. For example, activated alumina technology, which is broadly considered to be the best available technology and is also the one most commonly used, works best in the pH range of 5.5–6. It therefore requires utilities to install a pH adjustment unit that can cost a few thousand dollars.
INL’s new technology is made of nanosized polymer beads infused with iron oxide, according to its developer, Troy Tranter. He refused to be more specific about the particle size, claiming that the information is proprietary. Laboratory testing of Idaho groundwater—which contains 20 µg/L of arsenic, a concentration typical for waters in the western U.S.—shows that the technology can remove 100% of the arsenic.
Both INL’s new technology and activated alumina work because they are able to sequester arsenic by attaching themselves to, or adsorbing, the toxic metal. Such adsorbent technologies are sensitive to the pH of water, and the amount of arsenic they can adsorb decreases as the pH goes up. Therefore, the fact that the Idaho groundwater used in the tests had a pH higher than 7 and contained silica is significant, says Patrick Brady, a senior scientist at Sandia National Laboratories, which is also developing arsenic removal technologies. But he is waiting for the field tests that Tranter says he hopes to conduct “soon.”
A few other companies have also made resins that remove arsenic by capitalizing on its affinity for iron oxide. But INL’s new material surpasses the others on more than one count, Tranter says.
“We have created nanoparticles [that] have a lot higher surface area . . . increased by a factor of 3–4 over current technologies,” Tranter explains. That means more reactant sites for arsenic to adsorb on the iron oxide. The material also contains much more adsorbent—85% iron oxide by mass, compared with 20–40% for competing technologies. In Tranter’s lab tests, 10–12 milligrams of arsenic were sorbed on each gram of resin.
This is a fairly high adsorbing capacity, says Paul Westerhoff, a civil and environmental engineering professor at Arizona State University, who calls the INL technology “promising.”
The spent adsorbent passes the U.S. EPA’s Toxicity Characteristic Leaching Procedure test; this means it is not a hazardous waste and can be safely disposed. “There are no safety or ecological concerns associated with the resin,” Tranter says.
The resin should be cheap to make because the raw material is inexpensive, he adds. The INL estimates that using it will cost utilities about 10 cents per thousand gallons of water. Plus, operating costs will be lower compared with other adsorbents. “We can treat 2–3 times as much water [per gallon], which puts long-term cost down by a factor of two,” Tranter says.
The higher cost of water resulting from the use of arsenic treatment technologies that meet the EPA standard is an “acute” problem in rural communities, Brady says. People in these communities who cannot afford to pay more for water could start depending on private water sources, which are unregulated. For rural areas, he says, the technology’s cost plays an enormous role.
