By substituting a single atom in a molecule widely used to purify water, researchers
at Sandia National Laboratories
have created a far more effective decontaminant with a shelf life superior to
products currently on the market.
This bar graph shows the efficacy of removing wild-type bacteriophage from Rio Grande water using the all-aluminum coagulant (yellow), the gallium-aluminum coagulant (pink) and a germanium-aluminum coagulant (green). While the gallium-aluminum coagulant is most effective, the germanium-aluminum coagulant is less effective than the all-aluminum coagulant. The gallium makes the active ingredient for binding contaminants more stable and effective, while the germanium, introduced as another variable, was found to make the active ingredient less stable and less effective. Credit: Mona Aragon, Sandia National Laboratories
Sandia has applied for a patent on the material, which removes bacterial, viral
and other organic and inorganic contaminants from river water destined for human
consumption, and from wastewater treatment plants prior to returning water to
the environment.
"Human consumption of 'challenged' water is increasing worldwide as preferred
supplies become more scarce," said Sandia principal investigator May Nyman.
"Technological advances like this may help solve problems faced by water
treatment facilities in both developed and developing countries."
The study was published in June 2009 in the journal Environmental Science &
Technology (a publication of the American Chemical Society) and highlighted
in the June 22 edition of Chemical & Engineering News. Sandia is working
with a major producer of water treatment chemicals to explore the commercial
potential of the compound.
The water-treatment reagent, known as a coagulant, is made by substituting
an atom of gallium in the center of an aluminum oxide cluster — itself
a commonly used coagulant in water purification, says Nyman.
The substitution isn't performed atom by atom using nanoscopic tweezers but
rather uses a simple chemical process of dissolving aluminum salts in water,
gallium salts into a sodium hydroxide solution and then slowly adding the sodium
hydroxide solution to the aluminum solution while heating.
"The substitution of a single gallium atom in that compound makes a big
difference," said Nyman. "It greatly improves the stability and effectiveness
of the reagent. We've done side-by-side tests with a variety of commercially
available products. For almost every case, ours performs best under a wide range
of conditions."
Wide-ranging conditions are inevitable, she said, when dealing with a natural
water source such as a river. "You get seasonal and even daily fluctuations
in pH, temperature, turbidity and water chemistry. And a river in central New
Mexico has very different conditions than say, a river in Ohio."
The Sandia coagulant attracts and binds contaminants so well because it maintains
its electrostatic charge more reliably than conventional coagulants made without
gallium, itself a harmless addition.
The new material also resists converting to larger, less-reactive aggregates
before it is used. This means it maintains a longer shelf life, avoiding the
problem faced by related commercially available products that aggregate over
time.
"The chemical substitution [of a gallium atom for an aluminum atom] has
been studied by Sandia's collaborators at the University of California at Davis,
but nobody has ever put this knowledge to use in an application such as removing
water contaminants like microorganisms," said Nyman.
The project was conceived and all water treatment studies were performed at
Sandia, said Nyman, who worked with Sandia microbiologist Tom Stewart. Transmission
electron microscope images of bacteriophages binding to the altered material
were achieved at the University of New Mexico. Mass spectroscopy of the alumina
clusters in solution was performed at UC Davis.