28 July 2009

Atom substitution brings cleaner water

Just by simply substituting a single atom in a molecule widely used to purify water, there is now an effective decontaminant with a shelf life superior to products currently on the market.

The material can remove 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, said researchers from Sandia National Laboratories.

“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 water-treatment reagent, known as a coagulant, comes from substituting an atom of gallium in the center of an aluminum oxide cluster, itself a commonly used coagulant in water purification, Nyman said.

The substitution is not 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,” Nyman said. “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,” Nyman said.

For related information, go to www.isa.org/manufacturing_automation.