Detoxifier. A new "green" catalyst breaks down into its constituent elements: carbon, nitrogen, oxygen, and iron.

A New Weapon for Cleaning Wastewater

Wastewater cleanup crews may soon have a safer, more efficient way to destroy toxic, humanmade pollutants known as nitrophenols. Researchers have developed a "green" nitrophenol degrader that disintegrates when its work is complete and that appears harmless to animals and plants in early toxicity studies.

Manufacturers use nitrophenols to produce dyes, fungicides, and pharmaceuticals, among other products. Discharged in wastewater streams, the chemicals do not degrade easily and are toxic to aquatic life. Until now, the most common way to break down nitrophenols in wastewater was to use a mixture of hydrogen peroxide and iron salts. But this process only works in acidic environments and often leaves behind an iron sludge that requires a secondary cleanup to keep it from affecting the environment.

In contrast, the chemical solution developed by chemist Terry Collins and doctoral student Arani Chanda at Carnegie Mellon University in Pittsburgh, Pennsylvania, works at most natural pH levels and uses a fraction of the iron. The solution is a member of the Fe-TAML (or iron tetra-amido macrocyclic ligand) group of catalysts, which work with hydrogen peroxide to break the bonds of some pesticides, dyes, and other chemicals, thus destroying them. Unlike the Fenton process, Fe-TAMLs don't require a secondary cleanup. Once their work is done, the catalysts themselves break down into elements commonly found in nature, such as carbon, nitrogen, and oxygen--hence their "green" quality. The findings--presented yesterday at a meeting of the American Chemical Society (ACS) in Washington, D.C.--mark the first time researchers have successfully used Fe-TAMLs to degrade nitrophenols.

Paul Anastas, director of ACS's Green Chemistry Institute, says he welcomes the latest development. He calls Collins's work on Fe-TAMLs is "absolutely brilliant" and "cutting edge." In addition to wastewater cleanup, Collins believes Fe-TAMLs can be used to reduce the environmental impact of paper bleaching and might make common detergents more efficient. "It has the potential to dramatically impact our daily lives," he says.

Related sites
Carnegie Mellon Institute for Green Oxidation Chemistry
American Chemical Society Green Chemistry Institute
U.S. Environmental Protection Agency Green Chemistry site