For decades, water utilities have relied on giant tanks filled with ion-exchange resin beads to remove perchlorate, a harmful industrial pollutant, from drinking water.
The system works by attracting negatively charged perchlorate ions to positively charged resin beads, allowing purified water to flow out of the tanks. But the process leaves behind a difficult problem: resin beads loaded with perchlorate that must be regenerated or disposed of as hazardous waste.
Now, researchers at UC Riverside have developed a catalyst made from tiny ruthenium nanoparticles that effectively breaks down perchlorate at high concentrations.
The breakthrough study, published in the journal “ACS Central Science,” could make it possible to destroy perchlorate after it has been captured on ion-exchange resin, potentially reducing the hazardous waste generated during drinking water treatment, allowing for the resin beads to be reused, said Jinyong Liu, UCR associate professor of chemical and environmental engineering, who oversaw the research that was led by UCR post doctoral research scientist Jinyu Gao.
The advance comes as the U.S. Environmental Protection Agency moves toward establishing the first national drinking water standard for perchlorate as California did nearly two decades ago.
Perchlorate is a chemical used in rocket propellants, explosives, fireworks, and other energetic materials. It also occurs naturally in some environments. The compound has contaminated groundwater below military installations, defense manufacturing sites, and other industrial locations throughout the United States.
If ingested, perchlorate interferes with the thyroid gland’s ability to absorb iodine, disrupting the production of hormones that regulate growth, metabolism, and brain development. Infants, young children, and pregnant women are considered especially vulnerable.
California has regulated perchlorate in drinking water for years, and set a maximum contamination level, or MCL, at no more than 6 parts per billion. Meanwhile, the EPA recently resumed efforts to establish a national drinking water standard, a move expected to increase demand for treatment technologies.
Liu said current treatment systems remove perchlorate effectively but do not destroy it.
Previous catalysts developed by Liu’s laboratory could destroy perchlorate in either acidic or alkaline conditions. The new catalyst is the first the group has developed that works rapidly at a neutral pH at room temperature, the condition found in most drinking water treatment systems.
“This gives us a complete toolbox,” Liu said. “We now have catalyst systems that work under acidic, alkaline, and neutral conditions, allowing us to address a much wider range of real-world water treatment applications.”
The catalyst uses nanoparticles of the metal ruthenium enhanced with an organic nitrogen-containing compound known as cis-DACH. Together they rapidly convert perchlorate into harmless chloride, the same ion found naturally in table salt, at room temperature and under normal atmospheric pressure.
Unlike earlier catalyst systems, the new one also remains effective in water containing nitrate, another common groundwater contaminant. Previous catalysts could be deactivated by nitrate, often requiring separate treatment steps. The new catalyst removes nitrate first and then continues breaking down perchlorate, simplifying the cleanup process.
The researchers say the technology could prove especially valuable for treating the concentrated waste streams produced when ion-exchange resins are regenerated, as well as highly contaminated industrial wastewater from defense manufacturing, explosives disposal and other facilities where perchlorate concentrations are much higher than those found in drinking water.
Liu said the catalyst could eventually complement existing water treatment systems rather than replace them.
“Ion exchange is still the fastest way to remove perchlorate from drinking water,” he said. “Our goal is to provide a much better way to destroy the concentrated perchlorate after it has been captured.”
Disposing of or regenerating the resin has become more complicated because the beads now often contain not only perchlorate but also per- and polyfluoroalkyl substances, or PFAS, a class of persistent industrial chemicals known as “forever chemicals.” Liu’s laboratory has also developed technologies to destroy PFAS. He said the new ruthenium catalyst complements that work by destroying perchlorate, another persistent contaminant that is often removed from drinking water using the same treatment systems.
The title of the study is “Catalytic Reduction of Aqueous Perchlorate at Neutral pH." In addition to Liu and Gao, the co-authors, are Shaohua Xie, Jianjun Chen, Qingsong Luo, Juchen Guo, Yadong Yin, and Fudong Liu. Jinyong Liu is the corresponding author. All are with UCR.
