Platinum has set a new “gold standard” in jewelry, and now it’s poised to improve your water quality.
As treating wastewater for reuse as drinking water becomes a more viable and popular option for dealing with water shortages, the question arises as to what harmful by-products might form during treatment and how to address them. importantly. One group of these chemicals, the aldehydes, are known to persist stubbornly during processing. Toxic to humans, aldehydes will be high on the list of regulated byproducts in upcoming reuse regulations, USC researchers believe, and require a sustainable methodology to be removed from our drinking water.
In research published in Environmental science and technology, USC Viterbi School of Engineering researchers are introducing platinum to help clean even the most stubborn toxins from wastewater. Platinum, the same metal used in catalytic converters to clean air pollutants from car exhaust, can act as a catalyst, said Dan McCurry, assistant professor of civil and environmental engineering, accelerating oxidation to transform once toxic aldehydes into harmless carboxylic acids.
When wastewater is recycled, McCurry said, the resulting water is “very pure, but not 100 percent pure.” There is still a tiny amount of detectable organic carbon, and those carbon atoms could be attached to very toxic or completely innocent molecules. This has puzzled people for years, he said, particularly because carbon is able to pass through so many layers of processing and barriers.
A study conducted by UC Berkeley researcher David Sedlak found that “a third to a half“Of these molecules are present as aldehydes, McCurry said. Aldehydes are chemical compounds characterized by a carbon atom that shares a double bond with an oxygen atom, a single bond with a hydrogen atom, and a simple bond with another atom or group of atoms.They are also generally toxic to humans, which means that their long-term consumption could lead to various chronic and life-threatening diseases such as cancer.
Catalytic oxidation of organic pollutants in water, without electrochemistry, the addition of oxidizing electron-accepting chemicals, or photochemistry, has not been demonstrated sustainably to date, McCurry said. So far.
A solution for a future problem
McCurry remembers learning about oxidants used to synthesize molecules in an organic chemistry class he took as a graduate student at Stanford University. “The TA was browsing through a list of oxidants used by synthetic chemists and the platinum catalysts caught my eye. Not only is it one of the few non-toxic oxidants, but it can use the oxygen in water to catalyze a reaction abiotically (without the use of microbes).
“That was really exciting to me,” McCurry said, “because it’s always been frustrating in water treatment for the water to be full of oxygen, but it really doesn’t matter.”
There are about eight milligrams per liter of dissolved oxygen in water, McCurry said. Although it’s a strong oxidant from a thermodynamic perspective, McCurry said, the reaction is slow. With platinum, the process accelerates. For a time, McCurry and his team of researchers used platinum to oxidize different pharmaceuticals on an experimental basis.
“We knew we could oxidize some things, but we didn’t have a clear application in mind for this catalyst,” McCurry said. Ultimately, their hope was to find an impactful application for their work. Eventually, after a year of experimentation, the idea came to him as he was cycling home from the Stanford campus. “What if we could use platinum in water treatment to oxidize contaminants?” he said. “It would essentially happen for free, and since the oxygen is already in the water, that’s the closest thing to chemical-free oxidation.”
McCurry acknowledges that platinum is expensive, but also notes that cost, like a car’s catalytic converter, is relative. “Your car probably contains between 1 and 10 grams of platinum. The amount is not negligible. If it’s cheap enough to install a Honda Civic, it’s probably cheap enough to install a water treatment plant,” McCurry said.
The breakthrough, McCurry said, isn’t as relevant to most existing water reuse plants because many of them promote “indirect drinking water reuse.” This is where, after all the water treatment and recycling processes are complete, the water is returned to the ground, essentially creating new groundwater. “Once they’re in the ground, it’s likely that a microbe will eat the aldehydes and the water will be cleaned that way,” he said.
“But more and more people are talking about direct potable reuse,” he said, “where we’re talking about a closed water loop where the water goes from the treatment plant to the reuse and then either to a drinking water plant or directly into the distribution system in homes and businesses.
In those cases, aldehydes could potentially reach consumers, McCurry said. Although currently unregulated, McCurry suspects that the presence of aldehydes in recycled wastewater will soon attract the attention of regulatory authorities. “This is the problem we didn’t know we had a solution for, but now we know that this catalyst, which we used to oxidize random pharmaceuticals for fun, works great on oxidizing aldehydes and would allow direct reuse of drinking water to meet future regulatory guidelines and safety standards,” he said.
The team did a preliminary experiment using platinum in batch reactors on a few gallons of water. The experiments were successful, but McCurry says that for this to spread to a mass production level, more research would need to be done on how long the catalyst remains active. The team is also investigating how to potentially regenerate the catalyst. McCurry says it will also be important to test the system with dirtier water, which can clog the catalyst and make it less efficient.
The process, for which the team has a patent pending, will appear more sustainable than alternative methods that may require the introduction of additional chemicals and energy, McCurry said.
Researchers identify the molecule responsible for a powerful carcinogen found in recycled wastewater
Euna Kim et al, Out of Thin Air? Catalytic oxidation of trace aqueous aldehydes with ambient dissolved oxygen, Environmental science and technology (2022). DOI: 10.1021/acs.est.2c00192
Go platinum: a non-toxic catalyst for clean, reusable water (June 15, 2022)
retrieved June 15, 2022
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