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A non-toxic catalyst for clean, re-usable water

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Platinum has set a new “gold standard” in jewelry and now it’s about to improve the quality of your water.

As wastewater treatment for drinking water reuse becomes a more viable and popular option to address water shortages, the question arises as to what harmful by-products can form during treatment and how to address them. A group of these chemicals, aldehydes, are known to persist during treatment. Toxic to humans, aldehydes will top the list of regulated byproducts in future recycling regulations, USC researchers believe, requiring a sustainable method to be removed from our drinking water.

In research published in Environmental Science and Technology, researchers at the USC Viterbi School of Engineering are introducing platinum to remove even the most stubborn toxins from wastewater. Platinum, the same metal used in catalytic converters to clean up air pollutants in car exhaust, could act as a catalyst, said Dan McCurry, assistant professor of civil and environmental engineering, speeding up oxidation to convert 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 small amount of organic carbon detectable, and these carbon atoms can be attached to molecules that are highly toxic or completely harmless.” This has baffled people for years, he said, mainly because the carbon is able to get through so many layers of treatment and barriers.

A study conducted by UC Berkeley researcher David Sedlak revealed that “a third to a halfSome of these molecules are present in the form of 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 single bond with another atom or. are also generally toxic to humans, meaning that long-term use can lead to a variety of chronic and life-threatening diseases such as cancer.

Catalytic oxidation of organic pollutants in water, without electrochemistry, addition of electron-accepting oxidizers or photochemistry, has not been demonstrated sustainably so far, McCurry said. Until now.

A solution for an upcoming problem

McCurry recalled learning about oxidizers used to synthesize molecules in an organic chemistry course he took when he was a graduate student at Stanford University. “The TA went through a list of oxidants used by synthetic chemists and platinum catalysts caught my attention. Not only is it one of the few oxidants that is non-toxic, but it can use the oxygen in water to initiate a reaction abiotically.” to catalyze (without the use of microbes).”

“It was really exciting for me,” McCurry said, “because in water treatment it’s always been frustrating that water is full of oxygen, but it actually doesn’t do anything.”

There are about eight milligrams per liter of dissolved oxygen in water, McCurry said. While it’s a potent oxidizer from a thermodynamic perspective, McCurry said, the reaction is slow. Platinum speeds up the process. For a time, McCurry and his team of researchers used platinum to oxidize various drugs as a matter of experimentation.

“We knew we could oxidize certain things, but we didn’t have a clear application in mind for this catalyst,” McCurry said. Ultimately, they hoped to find an impactful application for their work. Finally, after a year of experimentation, the idea occurred to him while riding his bike 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 because the oxygen is already in the water, it’s the closest thing to a chemical-free oxidation.”

McCurry acknowledges that platinum is expensive, but also notes that the cost, such as for a car’s catalytic converter, is relative. “Your car probably contains between one and 10 grams of platinum. The amount is not trivial. If it’s cheap enough to put in a Honda Civic, it’s probably cheap enough to put in a water treatment plant,” McCurry said.

The breakthrough, McCurry said, isn’t as relevant to most existing water reuse plants, as many of them prefer “indirect potable reuse.” This is where, after all the water treatment and recycling processes are complete, the water is pumped back into the ground – so they essentially create 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 drinking water reuse,” he said, “where we are talking about a closed water cycle where water goes from the wastewater treatment plant to the reuse plant and then either to a drinking water plant or directly to the distribution system in homes and businesses. .”

In these cases, aldehydes may be able to reach consumers, McCurry said. While not currently regulated, McCurry suspects that the presence of aldehydes in recycled wastewater will soon attract regulatory attention. “This is the problem that we didn’t realize we had a solution to, but now we know that this catalyst, which we’d used for fun to oxidize random drugs, does a great job of oxidizing aldehydes — and it’s water could be reused directly potable to meet future regulatory guidelines and safety standards,” he said.

The team conducted a preliminary experiment with platinum in batch reactors on a few liters of water. The experiments were successful, but McCurry says that in order to catch on at the mass production level, additional research needs to be done on how long the catalyst stays active. The team is also investigating how the catalyst could potentially be regenerated. McCurry says it will also be important to test the system with dirtier water, which can contaminate the catalytic converter and make it less effective.

The process, for which the team has applied for a patent, will appear more sustainable than alternative methods that may require additional chemicals and energy, McCurry said.


Researchers identify the molecule responsible for a potent carcinogen found in recycled wastewater


More information:
Euna Kim et al, Out of the blue? Catalytic oxidation of trace aqueous aldehydes with dissolved oxygen in the environment, Environmental Science and Technology (2022). DOI: 10.1021/acs.est.2c00192

Provided by the University of Southern California


Quote: Towards Platinum: A Non-Toxic Catalyst for Clean, Reusable Water (2022, June 15) Retrieved June 15, 2022 from https://phys.org/news/2022-06-platinum-non-toxic-catalyst- re -usable.html

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