A non-toxic catalyst for clean, reusable water

Platinum has set a new “gold standard” in jewelry and is now also meant to improve the quality of your water.

As treating wastewater for reuse as drinking water becomes a viable and popular option for addressing water shortages, what are the harmful by-products of treatment and how to eliminate them. One group of these chemicals, aldehydes, are known to be stubborn in processing. Aldehydes, which are toxic to humans, will top the list of regulated byproducts in upcoming reuse regulations, USC researchers say, and require sustainable methods to be removed from our drinking water.

In one in the trade newspaper Environmental sciences and technologies In the published study, researchers at the USC Viterbi School of Engineering use platinum to remove even the most stubborn toxins from wastewater. Platinum, the same metal used in catalytic converters to clean air pollutants in car exhausts, can act as a catalyst, according to Dan McCurry, assistant professor of civil and environmental engineering, and accelerate oxidation to convert once toxic aldehydes into harmless carboxylic acids.

When wastewater is recycled, McCurry says, the resulting water is “very pure, but not 100% pure. A small amount of organic carbon is still detectable, and those carbon atoms can be attached to very toxic or completely harmless molecules.” “. This has baffled people for years, he said, especially since carbon is able to overcome so many layers of treatment and barriers.

A study by UC Berkeley researcher David Sedlak found that “one third to half” of these molecules are in the form of aldehydes, according to McCurry. Aldehydes are chemical compounds characterized by a carbon atom that has a double bond with an oxygen atom, a single bond with a hydrogen atom, and a single bond with another atom or group of atoms. They are also typically toxic to humans, meaning their long-term consumption can lead to a number of chronic and life-threatening diseases, including cancer.

According to McCurry, the catalytic oxidation of organic pollutants in water without electrochemistry, the addition of electron-accepting oxidizing agents or photochemistry has not yet been sustainably demonstrated. Until now.

A solution to an impending problem

McCurry recalled learning about oxidizing agents for the synthesis of molecules in an organic chemistry course he took while attending Stanford University. “The teacher was examining a list of oxidants used by synthetic chemists and the platinum catalysts caught my attention. Not only is it one of the few non-toxic oxidants, but it can also use the oxygen in water to create a … Catalyze the reaction abiotically (without using microbes).

“I found it really exciting,” McCurry said, “because one of the frustrations of water treatment has always been that the water is full of oxygen which doesn’t actually do anything.”

According to McCurry, water contains about eight milligrams of dissolved oxygen per liter. From a thermodynamic point of view, although oxygen is a strong oxidizing agent, McCurry says, the reaction is slow. With platinum, the process speeds up. For a while, McCurry and his research team have been using platinum to oxidize various drugs to experiment with.

“We knew we could oxidize some things, but we didn’t have a clear application for this catalyst in mind,” says McCurry. Eventually, they hoped to find an effective application for their work. After a year of experimenting, he finally got the idea as he cycled home from the Stanford campus. “What if we could use platinum in water treatment to oxidize contaminants,” he said. “Since oxygen is already present in the water, this would be the closest thing to chemical-free oxidation.

McCurry acknowledges that platinum is expensive but also points out that, like a car’s catalytic converter, the cost is relative. “Your car probably contains between one and 10 grams of platinum. The amount isn’t trivial. If it’s cheap enough to fit a Honda Civic, it’s probably cheap enough to fit a water treatment system,” McCurry said.

The breakthrough, McCurry says, isn’t that relevant to most existing water reuse plants, as many of them prefer “indirect drinking water reuse.” This involves pumping water into the ground after all water treatment and recycling processes have been completed, essentially creating new groundwater. “Once the aldehydes are in the soil, they are likely to be eaten by a microbe and the water is purified that way,” he said.

“It is a closed water circuit, with the water being conveyed from the treatment plant to the reuse plant and then to a drinking water treatment plant or directly into the domestic and corporate distribution system.

In such cases, the aldehydes could potentially reach consumers, McCurry said. Although currently unregulated, McCurry suspects the presence of aldehydes in reused wastewater will soon attract the attention of authorities. “We didn’t know we had a solution to this problem, but we now know that this catalyst, which we used to oxidize adventitious pharmaceuticals, also works brilliantly in the oxidation of aldehydes and would allow it.” direct reuse of drinking water meets future regulatory guidelines and safety standards, “he said.

The team conducted a first experiment with platinum in batch reactors with just a few liters of water. The experiments were successful, but McCurry says mass production will require further research to determine how long the catalyst remains active. The team is also studying how the catalyst can potentially be regenerated. McCurry says it’s also important to test the system with dirtier water, as this can clog the catalyst and make it less effective.

The process, for which the team has applied for a patent, is said to be more sustainable than alternative methods that may require the use of additional chemicals and energy, McCurry said.

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