A non-toxic catalyst for clean, reusable water

Platinum has set a new “gold standard” in jewelry, and now it’s meant to enhance the quality of your water too.

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

In one in the trade journal Environmental Science & Technology In the study published, 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 airborne pollutants in car exhaust, can act as a catalyst, according to Dan McCurry, assistant professor of civil and environmental engineering, and speed up 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 percent pure. A tiny amount of organic carbon is still detectable, and those carbon atoms can be attached to molecules that are very toxic or completely harmless .” This has baffled people for years, he said, largely because the carbon is able to get through so many layers of treatment and barriers.

A study by UC Berkeley researcher David Sedlak found that “one-third to one-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 demonstrated in a sustainable manner. Until now.

A solution to an upcoming problem

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

“I found that really exciting,” McCurry said, “because one of the frustrations of water treatment has always been that water is full of oxygen that doesn’t really 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 used platinum to oxidize various drugs to experiment with.

“We knew we could oxidize certain things, but we didn’t have a clear application in mind for this catalyst,” McCurry says. Ultimately, they hoped to find an effective application for their work. After a year of experimenting, he finally got the idea while riding his bike home from the Stanford campus. “What if we could use platinum in water treatment to oxidize contaminants,” he said. “Since the 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 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 system,” McCurry said.

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

“This is a closed water loop, with the water being routed from the treatment plant to the reuse plant and then either to a drinking water treatment plant or directly into the household and business distribution system.

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

The team conducted a first experiment with platinum in batch reactors with a few liters of water. The experiments were successful, but McCurry says mass production will require more research to determine how long the catalyst stays active. The team is also investigating how the catalyst can potentially be regenerated. McCurry says it’s also important to test the system with dirtier water, as this can foul 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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