Non-toxic catalyst for clean, reusable water

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

As wastewater treatment for reuse as drinking water becomes a viable and popular way to address water scarcity, what are the harmful by-products of treatment and how to eliminate them. One group of these chemicals, aldehydes, is known to be stubborn during processing. Aldehydes that are toxic to humans will be at the top of the list of regulated by-products in forthcoming reuse regulations, USC researchers say, and require the removal of sustainable methods from our drinking water.

In one in a business diary Environmental science and technology In a published study, researchers at the USC Viterbi School of Engineering use platinum to remove even the most resistant toxins from wastewater. Platinum, the same metal used in catalysts to clean airborne pollutants in car exhaust, can act as a catalyst, accelerating oxidation and converting once-toxic aldehydes to harmless carboxylic acids, according to Dan McCurry, an assistant professor of civil and environmental engineering. .

When wastewater is recycled, McCurry says, the resulting water is “very pure, but not 100 percent pure. A small amount of organic carbon is still detectable, and these carbon atoms can be attached to molecules that are very toxic or completely harmless.” It has confused people for years, he said, mainly because carbon is able to go through many layers of treatments and barriers.

According to McCurry, a study by UC Berkeley researcher David Sedlak found that “one-third to half” of these molecules are in the form of aldehydes. 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, which means that 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-receiving oxidizing agents or photochemistry has not yet been demonstrated in a sustainable manner. Until now.

Solving the upcoming problem

McCurry recalled learning about oxidizing agents for molecule synthesis in an organic chemistry class while studying at Stanford University. “The lecturer was going through a list of oxidants used by synthetic chemists, and I was fascinated by platinum catalysts. Not only is it one of the few oxidants that is nontoxic, but it can also use oxygen in water to create a … Catalyze the reaction abiotically (without the use of 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 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, says McCurry, the reaction is slow. With platinum, the process speeds up. McCurry and his research team have been using platinum to oxidize the various drugs they have been experimenting with for some time.

“We knew we could oxidize certain things, but we didn’t have a clear application for this catalyst,” says McCurry. In the end, they hoped to find effective employment for their work. After a year of experimentation, 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 oxygen is already present in the water, it would be closest to oxidation without chemicals.

McCurry acknowledges that platinum is expensive, but also points out that, as with a car catalytic converter, costs are relative. “Your car probably contains between one and 10 grams of platinum. The amount is not trivial. If it’s cheap enough to use a Honda Civic, it would probably be cheap enough to use a water treatment system,” McCurry said.

The breakthrough, says McCurry, is less relevant to most existing water reuse facilities because many prefer “indirect drinking water reuse.” This involves pumping water back into the ground after all water treatment and recycling processes have been completed, which essentially creates new groundwater. “Once the aldehydes are in the soil, they are likely to be eaten by a microbe and the water cleared,” he said.

“This is a closed water loop, with the water being led from the treatment plant to the reuse facility and then either to the drinking water treatment plant or directly to the distribution systems of households and companies.

In these cases, aldehydes could potentially reach consumers, McCurry said. Although not currently regulated, McCurry suspects that 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 now we know that this catalyst, which we used to oxidize random drugs, also works great in oxidizing aldehydes – and that it would allow it.” direct re-use because drinking water meets future regulatory guidelines and safety standards, ”he said.

The team conducted the first platinum experiment in batch reactors with several liters of water. The experiments were successful, but McCurry says mass production will require further research to determine how long the catalyst will remain active. The team is also researching how the catalyst can potentially be regenerated. McCurry says it’s also important to test the system with dirtier water because it can clog the catalyst and reduce its efficiency.

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

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