To Catch a Carcinogen

As populations around the world face water scarcity, water reuse has gained recognition as a valuable resource. While today’s advanced filtration methods and water recycling technologies are highly sophisticated and continue to make tremendous progress, there remain a number of challenges to address with direct potable reuse.

One such challenge is the elimination of disinfection byproducts that are harmful to humans such as N-Nitrosodimethylamine, also known as NDMA. NDMA is a potent carcinogen that forms as an unintended product of the chlorination process. And it’s a substance that is not only detrimental to humans, it’s difficult to eliminate through traditional water treatment processes.

Indirect potable reuse systems process wastewater and pump it into the ground, where the soil can help remove chemicals and harmful compounds before it goes on to the drinking water plant. However this process is more expensive than direct potable reuse in which water is purified and made immediately available for human consumption.

In the 1990s, when high concentrations of NDMA were found in clean recycled wastewater, researchers identified monochloramine, a component of the chlorine mixture, as the molecular culprit since it is known to react with dichloramine and cause the formation of NDMA. Plant operators began changing chlorine chemistries in order to lower dichloramine concentrations and effectively reduce NDMA formation.

But subsequent studies found that other chemicals such as pharmaceutical antacids form NDMA when chlorinated, leaving researchers wondering if monochloramine was really to blame.

Through extensive research, USC Viterbi Assistant Professor Daniel McCurry, assisted by Meredith Huang and Shiyang Huang, determined recently that the chemical responsible for the formation of NDMA, in recycled wastewater is actually dichloramine. Their study, which demonstrated significantly higher NDMA yields from dichloramination than from monochloramination, is published in Environmental Science and Technology Letters.

“Our paper showed that dichloramine is responsible for the formation of NDMA from these pharmaceutical-derived precursors. And we were able to see that you get more and more NDMA as you increase monochloramine, but that’s just because of monochloramine going to dichloramine,” McCurry told Ashleen Knutson, reporting for USC’s Viterbi School of Engineering. “So, our results from fundamental chemistry work support the practical observation that minimizing dichloramine minimizes NDMA formation.”