Can GAC Be Used to Control Priority Unregulated DBPs in Drinking Water?

Thought LeadersProf. Susan RichardsonArthur Sease Williams Professor of Chemistry
Department of Chemistry and Biochemistry
University of South Carolina

An interview with Professor Susan Richardson, conducted by Stuart Milne, BA

Your presentation at Pittcon focussed on GAC for controlling priority unregulated disinfection by-products (DBPs) in drinking water. What are the current challenges associated with unregulated DBPs in drinking water?

The US EPA currently regulates only 11 disinfection by-products, DBPs, in drinking water, but we have identified, more than 700. Many scientists, myself included, believe that the human health effects that we see in epidemiologic studies, may be related to some of the more toxic, unregulated DBPs that are not controlled currently through drinking water regulations.

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Why has granular activated carbon (GAC) received renewed interest compared to other methods?

We have known about GAC for around 30 years, and there has been a lot of promising research on it, but despite this, in many cases it has not been put in place as many people think that it would be too expensive to switch to GAC. Instead, a number of drinking water treatment plants have switched disinfectants, for example from using chlorine to chloramine, to lower the levels of regulated DBPs. By switching disinfectants in this way, plants that previously struggled to meet regulations can become compliant.  

However, we have noticed that potentially hazardous DBPs can occur as a result of the switch, including NDMA, nitrosodimethylamine, a very potent carcinogen. So now, the U.S. EPA and the research community are thinking of how to reach a suitable solution by going back to square one and asking the initial question – are there ways we can remove the precursor material better to prevent DBP formation, and ultimately lower the level of DBPs?

There has been some indication that brominated species may increase in formation when using GAC. What research have you done to investigate the ability of GAC to remove unregulated DBPs?

Earlier studies indicated that two regulated brominated trihalomethanes increased with the use of GAC. However, no research had been done beyond that to look at other brominated DBPs, ones that are more toxic than regulated DBPs.

That's where we came in - we took about 60 unregulated priority DBPs, developed analytical methods for them, measured them with and without GAC, and with different types of GAC. We also experimented with different disinfectants, with and without prechlorination, and even using chloramination.

We’re investigating, for the first time, a really broad sweep of DBPs, including the really toxic brominated ones, to understand if GAC will work for them.

What analytical techniques have you used to investigate these DBPs?

We use gas chromatography with mass spectrometry, GC-MS, and also GC-MS/MS, tandem mass spectrometry. Another tool that we use is a total organic halogen (TOX) analyzer. With the TOX analyzer, we can measure not only the DBPs that we know are in the drinking water, but it also accounts for the chlorinated, brominated, and iodinated material that we don’t about and can’t measure yet.

In general, the brominated and iodinated DBPs are much more toxic than the chlorinated ones, so the total organic halogen analysis gives us an idea of what's there (beyond the things we can measure). And, with the 60 DBPs that we are quantifying, we're able to get a very comprehensive measurement of the DBPs.

Ultimately, our aim is to make drinking water safer, and so we want to find out if GAC can do this.

Granular Activated Carbon for Water Treatment from AZoNetwork on Vimeo.

What impact does the age of GAC and types of GAC have on filtering DBPs in drinking water?

The aging of GAC is much like how we expect the material in our home water filters to age – after a while, you need to change it.  GAC at a drinking water treatment plant is like having a huge Brita filter.

Sites within the filter get filled up with material as it sorbs and removes unwanted materials from your water, to the point where they stop removing DBP precursors as effectively - then it's time to regenerate that GAC.

Does GAC offer a long-term solution for reducing levels of unregulated DBPs in drinking water?

I would say so, especially as we saw such good results with it. Some of the plants we looked at were reducing the DBP levels by as much as 80% with a young GAC filter.

It is worth noting that in some cases however, we did see an increase in some brominated DBPs that were toxic, just like the early work that saw two of the brominated trihalomethanes increase. But overall, when we looked at it across the board, it's still a beneficial route to take in producing safer water.

What are the next steps in your research?

Although we were able to measure the DBPs and the total organic halogen under all kinds of scenarios in our research, we were limited by our funding in that we were not able to get real toxicology testing – instead, we calculated the in vitro cytotoxicity using the measured DBPs that we have, and using the cytotoxicity potencies that we know of from other studies.

Therefore, our next steps are to have real toxicity involved in our work, combining the chemistry and comprehensive toxicology.

What did you gain from attending Pittcon 2018 and discussing your research?

I love sharing my research with others, it’s good to inform others on the work we are doing.

If I’m able to educate people with my talk at Pittcon, that GAC is a good way to go, then maybe others will promote that in their utilities and share their new knowledge with people they know in the field.

I also attend Pittcon to learn, too. I learned about new analytical techniques, new developments, new findings. It's always exciting to come to conferences and learn new things. That's a big part of it!

About Prof. Susan Richardson

Susan D. Richardson is the Arthur Sease Williams Professor of Chemistry in the Department of Chemistry and Biochemistry at the University of South Carolina.  Prior to coming to USC in January 2014, she was a Research Chemist for several years at the U.S. EPA’s National Exposure Research Laboratory in Athens, GA.  For the last several years, Susan has been conducting research in drinking water—specifically in the study of toxicologically important disinfection by-products (DBPs).

Susan is the recipient of the 2008 American Chemical Society Award for Creative Advancements in Environmental Science & Technology, has received an honorary doctorate from Cape Breton University in Canada (2006), was recently recognized as an ACS Fellow (2016), and was recently elected Vice President / President Elect of the American Society for Mass Spectrometry (2018).

She also serves as an Associate Editor of Environmental Science & Technology and for Water Research and is on the Editorial Advisory Board of Rapid Communications in Mass Spectrometry, Journal of Hazardous Materials, Environmental Science and Pollution Research, and Journal of Environmental Sciences.  Susan has published more than 140 journal articles and book chapters and has written many invited biennial reviews for the journal Analytical Chemistry—on Emerging Contaminants in Water Analysis and Environmental Mass Spectrometry, She has a Ph.D. in Chemistry from Emory University and a B.S. in Chemistry & Mathematics from Georgia College & State University.

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