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Water Today Title April 14, 2024

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2022/3/7 Contaminants - PSAS

brought to you in part by

Noah Trekker

Inventing solutions for the most pressing modern problems: Removing toxic PFAS from water

Frank Leibfarth, Ph.D. Chemist From UNC Chapel Hill

WT staff

WT: I have with me, Frank Leibfarth, Assistant Professor of Chemistry at University of North Carolina, Chapel Hill; Popular Science rates him as top ten up and coming minds in science. Thanks for doing this, can you tell me what you and your team have invented, and why you wanted to invent this?

Leibfarth: Sure, thanks. We have developed a granular resin technology, which allows us to remove PFAS (perfluorinated alkyl substances) from water.

PFAS are a large body of fluorinated chemicals, found in waterways and in the environment globally, due to industrial production over the last fifty years. More recently we have started to identify their toxicity and their bioaccumulation potential. They don’t degrade for thousands of years, so once they are put into the environment, they stay for a long time. A study was done a few years ago, it ends up that 98% of Americans have some detectable amount of PFAS in their blood at any one time.

We developed this resin technology, the easiest way to explain this, it’s very similar to granular activated carbon, or ion exchange resins. It’s a material you put in a column, similar to the BRITA water filter. There is a column of material you pass water through, and our material specifically targets the removal of PFAS. This is the key difference compared to previous technology. Most technology in water purification is broad-spectrum, made to absorb everything. 

As PFAS is a particular problem at low concentrations, we rethought how to go about designing the material to targets this one contaminant specifically, allowing us to perform better remediation of the substance.

Why we did this, the state of NC has a particular problem with this. In 2016 it was discovered that one of our largest rivers, which feeds into and provides drinking water for our third largest city and many other municipalities had alarmingly high levels of PFAS, generated from an industrial site dumping the material upriver. This caused a lot of concern as one might expect. It prompted the state, and state legislature to start looking into this, looking at funding the testing of the materials and generation of technology to help remediate this. It was the concern of the state, and us being a state institution that this came by my desk. Being a polymer chemist, I have the expertise to design material from the bottom up to solve this problem.

WT: One of the big issues around wastewater and drinking water is the use of granular activated carbon; this is the stuff counted on to take out pollutants. I understand that once the activated carbon is saturated, it doesn’t work at all, and it has to be replaced many more times than is currently required by industry regulations. How did you figure this out, and what does your solution offer for this problem?

Leibfarth: This PFAS pollution problem is very much a modern problem, a consequence of modern society, yet our answer to solving this problem is to pass water over what is basically burnt wood. It makes sense for a modern problem to have a modern engineered solution. The granular activated carbon is made from natural materials, it’s very inexpensive, which is one of its advantages. The limitations of it come back to the idea that this material was developed to be a broad-spectrum absorbent. It absorbs organic matter, it absorbs a number of ions commonly found in water, heavy metals, also some PFAS.

The challenge is, PFAS are extremely toxic at low concentrations, single-digit per trillion concentrations. Where you have just natural organic matter in most ground and surface water that is anywhere from a thousand to a hundred thousand times more concentrated than the levels of PFAS in the water. Because activated carbon absorbs everything, it quickly becomes saturated by the organic matter, which binds stronger than PFAS, so the small amounts of highly toxic PFAS get kicked off by organic carbon. When you use granular activated carbon for PFAS specifically, it does not last very long, you are replacing the material every year, hundreds of pounds of material. Traditionally with organic matter and metals, you are getting two to three years out of the same materials. So, this is resource-intensive, costly, especially for short-chain PFAS which are of great concern, it just doesn’t work that well.

WT: If I read the research right, your process relies on fluorine. Your team has invented a “fluorinated ion exchange resin”. When people hear fluorine, I would expect they would think fluoride. Is this the same base? Can you explain the inner workings of what your team has come up with?

Leibfarth: Exactly right, we rely on what are known as “fluorous interactions”. Fluorous compounds are really interesting. You know if you put oil and water into a beaker, it will separate into two layers. If you put a fluorinated oil into that same beaker, it will form a third layer. They don’t really like water, they don’t really like oil, they like each other.

This is the interaction we took advantage of to get this really high selectivity for PFAS. 

Fluoride is F-; it is a fluorine atom that is negatively charged and is then soluble in water. It has a free lone pair of electrons, allowing it to form ionic bonds with hydrogen or sodium or other positively charged ions. 

This is very different than fluorine, which is covalently bound to a carbon atom, which is what is in our resin. So that is not charged, completely insoluble in water. The carbon-fluorine bond is one of the strongest bonds known, strongest on the periodic table. One of the problems with PFAS is that the carbon-fluorine bond is almost impossible to break, so we are not worried about fluoride coming off our materials because we have this advantage.

What we are very focused on, PFAS are fluorinated compounds. We are taking advantage of this fluorous interaction for our resin. That means we need to ensure that by producing this resin, we do no harm. We use fluoropolymers that can be produced without producing more PFAS, made without fluorinated surfactants. We have done extensive testing in collaboration with organizations like EPA to ensure that our materials do not degrade, even in the harshest conditions that they would find in a water treatment scenario.

WT: One of the things I find most interesting about this, that PFAS are negatively charged. Is that where the ion exchange comes in, trying to influence this negative charge?

Leibfarth: Yes, absolutely. Ninety-five plus percent of the PFAS you typically find in the environment, at least in water, are negatively charged. We leverage the simple electrostatic interaction, we put positive charges on our insoluble resins. That’s the same concept as commercial ion resins.

With the addition of this fluorous interaction in our material, we find the two work together for mass transport into our material, so that it sticks around there. So, it’s not just the ion exchange, it’s the synergistic effect of both (ion and fluorous) interactions happening at once, in the same place.

WT: Using your team’s know-how, if I am a wastewater plant operator or water plant operator, and I use your process when I end up with a pile of PFAS, then what? Do I burn it? How do I get rid of it?

Leibfarth: Yes, that is a critical challenge in the field. Some ion exchange resins can be washed with a briny solution, you can wash a lot of that concentrated PFAS off the filter into a waste stream. So, what do you do with that? The current technology is either pyrolysis or plasma-based technology, essentially incineration. That mineralizes a fair amount of the PFAS, but unfortunately, some of those are released into the atmosphere, where they eventually deposit back on the ground.

What I am excited about, and my group has thought about this, the emerging technologies that can take advantage of the concentrated waste stream of PFAS and degrade it through novel chemical mechanisms. This is still a challenge in the field, it is not solved, but there are some great groups working on it. I think the ability to concentrate PFAS in a waste stream, gives the technology that can actually destroy it a chance. 

WT: You have three test sites, one is especially interesting from our point of view – PFAS detected in a well, so that means PFAS is in the aquifer. Can you talk about the test sites you are working on?

Leibfarth: Yes, one will be at a municipal wastewater treatment plant at the mouth of Cape Fear River near Wilmington; this has been the hotbed of PFAS remediation in the states. They have a lot of technology; they have run a lot of pilot tests. We just talked to them last week. It’s exciting because they know how to test technology, they have benchmarks for their water.

The second will be at a wastewater treatment plant significantly upriver. It has been found through testing, sponsored by the North Carolina Collaboratory, that was part of the effort our group was initially supported by, that this wastewater treatment plant is a point source for a lot of PFAS in the state. So, that runs from upriver of me, so I am affected by that in my own home, all the way down to Wilmington. Cape Fear is the catch-all for a lot of this pollution. Wastewater treatment is a really big issue for PFAS, because a lot of industrial water, a lot of run-off, water that is used where PFAS is concentrated is sent to wastewater treatment plants, so remediating it there, can prevent it from getting out to the environment.

The well site, I am still learning about it myself. All these three sites were mandated in the law that was passed, that provided our funding. It was the legislators in NC that led the effort to find the technology we have created, pushing us to think about it to the next level and test it in real-world scenarios. They were pumping excess surface water down into the well, I think it’s called groundwater reclamation, this was done before the challenge of PFAS had been identified. When we did testing, that aquifer was found to have a really high level of PFAS, so was shut down, not being used for consumption. They are really interested in the long-term impacts, looking to see if we can pump out the water, take the PFAS out, and pump it back down. If we can do that, there might be some incentive to rethink how to do reclamation projects and maybe get them back on-line.

WT: I looked into the Intellectual Property laws, this can become a sore point for research teams at different universities in Canada and the USA. I see that in your project, the intellectual property stays with UNC Chapel Hill to fund future research. Was that your decision, was it a team decision, or did the UNC decide?

Leibfarth: This is a complex topic. I want to reiterate, one: we have not started a company yet. The funding from the state sits with the university. So, if we do choose to start a company, the project that is mandated by state law will still occur through the university. For numerous legal reasons, I want to make that clear. 

Second, if we, or a different entity would want to license the technology, like everything I invent as an employee of the university, the technology is owned by UNC. Typically myself, any students or collaborators that made contributions are listed as co-inventors. Any business that comes of this, negotiates the rate to be paid for the license fee; 2 to 5 % of the revenue generated by the technology annually. The licensing agreements require that a percentage of funds generated by the invention is sent back to the University. 40% of that is distributed to the co-inventors, so the students do get some of the revenue from the IP.

What is different, the specific aspect of this put into the state law, concerns the 60% that goes to the university. In this case, the 60% is split differently. A portion goes back to the Collaboratory to fund more PFAS research, a portion goes to the general assembly to “payback” the money invested in our research, the rest gets split between our department and others in the university.

WT: Has anyone mentioned being nominated for Nobel prize for this work?

Leibfarth: Oh my gosh no! The Nobel is typically given for fundamental advances. This work is rather applied, for something like that.

WT: Frank, thanks for doing this, I appreciate this.


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