Peter Jaffé is the William L. Knapp Professor of Civil Engineering and Professor in the Civil and Environmental Engineering department. Earlier this week, I conducted an interview with him regarding a recent research project on removing a pollutant called PFAS or Per- and poly-fluoroalkyl substances, a topic of great concern among composters. In the summary of the interview below, I ask Professor Jaffé about these pollutants and the bacteria that can remove them.
Q: What are PFAS and why is it important to develop methods to remove them?
A: It stands for per- and poly-fluorinated substances. There are about 4000 different fluorinated compounds that the chemical industry has manufactured. They are interesting because the carbon-fluorine bond is the strongest covalent bond in organic chemistry, which gives them a lot of stability, and as such the compounds have been used to create water and heat resistant products. Two main compounds are perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). PFOS was developed by 3M which makes Scotchgard a water repellent spray and is also used as firefighting foam. PFOA was developed by DuPont to make Teflon which is a long carbon-fluorine polymer, commonly used in non-stick cookware. These molecules are a big challenge because they were built to be stable and they have no easy analog in nature so organisms haven’t evolved to degrade them so now there are health effects that we associate with them. They have developmental effects and are possibly carcinogenic, and lead to kidney diseases. They have been used quite aggressively since post-WWII and we haven’t really tracked them very much. It was only in the last decade or so that we became concerned about them.
Q: What other types of products can you expect to find PFAS in?
A: They are in all kinds of consumer products, because when they stick to something they become water repellent. Pizza boxes have PFAS so that they don’t get too wobbly too quickly, so do cardboard food plates. Any rugs that are stain resistant, some of your clothing, airplane parts…you name it. It is pretty much everywhere.
Q: How did you discover that Acidomicrobium bacterium A6 was able to remove PFAS?
A: We first noticed that there is a process for oxidizing ammonium to nitrite in anaerobic sediments under iron reducing conditions. After we first published this finding, other researchers noticed the same including a Japanese researcher who found something similar in a reactor. They called that process Feammox which is an analog to anammox, another anaerobic ammonium oxidation process that we were studying. A microbiologist that we were working with managed to identify the organism that is responsible for this oxidation, Acidomicrobacterium A6. She managed to then grow it in a pure culture and do genomic sequencing.
Looking at the sequencing, we noticed that it had a series of interesting genes, some oxygenation related, and those seem to be linked with the process of ammonium oxidation. Later we noticed that it had some sequences for dehalogenase enzymes. We said, “Ah, let’s try and see if we can do something with PFAS” and lo and behold we tested it and it could defluorinate them, at least most of those we have tested. There are some highly branched ones that we have difficulties with but almost everything else we can defluorinate, which is pretty stunning because so far there has been no other organism that has been shown to defluorinate the perfluorinated ones. There are some organisms that can take a single fluorine out when you have some carbon-hydrogen bonds and some carbon-fluorine bonds, but when you have no hydrogen bonds and it is all fluorine bonds so far this is the first one that has been identified.
Q: What are the limitations of using A6 to remove PFAS and how are you planning to overcome those limitations?
A: From a technological point of view, it’s an anaerobic autotrophic organism so it grows very slowly. The doubling time is somewhere between 10 to 14 days as opposed to E. coli which could be half-a-day or fewer. Anytime you have to deal with a bacterium that grows slowly that becomes hard. Another problem is that when we want to grow it in a reactor it uses ferric iron and the stoichiometry is 6 irons per ammonium assuming 100% efficiency (and it’s not 100% efficient) so the amount of iron in minerals that you have to add is large. Plus a goop of magnetite ferrihydrite will build-up in the reactor and you cannot keep running it. So the challenge is how can we keep growing this organism without iron? We have shown that it can be grown in microbial electrolysis cells, but the challenge is how do we go from these little vials to a continuous flow reactor. We are struggling with that right now.
Q: Are there any implications related to composting or potential testing opportunities with the S.C.R.A.P. Lab?
A: Since there are PFOA precursors in pizza boxes and paper plates, if they are composted, then you’ll have PFAS in the compost, and then you will certainly not want to use the compost as a soil amendment because plants will take up the PFAS. It is something that the university should look at, but the unfortunate thing is that these analyses aren’t cheap. If you send the sample to a commercial lab, one analysis is about $450 so you want to think carefully before you spend too much money.
Q: And how does your project seek environmental justice?
A: Not directly but there are of course usually lower-income neighborhoods in locations close to industrial facilities where firefighting foam has been used so I would say that you have PFAS proportionately higher in lower-income neighborhoods. The highest PFAS are typically around military installations because they use a lot of firefighting foam in the hangars where they put planes in. I am not sure if this is still done today but in the past, these facilities would perform tests where they fill the whole hangar with foam in case a plane catches fire or something and the foam runs out and spills into the groundwater. So yes it is likely that concentrations of PFAS are higher in groundwater close to facilities so in that sense coming up with a methodology to degrade them is an indirect way to address environmental injustice.
Professor Jaffé ended the interview by stating, “I’m excited about the work. We’re excited about this organism that could oxidize ammonium, but we’re excited to have one that can target the most complicated contaminants. I have 4 new Ph.D. students coming this year and all of them want to work on different aspects so we’ll have quite strong activity in the next couple of years.”