The ComPOSTer: Interview with Professor Z. Jason Ren

Professor Zhiyong (Jason) Ren is a Professor in the Civil and Environmental Engineering Department and is the Acting & Associate Director for Research at the Andlinger Center for Energy and the Environment. I had the pleasure of being his student in the Fall of 2019 in his class Resource Recovery for a Circular Economy. He recently started a project with Professor Anu Ramaswami on developing new methods and technologies to manage food waste in our society. In this interview, I ask him what this project is and how it relates to the circular economy, the S.C.R.A.P. Lab and environmental justice.

Professor Zhiyong (Jason) Ren; Source:

Q: How does the work that you are doing relate to the circular economy?

A: My research is very much related to it. When you talk about the circular economy you talk about the 3 R’s: recycle, reuse, and reduce. I am more on the reuse side because we are trying to improve the values of the waste and convert it into a value-added product. Not to mention that in this project we try to actually make better value-added products out of traditionally low-price products. This has been a challenge in waste valorization. If you actually can make profits using technology made of waste material that makes economic sense then that makes the technology more applicable in the real world.

Q: Can you describe the work you are during with Professor Ramaswami?

A: Professor Ramaswami and I along with other professors in other universities have been issued an INFEWS (Innovations at the Nexus of Food, Energy, and Water Systems) award from the USDA. My part of the work is looking into the technological advancements of treating food waste generated from different places and developing technologies to convert food waste to make better products. Especially if there is any possibility to produce biogas which is a cheap energy source. We’re also looking at the possibility of biochar which can enhance the anaerobic treatment process to produce energy, water, and fertilizer from food waste and hopefully then go back and actually put these resources back into community gardens. So it is a closed loop utilization of food. That’s my side of the project and we’ll work with Professor Ramaswami’s group analyzing the benefits and challenges of different technologies by using life cycle assessments and economic analysis tools to understand the system.

Q: Why do we want to develop new methods of managing our food waste?

A: Because it’s a problem, that’s for one. Food waste certainly occupies a lot of landfills, and we should not have a lot of food waste anyways because we do not want to waste a lot of food. Secondly, if we have to generate food waste we have to give it a better use. You don’t want to just throw it away and leave it rotting somewhere like a landfill which causes different issues. It would be better utilized for beneficial use which is basically the principle of a circular economy.

Q: How does the S.C.R.A.P. Lab fit into your project?

A: The campus composter and facility is a very important demonstration tool to campus as an educational tool and also is a good approach to convert campus food waste into something valuable. It is certainly a good example of waste valorization.  On the research side, this approach compliments what we do because the technology developed in my lab is not at the scale of commercial application yet. The S.C.R.A.P. Lab serves as a benchmark to which  alternative waste valorization technologies like producing protein out of food waste may be compared against. Other things can actually be in collaboration with the compost facility. It is a very important facility for our community.

Q: How would our current system for handling food waste contribute to environmental injustice? And how does your project seek environmental justice?

A: Currently a lot of food waste goes to landfill so you see how unpleasant those places are and certainly everyone has a notion of “Not in my Backyard” (NIMBY), don’t build a landfill in my backyard. I would assume most of these landfills would be closer to land and neighborhoods that are lower income and are disproportionately disadvantaged communities. So you would help to reduce those types of construction and reduce the impact on some of these communities. And from the economic side you could develop technologies to make waste a valued product that creates a lot of job opportunities and businesses within the waste management industry. As a result, waste companies can use these technologies which will create circular economy jobs that pay better and generate revenue products itself which will be economically beneficial as well.

The ComPOSTer: Interview with Professor Peter Jaffé

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.”