By Emily Loder, WMEAC Policy Intern
Per-and polyfluoroalkyl substances (PFAS) are a group of harmful man-made chemicals that have been present in thousands of everyday products since the 1950’s. PFAS have been found at increasingly high rates in our waterways due to manufacturing and improper waste disposal. The current best practice, and most readily available options, for treating drinking water containing PFAS are filtration methods such as reverse osmosis (RO) or granular activated carbon (GAC). These solutions, however, only remove PFAS from the water. The toxic chemicals remain in the filters, which can re-contaminate an area if there is not proper disposal or regeneration of the waste materials. New technologies are being developed that can completely destroy PFAS chemicals, instead of just filtering them out of water. Methods that destroy PFAS chemicals leave little-to-no risk for recontamination when compared to traditional filtration methods. Two of the promising innovations are supercritical water oxidation and plasma technologies. Contact experts like this Dayton plumbing company to upgrade your plumbing system as well as to inspect your water quality via your plumbing fixtures and other things like plumbing huber.
Supercritical Water Oxidation
Supercritical water oxidation, or SCWO (pronounced sc-woah) is a method of treating water through the application of high pressures and high temperatures. This transforms water into supercritical water, a substance that has properties of both a gas and a liquid. Oxygen (O) is fully soluble in supercritical water, meaning that the oxygen atom detaches from the hydrogen atoms. In other words, the O leaves the H2O. The next step in SCWO is the oxygen attaching to carbon atoms to form carbon dioxide (CO2), which is called oxidation. PFAS chemicals are made up of long chains of carbon atoms so there are lots of opportunities for oxidation. Using SCWO on water contaminated with PFAS results in the complete oxidation of the PFAS molecules, which destroys them by breaking all the chemical bonds. The final products of the SCWO method are clean PFAS-free water, carbon dioxide, and salts. Carbon dioxide and various salts are naturally found in most waters, so those by-products are not a cause for concern.
One of the big benefits of SCWO is the speed and effectiveness of the process; complete destruction of PFAS compounds to non-detectable levels can occur in seconds. Battelle, an Ohio-based nonprofit organization, is working on developing mobile SCWO units that can be deployed across the country to treat water at PFAS sites. The technology can treat both surface water and groundwater at these sites. Battelle has dubbed their SCWO technology the “PFAS Annihilator,” and they have a unit that can treat up to 500 gallons of water a day. A larger unit that can treat up to 5,000 gallons per day is also in development. Although it may seem like these units would be energy-intensive, that is not the case. Battelle’s PFAS program manager, Amy Dindal, stated in a December 7, 2021 U.S. congressional hearing that their mobile PFAS Annihilator unit can be plugged into home power or can run off a generator. In May 2022, Battelle deployed PFAS Annihilator to a site in West Michigan. Battelle is also working with Grand Rapids waste management company, Heritage-Crystal Clean, Inc., to scale up the Annihilator technology for widespread use. SCWO is a powerful tool that can be used in tandem with other methods like GAC to treat higher volumes of water. These facilities may also use a steam generator to aid in the water treatment process.
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Plasma Technologies
“Hopefully our work here can move forward and get useful technology to destroy PFAS.”
The Michigan State University PFAS Research Lab, headed by Dr. Qi Hua Fan, was recently awarded a ~$700,000 grant to test new plasma technologies for destroying PFAS from the Great Lakes Protection Fund (GLPF). The research is being conducted in partnership with Fraunhofer, Europe’s largest applied research organization. Plasma is a distinct fourth state of matter, separate from the commonly known solids, liquids, and gasses. Plasma is an extremely hot (around 30,000 degrees Celsius) and extremely energetic state of matter, similar to a superheated gas. Recently, I was given the chance to visit the PFAS Research Lab and to speak with Dr. Fan about the innovations happening within their walls.
The new technology that Dr. Fan is working with is called Magnetically Enhanced Arc Plasma (MEAP), which he believes is superior to the predecessor technology, arc plasma. The process begins with gas being pumped into a container of PFAS-contaminated water, which causes it to bubble. The gas bubbles in the water trap PFAS molecules and transport them to the surface. This is where the plasma comes in. MEAP creates a “disc” of plasma that sits above the water’s surface. As the gas reaches the surface, the plasma arcs toward the gas bubbles and destroys the PFAS molecules trapped inside with intense heat. Since the plasma “disc” spans the entire surface area of the water, no matter where the gas bubble emerges, the plasma is able to intercept it.
Dr. Fan calls the process of interception a dynamic discharge. “This dynamic thing can really cover a wide range of surface area, it automatically covers a large area” as opposed to the previous arc plasma technology that was very localized. MEAP completely destroys PFAS molecules, while the previous arc plasma method ran the risk of only partially destroying PFAS molecules as it was ineffective at destroying smaller PFAS molecules. “It is much more effective than the arc technology,” Dr. Fan says about MEAP, “this is a very promising technology to move forward.”
The PFAS Research Lab is currently working on scaling their technology; right now they can only treat small volumes of water but are hoping to increase the treatment capacity of MEAP. They “are going to develop prototypes from 100 milliliter, to 1 gallon, and then 100 gallons.” The goal is to eventually incorporate the plasma technology into wastewater treatment plants, as MEAP is not necessarily a technology that can be deployed to PFAS contamination sites. Dr. Fan hopes that their plasma technology can be used along with other technologies to create a comprehensive treatment and destruction plan. “I wouldn’t say this [MEAP] is the only solution, I think there should be many different technologies coexisting.” For example, SCWO, featured above, can be used to treat PFAS at the source and plasma can be used to prevent PFAS from moving through the municipal water supply system.
After our conversation, Dr. Fan took me around to the research labs where the plasma technology is being tested, and I got to see an experiment in process. They typically expose the water to plasma for 10 minutes. After they apply the plasma, the water is sent to an independent laboratory to test the PFAS concentration remaining in the water after treatment.
Other Innovations From Battelle and MSU
Battelle has also developed some other technologies and methods for eliminating PFAS.
Granular activated carbon (GAC) filtration is a very common method for treating PFAS-contaminated water, but the carbon eventually becomes saturated with PFAS and must be reactivated. Reactivation is typically done thermally, an energy-intensive process that exposes the GAC to extremely high temperatures. All the PFAS that were captured in the GAC get destroyed once they are exposed to high heat for a prolonged time. After the PFAS is destroyed by heat, the GAC can hold contaminants again and is able to be reused. Through the reactivation process, some of the original GAC compound gets destroyed and must be replaced with new GAC. Battelle is developing an alternative to the traditional thermal reactivation which uses a lot of energy and creates some waste. Battelle created a liquid regenerant that “washes” the GAC and removes the PFAS without destroying any of the GAC compound. After washing, the regenerant solution is treated with PFAS Annihilator. Typically the saturated GAC compound is completely removed from the filtration system and sent away for regeneration, interrupting the filtration process. Battelle’s GAC regeneration system has a two-tank design that allows filtration to stay online while regeneration is happening.
PFAS does not only exist in water; PFAS can also contaminate soils which are much more difficult to treat. Battelle currently has a two-step method for treating soils, and they are working on developing a new, one-step method. In a December 7, 2021 U.S. congressional hearing, Amy Dindal spoke about Battelle’s solutions for PFAS in soils. The current method is to wash soils with a mix of solvents to get PFAS into an aqueous solution. This simply means that the PFAS compounds are suspended or dissolved in water. Once the soils are washed, the PFAS Annihilator technology can be used on the aqueous solution to destroy the contaminants. Battelle is also reportedly working on a technology that can clean PFAS from solid soils with no washing necessary, but there is no additional information on that project at this time.
Dr. Fan also told me that the PFAS Research Lab, in collaboration with Fraunhofer, is developing their own method for GAC regeneration which utilizes plasma. Their technology involves pushing the spent GAC compound through a tube and treating it with plasma to destroy the PFAS trapped inside the carbon.
