PFAS consist of many compounds with varying molecular size, structure, and functional groups. It is likely that most of the PFAS ever produced still exist as fully-fluorinated compounds. The high energy carbon-fluorine bonds within PFAS molecules make them extremely stable and resistant to chemical, biological, and thermal degradation. As a result of their stability, PFAS are persistent in the environment and are known to bioaccumulate in humans and other species. PFAS contaminated drinking water is reported to be an important route of human exposure. The presence of PFAS in drinking water has been linked to industrial emissions, military fire training releases, landfills, and incomplete removal in wastewater treatment plants.

The same properties of PFAS that account for their persistence and stability in the environment also limit the treatment options of water suppliers to remove PFAS from water supplies. Adsorption processes, including filters containing granular activated carbon media, are among the most cost-effective removal processes used by water utilities. Destruction technologies for PFAS have been the subject of a growing number of research studies. Approaches with the most success have generally involved the use of combinations of physical technologies, such as heat, UV light, or microwave technologies with chemical agents, such as strong oxidants or catalysts. Alternatively, they involve energy intensive methods, such as high-voltage electric discharge, supercritical fluid, or ultrasonic treatment. These technologies, however, have not yet been proven or applied in the field, either because they generate toxic by-products, smaller chain PFAS, or potent greenhouse gases, or they are relatively expensive. Traditionally biodegradation using microorganisms has been a cost effective method of destruction for many organic compounds, however, it is ineffective for PFAS.

At the University of Michigan, Dr. John Foster’s laboratory in Nuclear Engineering and Radiological Science (NERS) has been testing several plasma reactor designs for various environmental contaminant mitigation applications for a number of years. In 2019, Dr. Terese Olson, in UM’s Department of Civil and Environmental Engineering (CEE), approached Dr. Foster about collaborating on a PFAS treatment approach combining his plasma work with her expertise in water treatment.

In late 2019, the Urban Collaboratory introduced this research team to the Revitalization Auto Communities Environmental Response (RACER) Trust who manages a number of PFAS impacted sites across the country including two in Michigan. One site, Willow Run, is the location of Ford’s former B-24 manufacturing facility in Ypsilanti Township. The other, Buick City, is the site of a former GM manufacturing facility located in Flint. Working collaboratively with RACER, the UM team secured a supply of a moderate concentration PFAS waste stream from Willow Run and a relatively high concentration waste stream from Buick City, both in groundwater.

Plasma-based treatment relies on the production of reactive radicals, UV light, electrons, ions and excited species which form when a gas breaks down.  Breakdown typically occurs through the application of a sufficiently high voltage such that the sparking potential is reached, thereby facilitating the formation of an ionization wave. The ionization wave produces the plasma activated gas which chemically reacts with its surroundings. In contact with water, the plasma activated gas drives both advanced oxidation through the introduction of reactive species such as the hydroxyl radical and reduction through the introduction of solvated electrons and negative ions into solution. The team will test the use of plasma-based treatment in combination with a membrane treatment pre-concentration step to remediate PFAS in contaminated groundwater. Following bench scale laboratory work, the team implemented a pilot treatment system at the Willow Run facility. The near-term objective is to treat groundwater at the site to meet the new Michigan standards for seven specific PFAS compounds.