“Photocatalytic Destruction of PFAS in Investigation-Derived Wastewaters” by Dr. Ezra Cates (SERDP Project ER18-1599) 

This presentation focuses on the development of a deployable water treatment system with a capacity of 1 million gallons per day for treating investigation-derived wastewaters impacted by PFAS. Recent laboratory studies have shown that a number of semiconductor photocatalysts are capable of degrading and mineralizing PFAS. Bismuth-based materials, such as Bi₃O(OH)(PO₄)₂ (BOHP), are among the most promising and practical. Lab tests show that the PFAS removal rates may be fast enough for cost-effective treatment. However, photocatalytic water treatment is notoriously challenging to implement at larger scales, which are required for treating PFAS-impacted water. This presentation will cover lessons learned in scaling up the ultraviolet (UV)/BOHP process from simple, bench-scale UV photoreactors to a commercial photocatalytic treatment system. Aspects of photoreactor design, implications of different lamp types, and other behaviors significant to PFAS removal and to the broader field of photocatalytic treatment will also be discussed.    
 

“Physical Chemistry of PFAS-free Firefighting Foam” by Dr. John Payne (SERDP Project WP-2738)

Short-chain C6 fluorosurfactants give firefighting foams good stability and a positive spreading coefficient, but they only partially break down in the environment, leaving persistent PFAS behind (e.g., perfluorohexanoic acid (PFHxA)). Foams containing only hydrocarbon-based surfactants are expected to break down rapidly and completely in the environment, leaving no long-term effects. This presentation will discuss a project that analyzed the physical and chemical processes of firefighting foams in order to develop a PFAS-free foam that meets the fire performance standards of MIL-F 24385F. The team used equilibrium and dynamic surface tension, rheology and optical microscopy techniques to study foam properties and understand how foam components can generate the critical properties of spreading, stability and vapor suppression that are essential for good fire-extinguishing performance. Small lab-scale and full-scale fire tests were used to correlate foam properties with fire-extinguishing performance. A candidate formulation was optimized using statistical analysis to extinguish a 28 ft2 heptane fire in 36 seconds.  

Short-chain C6 fluorosurfactants give firefighting foams good stability and a positive spreading coefficient, but they only partially break down in the environment, leaving persistent PFAS behind (e.g., perfluorohexanoic acid (PFHxA)). Foams containing only hydrocarbon-based surfactants are expected to break down rapidly and completely in the environment, leaving no long-term effects. This presentation discussed a project that analyzed the physical and chemical processes of firefighting foams in order to develop a PFAS-free foam that meets the fire performance standards of MIL-F 24385F. The team used equilibrium and dynamic surface tension, rheology and optical microscopy techniques to study foam properties and understand how foam components can generate the critical properties of spreading, stability and vapor suppression that are essential for good fire-extinguishing performance. Small lab-scale and full-scale fire tests were used to correlate foam properties with fire-extinguishing performance. A candidate formulation was optimized using statistical analysis to extinguish a 28 ft2 heptane fire in 36 seconds.  

Dr. Ezra Cates is an associate professor of environmental engineering at Clemson University. Dr. Cate’s research focuses on the development of advanced light and radiation-based water treatment processes for disinfection and advanced destructive treatment. He has served as principal investigator on several projects seeking to develop cost-feasible destructive technologies for treatment of wastewaters containing PFAS. He has authored more than 20 peer-reviewed research papers and patents, as well as several key perspective pieces on photocatalytic water treatment. Dr. Cates earned a bachelor's degree in environmental studies from the University of North Carolina, Asheville and a doctoral degree in environmental engineering from the Georgia Institute of Technology in Atlanta. 

Dr. John Payne is the Foam Research and Development Manager at Angus International Safety Group, the parent company of National Foam, Inc. In this role, he develops PFAS-free firefighting foams and brings them to global markets for civil and military aviation, marine, fire and rescue, and petrochemical end users. Dr. Payne’s work focuses on understanding how the bulk phase and interfacial chemistry of foam formulation components affect foam properties and fire performance. He leads a team of scientists who have developed PFAS-free foams including Universal ® F3 Green 3%-3% and Avio ® F3 Green KHC that pass most international test standards, including ICAO B and C, UL162, LASTfire and EN1568. Dr. Payne has contributed to industry groups, such as the FFFC Analytical Workgroup, to develop an analytical method to measure PFAS in foam. He is a technical peer reviewer of the GreenScreen standard for firefighting foam, and he was also the industrial supervisor of a doctoral student at University of Bristol investigating hydrocarbon and fluorocarbon interactions at interfaces. Dr. Payne earned a bachelor’s degree in chemistry and a doctoral degree in physical chemistry from the University of Bristol.