The DoD has nearly 4000 aqueous film forming foam (AFFF) delivery systems in aircraft hangars and on firefighting vehicles. To minimize future impacts, current AFFF formulations will be replaced with PFAS-free alternatives. During this switch over, significant amounts of PFAS containing rinsate will be generated as existing systems are cleaned. Therefore, it is critically important to develop a method to treat AFFF-containing rinsate.
The overall objective of this project is to demonstrate operation of a mobile plasma treatment system for the treatment of AFFF rinsate from firefighting delivery systems such as aircraft hangars or aircraft rescue and firefighting (ARFF) vehicles at DoD facilities. Specific aims include:
- Obtain and characterize samples of current use AFFF contained in firefighting delivery systems,
- Optimize the enhanced contact electrical discharge plasma reactor for treating AFFF-containing rinsate solutions,
- Determine if pre-oxidation of high concentration AFFF solutions with ultraviolet (UV) light activated persulfate, ozone, peroxone, or UV-hydrogen peroxide would be beneficial in terms of treatment time, destruction efficiency and cost,
- Modify the existing 20 ft long trailer to deploy the optimized reactor with preoxidation if it is determined to be beneficial, and
- Test the system using rinsate from a government-furnished ARFF vehicle.
Electrical discharge is a technology that, using only electricity, converts an otherwise inert fluid such as water into a mixture of highly reactive species including hydroxy radical, oxygen, hydrogen radical, perhydroxyl radical, superoxide anion radical, hydrogen, oxygen, hydrogen peroxide and aqueous electrons, called a plasma. The Clarkson University-developed next-generation enhanced contact (EC) plasma reactor operates on this principle and incorporates several innovations aimed at targeting per- and polyfluoroalkyl substances (PFAS) in a variety of water sources. A key innovation of the EC plasma reactor is the submerged gas diffuser, through which argon gas is pumped, to produce bubbles that concentrate PFAS at the gas-liquid interface where reactive species in the plasma are produced. Key benefits of the technology include: 1) rapid (minutes) destruction of PFAS and other compounds (e.g., volatile organic compounds , 1,4-dioxane); 2) no chemical additions and no production of residual waste; 3) preliminary cost estimates are >50% less than operation of granular activated carbon filters; and 4) the technology can treat both high and low concentration PFAS containing liquid streams.
In recent experiments, plasma treatment of 6 carbon atom-AFFF in a one-liter reactor for one hour resulted in production and then removal of long-chain perfluoroalkyl acids (PFAAs) and an increase in concentration of short-chain PFAAs and 6:2 fluorotelomer sulfonate. The starting viscous fluid was extremely foamy, so bubbling argon to transport PFAAs to the surface near the plasma was impossible. However, plasma treatment of a 10x diluted sample that had been pre-treated for 30 minutes with heat-activated persulfate to oxidize precursors prior to the treatment was able to rapidly remove long-chain PFAAs and precursors. Short-chain PFAAs and precursor concentrations increased initially and then stabilized or slowly decreased.
The validated electrical discharge plasma technology of this project addresses an urgent need by providing the DoD with an effective and efficient technology for degrading PFAS. Unlike sorptive technologies, it generates no waste that needs to be disposed of, limiting future liability. Substantial cost savings will be realized with the implementation of this technology.