Formatted Title
Field Demonstrations of Enhanced Contact Plasma for PFAS Destruction: Lessons Learned
Background/Objectives
Cleaning up sites where poly- and perfluoroalkyl substances (PFAS) have spilled, leaked or been disposed of will be a billion-dollar industry in the United States with thousands of sites undergoing or scheduled for remediation. For this class of chemicals, conventional groundwater and soil cleanup systems are largely proving to be ineffective. Several novel treatment approaches are being explored including some that are able to break down these compounds. However, to date, only few PFAS destructive technologies have been demonstrated in the field. Enhanced contact plasma reactors for PFAS destruction were initially developed at Clarkson University and are being commercialized by DMAX Plasma Inc.. They have been installed into mobile trailers and successfully demonstrated in the field at several locations. In this presentation, an overview of the technology and results from field demonstrations using this technology will be presented.
Approach/Activities
The plasma technology uses electricity to convert water into a mixture of highly reactive species (i.e., plasma) that rapidly and non-selectively degrade and a broad spectrum of PFAS including perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and shorter-chain PFAS. The plasma reactor can simultaneously oxidize and reduce organics by producing a mixture of OH radicals and aqueous electrons, the latter of which act as strong reducing agents and are the key species in removing PFAS and other non-oxidizable compounds. Additionally, the plasma process requires no chemical additions and produces no residual waste, although in some applications surfactants are added to enhance short and ultrashort chain removal. The ECo-PRe™ uses multipoint high voltage electrodes for the generation of plasma. Gas diffusers are positioned on the bottom of the reactor and argon gas is continuously pumped through the diffusers producing bubbles and forming a layer of foam on the liquid surface. This foam concentrates PFAS and enhances the contact between the liquid and the plasma, exposing the PFAS at the interface to reactive species in the plasma.
Results/Lessons Learned
Extracted groundwater, still bottoms produced from the regeneration of ion exchange regenerant, AFFF rinsate generated from the cleaning of fire trucks and nanofiltration membrane concentrate, all from DoD sites, have been treated in the field using this technology. Depending on initial concentrations either batch or flow-through mode was used. Flow-through mode used flowrates of up to 10 gpm. In all cases, regardless of the source water, removal rates of long-chain perfluoroalkyl acids and PFAS precursors (fluorocarbon chain ≥ 6) were rapid with concentrations rapidly reaching non-detect levels. Shorter chain removal rates were slower, however the addition of a cationic surfactant significantly increased removal rates. If treatment continued long enough, their concentrations also reached non-detect levels. The treatment trailers have been significantly upgraded with improved reactor design and automation to allow them to operate unattended. An overview of the technology and results from these field campaigns will be discussed in this presentation.