Non Technical Summary
Per- and polyfluorinated alkyl substances, whose origins date back to the 1940s, are a class of compounds possessing high thermal and chemical stability. The compounds have been used in a range of consumer products owing to these robust properties. Their unusual stability and thus long half-life have led to the proliferation of these compounds in the environment. It is now well established that ingestion of these chemicals can lead to the development of a range of health disorders from endocrine disruption to cancer. Regulations at the federal and state level are setting health advisories of maximum acceptable concentration levels. Unfortunately, conventional water treatment systems cannot remove PFAS. The recalcitrant nature of these compounds, owing to the strength and shielding effects of the carbon-fluorine bonds, makes destructive removal difficult. Membrane treatments and activated carbon are capable of removing PFAS effectively, but each creates a concentrated waste stream. The US EPA identifies a research gap for low-cost methods to process concentrate streams from membrane processes or cheaper methods to regenerate activated carbon. The effort proposed here aims to use plasma to destroy PFAS compounds, both in contaminated water systems and in concentrate streams, derived from membrane processes. While it is widely recognized that plasmas are effective at destroying PFAS, the consensus is that work needs to be done on scaling up the process and quantifying overall implementation and operational costs. To date, plasma reactors--even the large ones--have been predominantly batch-mode reactors. It is desirable in industrial or municipal applications to treat water in a flow reactor configuration. Our goal is to investigate the feasibility of a once-through, scalable flow plasma reactor capable of treating practical influent flows. PFAS removal via plasma treatment is predominantly a surface treatment process--essentially long chain hydrophobic PFAS compounds are degraded by energetic electrons, ions, and UV light exposure. Considerable destruction is initiated via reduction by solvated electrons derived from the plasma where electron addition leads to spontaneous bond cleavage and defluorination. To destroy the PFAS with plasma, multiple exposures of the liquid surface are required to reduce the contaminants to smaller chains and ultimately to cause mineralization. In this regard, one must circulate the volume of water to be treated past the plasma multiple times as in a batch reactor. This proposal aims to convert from batch-mode explored in previous experiments to a flow reactor geometry while preserving batch mode kinetics. We hypothesize that using a series of reactors with recirculation such that water exposure to plasma matches the contact time in our batch reactor, we can achieve similar degradation in a flow-through geometry. Removal is achieved through serial processing of the water as it passes from one microreactor to the next so that the water receives the requisite number of passes through the plasma over the characteristic time constant as realized in a batch reactor. Furthermore, we will use reverse osmosis concentrate as our input feedwater. This PFAS load is degraded to desired levels at the end of the final microreactor where that water is blended with RO permeate to achieve the desired MCL, thus realizing a true flow-through reactor. The scalability of this system will be explored through the addition of parallel legs of microreactors. In all cases, the kinetics through a given flow reactor will match the exposure realized in the batch reactor from previous work. Understanding the scalability of plasma-based water treatment systems can provide a significant commercial and societal benefit. If the technology proves scalable, there are several commercialization applications for water quality management, particularly in areas of high concentrations of PFAS, or those amenable to RO pretreatment processes.

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
111	0210	2020	100%

Knowledge Area
111 - Conservation and Efficient Use of Water;

Subject Of Investigation
0210 - Water resources;

Field Of Science
2020 - Engineering;

Goals / Objectives
The effort proposed here aims to use plasma to destroy PFAS compounds, both in contaminated water systems and in concentrated streams derived from membrane processes. While it is widely recognized that plasmas are effective at destroying PFAS, the consensus is that work needs to be done on scaling up the process and quantifying overall implementation and operational costs. To date, plasma reactors--even the large ones--have been predominantly batch-mode reactors. It is desirable in industrial or municipal applications to treat water in a flow reactor configuration. Our goal is to investigate the feasibility of a once-through, scalable flow plasma reactor capable of treating practical influent flows.The main objectives for the Phase-I effort are listed below:Fabricate a three micro-reactor plasma treatment module with continuous flow processing capabilityTest the hypothesis that the combination of high-speed recirculation integrated in our batch reactor with reservoirs coupled in series can treat water in a once-through fashion down to levels approaching the EPA maximum contaminant levels for PFASAssess the validity of the tanks-in-series model applied to a reactive flow system for predicting the performance of the continuous flow plasma treatment system using batch-mode kinetics

Project Methods
Spiked and actual groundwater samples will be analyzed using an in-house liquid chromatography mass spectrometer. PFAS analysis will be conducted using a modified EPA Method 537.1. Briefly, samples will be concentrated using solid phase extraction, and quantified using a Liquid Chromatography/High resolution QExactive Orbitrap (Thermo Scientific). Twenty-four PFAS compounds (EPA Method Development Analyte List) will be quantified. In addition, the high-resolution mass spectrometer will enable us to qualitatively assess the presence of unknown PFAS compounds in samples, and the effect of plasma treatment on PFAS speciation within the same analysis. Additional water quality parameters, including pH, conductivity, total dissolved solids, and residuals that form during plasma treatment (e.g., nitrates) will be monitored using their respective EPA standard methods. Power deposited into the plasma will be monitored using current and voltage diagnostics. This will allow us to assess the decomposition efficiency of the treatment process.