(313b) Pfas Degradation By a Thin Film Gas-Liquid Non Thermal Plasma Reactor

Contamination of groundwater by per- and polyfluorinated substances (PFAS) is an emerging worldwide environmental problem and current water treatment methods for dealing with PFAS use the non-degradative methods of activated carbon and reverse osmosis for physical removal from the contaminated water. In the present work we utilize a non-thermal plasma chemical reactor to degrade the PFAS: 8-carbon (C8) (perfluorooctanoic acid – PFOA), 6-carbon (C6) (perfluoro hexanoic acid - PFHxA) and 10-carbon (C10) (perfluoro decanoic acid - PFDA). The non-thermal plasma, a type of ionized gas, is generated by a high voltage electrical discharge in a reactor with flowing gas (argon) and liquid (water). The plasma discharge channel propagates along the interface between the gas and the thin liquid water film where the generated reactive chemical species, including reductive and oxidative species, degrade the PFAS into smaller carbon chain daughter products and mineralization products such as carbon dioxide and fluoride (F-). We have quantified PFAS degradation, mineralization, and product formation for different feed concentrations (10 ppb to 1 ppm) in deionized water solutions and for water conductivity up to seawater. The effect of various parameters such as pulse frequency (kHz), liquid flow rate (mL/min), solution conductivity (mS/cm), and radical scavenger addition are investigated. The results showed that based on chain length of PFAS, a shift in optimal mineralization was observed. Longer chain length (C10) PFAS resulted in faster removal rates for than shorter chain length (C6). Through optimization of the plasma reactor operating conditions (pulse frequency and pulse width) we have achieved 90-75 percent degradation of these selected PFAS. Maximum defluorination of PFDA of 49.89%, and PFHxA of 64.76% were obtained at 1 mL/min of flow rate due to increased exposure time to plasma generated reductive and oxidizing species. PFDA (C10), and PFHxA (C6) removal efficacy was enhanced by improving the surface activity by adding NaCl to increase conductivity between 0.25 mS/cm to 40 mS/cm. At 3 mS/cm, PFHxA showed 55.81% defluorination while C10 showed 40.85% at 25 mS/cm. The effect of different liquid phase scavengers such as ethanol for hydroxyl radicals and chloroacetate for aqueous electrons are studied. Scavenging both radicals and aqueous electrons decreased the defluorination rate of PFHxA by 48.31% while PFAD was reduced by only 3.84%. Overall, the results demonstrate high efficiency of PFAS degradation and mineralization, and thus indicates that the thin film gas liquid non-thermal plasma is a promising method for PFAS degradation.