Effectiveness of Non-Thermal Plasma Induced Degradation of Per- and Polyfluoroalkyl Substances from Water

Abstract

Per- and polyfluoroalkyl substances (PFAS) are omnipresent synthetic chemicals. Due to their industrial importance and widespread use as a key component in various applications and a variety of products, these compounds can be found today in high concentrations (>1 μg/L) in surface and groundwater but also spread throughout the ecosystem, where they represent a serious threat to most living organisms. The removal or degradation of PFAS contaminants from water and soil is becoming a legal obligation in a growing number of countries around the globe. This, however, demands novel techniques for the degradation of PFAS since conventional water treatment techniques are either insufficient or extremely expensive due to the persistent nature of these compounds caused by their extraordinary chemical stability. The goal of this work was therefore to investigate the practical potential of the application-oriented use of atmospheric non-thermal plasma as a powerful advanced oxidation method for the purification of water contaminated with PFAS compounds. Special attention was devoted to the development of the concept that can be scaled up to the capacity level of approximately 100–200 m3 of water per hour, contaminated with PFAS and other contaminants including organic and inorganic material generally present in soil, and surface or groundwater. Our major research interest was to define the minimum required treatment time for optimal purification results, as well as to understand the influence of the initial concentration of PFAS in water and the potential presence of co-contaminants often present in situ on the efficiency of the degradation process. A chemical analysis of the treated samples demonstrated the ability of the atmospheric plasma to reduce more than 50% of the initial PFAS amount in the water samples in less than 300 s of treatment time. PFOA, however, showed more rigidity towards degradation, where a double treatment time was needed to reach similar degradation levels. The obtained results showed that the initial concentration level does not play a major role in the process. However, the PFAS degradation profiles for all tested concentrations show a strongly nonlinear behavior with time, characterized by the fast decrease of the process efficiency in the case of longer treatment times. For prolonged treatment times, a constant increase in the samples’ conductivity was measured, which might be the limiting factor for the degradation rate in the case of prolonged treatment times.

Effects of Non-Thermal Plasma on the Transition from Nano-Crystalline to Amorphous Structure in Water and Subsequent Effects on Viscosity

“…The non-equilibrium nature of non-thermal plasma can produce very high concentrations of chemically active species while keeping bulk temperatures as low as room temperature. These characteristics aid its use in material processing, for pollutant treatments, in biomedical applications, medicine, space craft sterilization, hydrogen sulfide mitigation, PFAS mitigation, agricultural applications, and beyond [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

An Energy Efficient Process for Degrading Perfluorooctanoic Acid (PFOA) Using Strip Fountain Dielectric Barrier Discharge Plasma

“…Perfluorooctanoic acid (PFOA) is a type of artificially synthesized per-fluorinated compound (PFC) [1]. The C-F bond in the molecule has a large bond energy (485 kJ/mol), which makes PFOA a chemical with excellent thermal stability, chemical stability, surface inactivity, and high hydrophobicity [2][3][4]. Therefore, PFOA is commonly used as a surfactant in the industry to produce firefighting coating, soap, shampoo, etc.…”

Mechanism and Reactive Species in a Fountain-Strip DBD Plasma for Degrading Perfluorooctanoic Acid (PFOA)

“…Perfluorooctanoic acid (PFOA) is an artificially synthesized, highly stable perfluorinated compound (PFC) [1,2], which is commonly used as a surfactant in industries to produce firefighting coating, soap, shampoo [3,4], etc. It does not degrade naturally [5,6] and is highly persistent in the environment [7], which can cause potential harm to the ecological system [8].…”