Non-Thermal Plasma Bubble Columns for PFAS Remediation

Abstract

A hybrid non-thermal plasma bubble column has been successfully developed for the destruction of PFAS in aqueous solutions at working volumes from 2 L up to 25 L. Controlled studies to investigate the breakdown behaviour of perfluorocarboxylic acids (PFCA) and perfluorosulfonic acids (PFSA), containing 4-10 carbon atoms has determined a compound’s treatability by the developed reactor correlates with the length of its backbone, with compounds possessing longer perfluorinated carbon chains exhibiting a greater degree of treatability. Inorganic fluoride ions were identified as the dominant breakdown product in the liquid phase, accounting for 40-60% of the total fluorine present in the PFAS starting material, in addition to a range of sequentially shorter chain daughter PFAS which accounted for only <5% of the total fluorine. Increasing the scale of the treatment reactor from 2 L to 5 L and 25 L was found to improve breakdown rates and reduce the energy requirements to remove 90% of a contaminant, perfluorosulfonate (PFOS), in a normalised 1 m3 volume of water from 6.5 kWh/m3, to 3.1 kWh/m3 to 1.6±0.1 kWh/m3. The overall PFAS breakdown rate was determined to be limited by the transport of species on the surface of the rising bubbles for destruction at the liquid surface, which could be maximised by using fine bubbles <1.0 mm in diameter with high surface area-to-volume ratios. The work has contributed to understanding the applicability of utilising non-thermal plasma discharges for destroying PFAS in liquid and demonstrated potential improvements in treatment efficiency when treating larger volumes of liquid. This work has also shown the potential scalability of this treatment reactor to meet the needs of remediating contaminated sites in real-world applications.