Experimental investigations of Per- and Poly-fluoroalkyl substances (PFAS) degradation by non-thermal plasma in aqueous solutions

Abstract

The treatability of perfluorocarboxylic acids (PFCA) (perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA)) and perfluorosulfonic acids (PFSA) (PFBS, Perfluorooctanesulfonic acid PFHxS and Perfluorooctanesulfonic acid (PFOS)) via a bubble column with non-thermal plasma discharges in the argon headspace were investigated in individual solutions and from surface water sourced from a contaminated site. High degradation (>90%) could be achieved for PFOA, PFHxS and PFOS within 40 min treating the contaminated surface water. Overall, treatability correlated with the length of the perfluorinated carbon chain, with a decrease in treatability associated with a reduction of the length of the perfluorinated backbone. Experiments with prepared PFAS solutions at initial concentrations of 10, 25 and 50 μg/L found higher initial concentrations of PFCA and PFSA were associated with faster degradation rates suggesting the treatment efficiency was limited by mass transfer of PFAS. Negligible breakdown was observed for PFBA at any of the concentrations trialled, indicating limitations when treating more hydrophilic PFAS, which may require combining this treatment approach with a polishing step, such as nanofiltration.