No abstract

“High-concentration” and “low-concentration” bench-scale batch plasma reactors were used to effectively degrade per- and polyfluoroalkyl substances (PFAS) at a high concentration (∼100 mg/L) and a low concentration (<1 μg/L), respectively, in ion exchange (IX) regenerant still bottom (SB) solutions. In the SBs, numerous PFAS were detected with a wide concentration range (∼0.01 to 100 mg/L; total oxidizable precursors (TOP) ∼4000 to 10000 mg/L). In the “high-concentration” plasma reactor, the concentrations of PFAS precursors and long-chain perfluoroalkyl acids (PFAAs) (≥6C for PFSAs and ≥8C for perfluorocarboxylic acids (PFCAs)) were decreased by >99.9% in 2 h, and short-chain PFAAs (<6C for perfluorocarboxylic acids (PFSAs) and <8C PFCAs) were decreased by >99% in 6 h of treatment. Subsequently, a “low concentration” plasma reactor was used to remove additional PFAAs. In this reactor, the addition of CTAB (cetrimonium bromide, a cationic surfactant) caused short-chain PFAAs, other than PFBA, to be removed to below detection limits in 90 min of treatment time. Overall, >99% of the TOP present in SBs was removed during the treatment. Fluorine recovery of 47 to 117% was obtained in six SB samples. Energy requirement (EE/O) for the treatment of PFOA and PFOS from SBs ranged from 380 to 830 kWh/m3.

A novel electron beam irradiation process has proven to be effective in removing thioanisole (methyl phenyl sulfide, CH3S−C6H5) from aqueous solutions. This paper presents substrate destruction data at pH 5 and pH 9. To apply a kinetic model, which predicts removal efficiencies, overall rate constants for reactions of thioanisole with •OH radicals, hydrated electrons, and hydrogen atoms were newly measured or carefully re-determined by pulse radiolysis. The respective values are (9.90 ± 0.13) × 109, (3.1 ± 0.1) × 108, and (3.24 ± 0.08) × 109 (M s)-1. Comparison of the model predictions to the experimental results revealed a very good agreement at pH 5 and an overestimation of the removal at pH 9. The presence of an additional scavenger at pH 9 but not at pH 5 reacting with •OH radicals, hydrated electrons and hydrogen atoms is considered to be responsible for the decrease in removal efficiency.