Defluorination of Aqueous Perfluorooctanesulfonate by Activated Persulfate Oxidation

<div><p>Activated persulfate oxidation technologies based on sulfate radicals were first evaluated for defluorination of aqueous perfluorooctanesulfonate (PFOS). The influences of catalytic method, time, pH and K₂S₂O₈ amounts on PFOS defluorination were investigated. The intermediate products during PFOS defluorination were detected by using LC/MS/MS. The results showed that the S₂O₈²⁻ had weak effect on the defluorination of PFOS, while the PFOS was oxidatively defluorinated by sulfate radicals in water. The defluorination efficiency of PFOS under various treatment was followed the order: HT (hydrothermal)/K₂S₂O₈ > UV (ultraviolet)/K₂S₂O₈ > Fe²⁺/K₂S₂O₈ > US (ultrasound)/K₂S₂O₈. Low pH was favorable for the PFOS defluorination with sulfate radicals. Increase in the amount of S₂O₈²⁻ had positive effect on PFOS defluorination. However, further increase in amounts of S₂O₈²⁻ caused insignificant improvement in PFOS defluorination due to elimination of sulfate radicals under high concentration of S₂O₈²⁻. CF₃(CF₂)_nCOOH (n = 0–6) were detected as intermediates during PFOS defluorination. Sulfate radicals oxidation and hydrolysis were the main mechanisms involved in defluorination process of PFOS.</p></div

Schematic representation of reactor. (A) UV/K₂S₂O₈. (B) US/K₂S₂O₈.

<p>Schematic representation of reactor. (A) UV/K₂S₂O₈. (B) US/K₂S₂O₈.</p

Possible defluorination pathways of PFOS in the activated K₂S₂O₈ oxidation systems.

<p>Possible defluorination pathways of PFOS in the activated K₂S₂O₈ oxidation systems.</p

Changes in the concentration of PFOS and intermediates through the PFOS defluorination in UV/K₂S₂O₈ system.

<p>Changes in the concentration of PFOS and intermediates through the PFOS defluorination in UV/K₂S₂O₈ system.</p

Mass spectrometry acquisition parameters of the intermediates. * Quantitative product ion.

<p>Mass spectrometry acquisition parameters of the intermediates. * Quantitative product ion.</p

Effect of K₂S₂O₈ amounts on defluorination of PFOS in activated K₂S₂O₈ oxidation systems.

<p>Effect of K₂S₂O₈ amounts on defluorination of PFOS in activated K₂S₂O₈ oxidation systems.</p

Time course of SO₄²⁻ amounts in activated K₂S₂O₈ oxidation systems.

<p>Time course of SO₄²⁻ amounts in activated K₂S₂O₈ oxidation systems.</p

The calculated pseudo-first-order constants and defluorination efficiency (%) of PFOS with 18.5 mM persulfate in activated K₂S₂O₈ oxidation systems at different initial pH values.

<p>The calculated pseudo-first-order constants and defluorination efficiency (%) of PFOS with 18.5 mM persulfate in activated K₂S₂O₈ oxidation systems at different initial pH values.</p

MRM spectra of assigned ionic compounds in the degraded solutions after 4h by UV/K₂S₂O₈ oxidation.

<p>MRM spectra of assigned ionic compounds in the degraded solutions after 4h by UV/K₂S₂O₈ oxidation.</p

Irradiation-time dependence of fluorine element mass balance during decomposition of PFOS in UV/K₂S₂O₈ systems.

<p>Irradiation-time dependence of fluorine element mass balance during decomposition of PFOS in UV/K₂S₂O₈ systems.</p