Degradation of perfluorooctane sulfonatevia in situelectro-generated ferrate and permanganate oxidants in NOM-rich source waters

Sean T Mcbeath,Nigel J D Graham

doi:10.1039/d1ew00399b

Abstract

The electrooxidation of PFOS can be significantly improved with the simultaneous electrosynthesis of ferrate and permanganate from low concentration ambient Fe2+and Mn2+in source waters, even in the presence of natural organic matter (NOM).

Highlights

Per- and polyfluoroalkyl substances (PFAS) are a wide class of synthetically made chemicals, characterised by an aliphatic carbon backbone with fluorine atom substitutions on the alkyl chain in place of hydrogen
The same initial Mn2+ concentrations (182 and 55 μM) and Fe2+ concentrations (54, 18 and 9 μM), at three current density conditions of 10, 40 and 80 mA cm−2 over 120 minutes of electrolysis, were used for the Perfluorooctane sulfonate (PFOS) degradation experiments; an additional Fe2+ initial concentration of 179 μM was investigated. For both ferrate and permanganate synthesis processes, the operating cell potentials were relatively stable throughout the entirety of electrolysis (120 minutes), regardless of the initial iron or manganese concentration, but were dependent on the current density: 6.0–6.6 V, 14.1–14.7 and 18.0–18.6 V during 10, 40 and 80 mA cm−2 operations
It was previously observed that no significant differences in ferrate synthesis were observed during electrolysis at the three current density conditions, despite increased generation ofOH as the current density increased, as described elsewhere.[38,40]

Summary

Introduction

Per- and polyfluoroalkyl substances (PFAS) are a wide class of synthetically made chemicals, characterised by an aliphatic carbon backbone with fluorine atom substitutions on the alkyl chain in place of hydrogen. Perfluorooctane sulfonate (PFOS) is a ubiquitous PFAS species, consisting of an eight carbon chain and hydrophilic sulfonate functional group, previously used in a number of applications including as a mist suppressant agent for carcinogenic aerosols,[1] aqueous film-forming foams, surfactants and lubricants,[2] as well as various household. Environmental Protection Agency (US EPA) survey found PFOS contamination ranging from 40–43 ng L−1 as an average in 50 US states in contaminated waters, with individual levels ranging from trace to over 1800 ng L−1.7 Other studies have found PFOS at concentrations of 132 ng L−1 in US surface waters,[8] and as high as 0.011–2270 μg L−1 in waters near the release of aqueous film fire-fighting foam..

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Conclusion