Periodically reversing electrocoagulation technique for efficient removal of short-chain perfluoroalkyl substances from contaminated groundwater around a fluorochemical facility.

ABSTRACT

Widespread distributions of short-chain perfluoroalkyl substances (PFASs) has been recognized as a crucial environmental issue. However, multiple treatment techniques were ineffective due to their high polarity and mobility, contributing to a never-ending existence in the aquatic environment ubiquitously. The present study revealed potential technique of periodically reversing electrocoagulation (PREC) to perform efficient removal of short-chain PFASs including experimental factors (in the conditions of 9 V for voltage, 600 r/min of stirring speed, 10 s of reversing period, and 2 g/L of NaCl electrolyte), orthogonal experiments, actual application, and removal mechanism. Accordingly, based upon the orthogonal experiments, the removal efficiencies of perfluorobutane sulfonate (PFBS) in simulated solution could achieve 81.0% with the optimal parameters of Fe-Fe electrode materials, addition of 665 µL H2O2 per 10 min, and pH at 3.0. The PREC was further applied for treating the actual groundwater around a fluorochemical facility, consequently the removal efficiencies for typical short-chain perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), PFBS, and perfluoropentane sulfonate (PFPeS) were 62.5%, 89.0%, 96.4%, 90.0%, and 97.5%, respectively. The other long-chain PFASs contaminants had superior removal with the removal efficiencies up to 97%-100%. In addition, a comprehensive removal mechanism related to electric attraction adsorption for short-chain PFASs could be verified through the morphological analysis of ultimate flocs composition. The oxidation degradation was further revealed as the other removal mechanism by suspect and nontarget screening of intermediates formed in simulated solution, as well as density functional theory (DFT) calculation theory. Moreover, the degradation pathways about one CF2O molecule or CO2 eliminated with one C atom removed in PFBS by ·OH generated from the PREC oxidation process were further proposed. As a result, the PREC would be a promising technique for the efficient removal of short-chain PFASs from severely contaminated water bodies.