Degradation mechanism of perfluorooctanoic acid (PFOA) during electrocoagulation using Fe electrode

Abstract

In this study, the electrocoagulation of perfluorooctanoic acid (PFOA) in water using an iron (Fe) electrode was investigated. The effects of the current density, stirring speed, and electrolyte concentration (NaCl) on the corresponding removal rates of PFOA were examined. An increase in the current density from 2.4 to 80.0 mA cm−2 led to a significant increase in the removal efficiency of PFOA from 10.0 to 100.0% within 6 h. Formate (HCOO−) ions and three shorter-chain perfluorocarboxylates (i.e., perfluoropentanoic acid; PFPeA, perfluorohexanoic acid; PFHxA, and perfluoroheptanoic acid; PFHpA) were observed as organic byproducts during the electrocoagulation of PFOA, indicating that the C-C bond between C7F15 was first broken down and then was degraded into short carbon-chain compounds by PFOA decomposition. 65% of fluorine recovery as fluoride ions and organic fluorine in shorter-chain byproducts (PFPeA, PFHxA, and PFHpA) with 60% of total organic carbon (TOC) removal was achieved within 6 h during electrocoagulation, while the complete removal of PFOA was achieved. Our results imply that electrocoagulation using Fe electrode can effectively degrade PFOA into shorter-chain byproducts with significant mineralization.