Efficient electrochemical degradation of poly- and perfluoroalkyl substances (PFASs) from the effluents of an industrial wastewater treatment plant

Abstract

This paper reports the electrochemical treatment of poly-and perfluoroalkyl substances (PFASs) in the effluent from an industrial wastewater treatment plant (WWTP). While most of the previous research focused on the electrochemical degradation of perfluorooctanoic acid and perfluorooctane sulfonate in model solutions, this work studies the simultaneous removal of 8 PFASs at environmentally relevant concentrations in real industrial emissions, which also contained organic matter and inorganic anions. The overall PFASs content in the WWTP effluent was 1652 µg/L, which emphasized the need to develop innovative technologies for the management of PFASs emissions. 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) and 6:2 fluorotelomer sulfonate (6:2 FTSA) were the major contributors (92% w/w) to the overall PFASs content, that also contained significant amounts of short-chain perfluorocarboxylic acids (PFCAs). Using a boron doped diamond (BDD) anode of 0.0070 m 2 , the effluent (2 L) was treated by applying a current density of 50 mA/cm 2 for 10 hours, that resulted in 99.7% PFASs removal. The operation at lower current densities (5 and 10 mA/cm 2 ) evidenced the initial degradation of 6:2 fluorotelomers into perfluoroheptanoic and perfluorohexanoic acids, that were later degraded into shorter chain PFCAs. The high TOC removal, >90%, and the fluoride release revealed that PFASs mineralization was effective. These results highlight the potential of the electrochemical technology for the treatment of PFASs contained in industrial wastewaters, which nowadays stands as the main source of this group of persistent pollutants into the environment.

Water Treatment Technologies for PFAS: The Next Generation

“…Changes in inorganic chlorine species chloride (Cl‐), free chlorine (Cl2), chlorate (ClO3 ‐), and perchlorate (ClO4 ‐) over 10 h of electrochemical treatment at 50 milliAmps per centimeter squared (mA/cm 2 ) in typical wastewater treatment effluent. Results are averages of duplicate data, and suggest a nearly 1:4 ratio of influence Cl‐ (1341.4 mg/L) to effluent ClO4 (4070.3 mg/L) (modified from Gomez‐Ruiz et al ).…”

“…Electrochemical treatment refers to direct electron transfer from an anode to a molecule within an electrochemical cell designed with an anode, cathode, and electrolyte. Electrochemical cells can be divided or undivided, have demonstrated effectiveness for PFOA/PFOS at current densities of 1 to 50 mA/cm 2 , and use various custom‐synthesized mixed metal oxide anodes (Schaefer et al ; Urtiaga et al ; Gomez‐Ruiz et al ; Schaefer et al ). The materials of construction of an anode can have a meaningful influence on electrochemical treatment performance because the PFAS interaction at the surface of the anode constitutes the destructive mechanism.…”

“…Thus, while evidence has been reported throughout the literature recently on the potential for electrochemical treatment, this form of PFAS water treatment is under development. For example, the effectiveness of electrochemical treatment to mineralize long‐chain PFAA requires further study as over typical residence times of 4 to 10 h the persistent generation of short‐chain PFAA has been observed (Gomez‐Ruiz et al ). Further, as demonstrated in Figure , greater than 4000 mg per liter perchlorate was generated after 10 h of electrochemical treatment (Gomez‐Ruiz et al ).…”

“…For example, the effectiveness of electrochemical treatment to mineralize long‐chain PFAA requires further study as over typical residence times of 4 to 10 h the persistent generation of short‐chain PFAA has been observed (Gomez‐Ruiz et al ). Further, as demonstrated in Figure , greater than 4000 mg per liter perchlorate was generated after 10 h of electrochemical treatment (Gomez‐Ruiz et al ). The production of toxic by‐products (e.g., hydrogen fluoride, chlorine gas, bromate, perchlorate, and adsorbable organic halides) have been reported and may form when treating PFAS‐contaminated wastewater with cocontaminants via electrochemical treatment (Trautmann et al ).…”

Current to Clean Water – Electrochemical Solutions for Groundwater, Water, and Wastewater Treatment

“…Typically, the organic fraction of wastewaters is displayed by the chemical oxygen demand (COD) and/or the total organic carbon (TOC) , . A classification of compounds that contribute to COD was given by Moreno‐Casillas et al ; besides others, they classified the organic compounds into suspended solids, e.g., colloids, micelle liquids, e.g., alcohols, and dissolved solids and liquids, e.g., sugars.…”