(402e) Investigation of Advanced Oxidation Processes for Removal of Perfluorooctanoic Acid (PFOA) from Aqueous Matrices

Perfluorooctanoic acid (PFOA) is a synthetic compound in the perfluoroalkyl substance (PFAS) family of chemicals. PFOA has been widely used in the production of Teflon, waterproof coatings, and many other industrial applications since the 1940s and has been identified as a human carcinogen by the United States Environmental Protection Agency (EPA). Agreements have been reached between major industrial users of this compound and the EPA to end the use of PFOA in the United States. This group of compounds is highly stable due to its chemical structure and does not easily biodegrade under natural conditions; thus, this persistent compound is found globally in ecosystems. The compound is also bioaccumulative. Current methods for removal of PFOA from water include reverse osmosis (RO) or adsorption, both of which concentrate the removed PFOA meaning that the concentrated material still needs to be handled and disposed of in a safe manner. Additionally, this removal is not particularly optimal. A majority of current research on removal of PFOA from aqueous matrices focuses on physical treatments including novel adsorbents.

Advanced oxidation processes (AOPs) are chemical oxidation processes that utilize hydroxyl radicals as the primary removal mechanism. They are classified as either dark or lighted AOPs. As the name suggests, dark AOPs do not utilize UV irradiation to catalyze formation of the hydroxyl radical from parent oxidizers while lighted AOPS utilize some form of UV irradiation to catalyze hydroxyl radical formation. Examples of dark AOPs include Fenton’s Reagent and peroxone, and examples of lighted AOPs include low- and medium-pressure ultraviolet lamps used in conjunction with hydrogen peroxide (LPUV + HP and MPUV + HP). These processes have a long history of successful use in treatment of water contaminated with organic pollutants that are difficult to treat with other processes. While the chemical structure of PFOA makes oxidation of the compound potentially difficult, research on the oxidation of PFOA using optimized AOPs shows promise. One major benefit of AOPs for removal of organic pollutants over methods that concentrate the pollutant is its destruction of the pollutant.

A 3L bench-scale oxidation reactor was used for all experiments with the PFOA concentration set at 500 µg/L and the PFOA analyzed using high performance liquid chromatography with tandem mass spectroscopy (HPLC-MS/MS). The lighted AOPs investigated utilized a low pressure Hg-vapor lamp, a 200 watt medium pressure Hg-vapor lamp, and a 450 watt medium pressure Hg-vapor lamp. For each medium pressure lamp, both hydrogen peroxide concentration and reactor temperature were varied independently. A novel optimization scheme of hydrogen peroxide dosing was evaluated for optimizing radical production from the H₂O₂ and managing radical scavenging also from the H₂O₂. Additionally, experiments using ozone as the primary oxidizer in the system have been conducted to determine the efficacy of ozone in removing PFOA.

The results showed promise for removal of PFOA via MPUV + HP suggesting that AOPs could be effective for removal of PFOA in contaminated waters under proper conditions. Optimizing H₂O₂ dosing proved useful and a method process designers should consider for removing refractory pollutants and reducing operational costs.