THE USE OF BORON-DOPED DIAMOND FILM ELECTRODES FOR THE OXIDATIVE DEGRADATION OF PERFLUOROOCTANE SULFONATE AND TRICHLOROETHYLENE

Abstract

The current treatment of water contaminated with organic compounds includes adsorption, air stripping, and advanced oxidation processes. These methods large quantities of water and require excessive energy and time. A novel treatment process of concentrating and then electrochemically oxidizing compound would be a more feasible practice. This research investigated the oxidative destruction of perfluorooctane sulfonate (PFOS), perfluorobutane sulfonate (PFBS) and trichloroethene (TCE) at boron-doped diamond film electrodes and the adsorption of PFOS and PFBS on granular activated carbon and ion exchange resins.Experiments measuring oxidation rates of PFOS and PFBS were performed over a range in current densities and temperatures using a rotating disk electrode (RDE) reactor and a parallel plate flow-through reactor. Oxidation of PFOS was rapid and yielded sulfate, fluoride, carbon dioxide and trace levels of trifluoroacetic acid. Oxidation of PFBS was slower than that of PFOS. A comparison of the experimentally measured apparent activation energy with those calculated using Density Functional Theory (DFT) studies indicated that the most likely rate-limiting step for PFOS and PFBS oxidation was direct electron transfer. The costs for treating PFOS and PFBS solutions were compared and showed that PFOS is cheaper to degrade than PFBS.Screening studies were performed to find a viable adsorbent or ion exchange resin for concentrating PFOS or PFBS. Granular activated carbon F400 (GAC-F400) and an ion exchange resin, Amberlite IRA-458, were the best methods for adsorbing PFOS. Ionic strength experiments showed that the solubility of the compounds affected the adsorption onto solid phases. Regeneration experiments were carried out to determine the best method of recovering these compounds from the adsorbents; however, the compounds could not be effectively removed from the adsorbents using standard techniques.The electrochemical oxidation of trichloroethene (TCE) at boron-doped diamond film electrodes was studied to determine if this would be a viable degradation method for chlorinated solvents. Flow-through experiments were performed and showed TCE oxidation to be very rapid. Comparing the data from the DFT studies and the experimentally calculated apparent activation energies the mechanism for TCE oxidation was determined to be controlled by both direct electron transfer and oxidation via hydroxyl radicals.