Removal of poly- and perfluoroalkyl substances from water using the BDD electrode

Abstract: Poly-and perfluoroalkyl substances (PFASs) have been used for a wide range of purposes due to their unique properties. Unfortunately, these compounds have been associated with several adverse health effects and high persistence in the environment, therefore, creating a need for their elimination from the environment. In this study, electrochemical oxidation using boron-doped diamond electrodes (BDD) was tested for its treatment efficiency of 12 PFAS. Three different water types were used that is: Millipore, dissolved organic carbon (DOC) and membrane reject water. Both Millipore and DOC water were spiked and tested with three different current densities that is: 0.95 mA cm-2, 4.8 mA cm-2 and 12 mA cm-2. Quality assurance tests on the electrode revealed that the electrode was consistently efficient throughout the study and that pH change influenced PFAS removal. In this study, 12 mA cm-2, proved to be the most efficient tested current density achieving > 80% removal for PFASs except perfluorohexane carboxylate (PFHxA) (79%) and perfluorobutane carboxylate (PFBS) (34%) after two hours. At all current densities used, perfluoropentane carbxylate (PFPeA), a compound that was not spiked, was observed to have been formed in differentgmnneyney quantities. In majority of the trials, PFAS removal was dependent on perfluorocarbon chain length and was found to increase with increase in perfluorocarbon chain length. The effect of water type on PFAS removal was dependent on the PFAS type. For example, while PFBS removal was enhanced in DOC water, for most of the compounds it was decreased. PFAS removal from membrane reject water was greater than that from DOC water except for PFHxA. In this study, short chained carboxylates had lower removals. This could be due to the treatment pathway undertaken by the BDD. This study examines factors that should be examined to transfer the treatment from a laboratory scale to water treatment plants. Further studies may examine wider ranges of water types as well as provide an account of all the products produced during water treatment.