boron and perfluorooctanoic-acid

The removal of per- or polyfluorinated alkyl substances (PFAS) has received increasing attention because of their extreme stability, our increasing awareness of their toxicity at even low levels, and scientific challenges for traditional treatment methods such as separation by activated carbon or destruction by advanced oxidation processes. Here, we performed a direct and systematic comparison of two electrified approaches that have recently shown promise for effective degradation of PFAS: plasma and conventional electrochemical degradation. We tailored a reactor configuration where one of the electrodes could be a plasma or a boron-doped diamond (BDD) electrode and operated both electrodes galvanostatically by continuous direct current. We show that while both methods achieved near-complete degradation of PFAS, the plasma was only effective as the cathode, whereas the BDD was only effective as the anode. Compared to the BDD, plasma required more than an order of magnitude higher voltage but lower current to achieve similar degradation efficiency with more rapid degradation kinetics. All these factors considered, it was noted that plasma or BDD degradation resulted in similar energy efficiencies. The BDD electrode exhibited zero-order kinetics, and thus, PFAS degradation using the conventional electrochemical method was kinetically controlled. On the contrary, analysis using a film model indicated that the plasma degradation kinetics of PFAS using plasma were mass-transfer-controlled because of the fast reaction kinetics. With the help of a simple quantitative model that incorporates mass transport, interfacial reaction, and surface accumulation, we propose that the degradation reaction kinetically follows an Eley-Rideal-type mechanism for the plasma electrode, and an intrinsic rate constant of 2.89 × 10

Topics: Boron; Caprylates; Diamond; Electrodes; Fluorocarbons; Kinetics; Oxidation-Reduction; Water Pollutants, Chemical

This work deals with the electrochemical degradation and mineralization of perfluorooctanoic acid (PFOA). Model aqueous solutions of PFOA (100mg/L) were electro-oxidized under galvanostatic conditions in a flow-by undivided cell provided with a tungsten cathode and an anode formed by a commercial ultrananocrystalline boron doped diamond (BDD) coating on a niobium substrate. A systematic experimental study was conducted in order to analyze the influence of the following operation variables: (i) the supporting electrolyte, NaClO4 (1.4 and 8.4g/L) and Na2SO4 (5g/L); (ii) the applied current density, japp, in the range 50-200 A/m(2) and (iii) the hydrodynamic conditions, in terms of flowrate in the range 0.4×10(-4)-1.7×10(-4)m(3)/s and temperature in the range 293-313K. After 6h of treatment and at japp 200A/m(2), PFOA removal was higher than 93% and the mineralization ratio, obtained from the decrease of the total organic carbon (TOC) was 95%. The electrochemical generation of hydroxyl radicals in the supporting electrolyte was experimentally measured based on their reaction with dimethyl sulfoxide. The enhanced formation of hydroxyl radicals at higher japp was related to the faster kinetics of PFOA removal. The fitting of experimental data to the proposed kinetic model provided the first order rate constants of PFOA degradation, kc(1) that moved from 2.06×10(-4) to 15.58×10(-4)s(-1), when japp varied from 50 to 200A/m(2).

Topics: Boron; Caprylates; Diamond; Electrochemical Techniques; Electrodes; Electrolytes; Fluorocarbons; Hydroxyl Radical; Kinetics; Nanoparticles; Oxidation-Reduction; Water Pollutants, Chemical; Water Purification

The contribution of non-point sources to perfluorinated surfactants (PFSs) in a river was evaluated by estimating their fluxes and by using boron (B) as a tracer. The utility of PFSs/B as an indicator for evaluating the impact of non-point sources was demonstrated. River water samples were collected from the Iruma River, upstream of the intake of drinking water treatment plants in Tokyo, during dry weather and wet weather, and 13 PFSs, dissolved organic carbon (DOC), total nitrogen (TN), and B were analyzed. Perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS), perfluoroheptanoate (PFHpA), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), perfluorodecanoate (PFDA), perfluoroundecanoate (PFUA), and perfluorododecanoate (PFDoDA) were detected on all sampling dates. The concentrations and fluxes of perfluorocarboxylates (PFCAs, e.g. PFOA and PFNA) were higher during wet weather, but those of perfluoroalkyl sulfonates (PFASs, e.g. PFHxS and PFOS) were not. The wet/dry ratios of PFSs/B (ratios of PFSs/B during wet weather to those during dry weather) agreed well with those of PFS fluxes (ratios of PFS fluxes during wet weather to those during dry weather), indicating that PFSs/B is useful for evaluating the contribution from non-point sources to PFSs in rivers. The wet/dry ratios of PFOA and PFNA were higher than those of other PFSs, DOC, and TN, showing that non-point sources contributed greatly to PFOA and PFNA in the water. This is the first study to use B as a wastewater tracer to estimate the contribution of non-point sources to PFSs in a river.

Topics: Boron; Caprylates; Chromatography, High Pressure Liquid; Environmental Monitoring; Fluorocarbons; Rivers; Seasons; Sewage; Surface-Active Agents; Tandem Mass Spectrometry; Water Pollutants, Chemical