Authors:
Fernando Pardo | Universidad Complutense de Madrid | Spain
Virginia Huerta | Universidad Complutense de Madrid | Spain
Prof. Esperanza Montero | Universidad Complutense de Madrid | Spain
Dr. Sergio Rodríguez | University Complutense of Madrid | Spain
PhD Aurora Santos | University Complutense of Madrid. CIF Q-2818014-I | Spain
Prof. Arturo Romero | University Complutense of Madrid | Spain
INTRODUCTION
Perfluorooctanoic acid (PFOA), as a compound of the group of PFCAs (perfluorocarboxilic acids), and perfluorooctane sulfonate (PFOS), have been widely used in industry, such as surfactants, surface treatment agents, polymers, metal coating, fire retardants, etc. during the last decades. Due to their hydrophobic and oleophobic nature, and chemical and thermal resistance, PFOA and PFOS tend to bioaccumulate and resist degradation (meeting the “persistent” and “very persistent” EU criteria) [1].
Although PFOA and PFOS have been prohibited from industrial uses, they still remain in the environment, resulting in serious health and ecological risks due to their proven toxicity and likely carcinogenic effects, furthermore, there have been several cases reporting the presence of PFOA and PFOS in some tissues and organs of both humans and animals. Therefore, the need to remove this kind of contaminants from the environment has been considered as a matter of increasing interest in the last years [1], [2].
Because of the strong fluorine-carbon bond and low vapor pressure, conventional treatment technologies such as bioremediation and direct oxidation have not offered satisfactory removal efficiencies. Whilst, on the other hand, activated carbon filters and reverse osmosis have shown effectiveness for the abatement of PFCs in water until acceptable levels, although for complete destruction of PFOS and PFOA it is necessary to incinerate the concentrated waste. Therefore, the current solutions for the removal of these pollutants are questioned in regards to their cost-effectiveness. [1]
Due to this fact, alternative technologies have been studied, such as photochemical oxidation, thermally-induced reduction, sonochemical degradation and persulfate oxidation. In case of chemical oxidation, it would be necessary to study different reaction conditions, regarding persulfate and hydrogen peroxide activation for hydroxyl radical production, in order to assess the extent of the effectiveness of all these oxidation techniques. [3], [4].
In this work it has been studied the use of activated persulfate by different ways and Fenton reagent for the removal of PFOA and PFOS, it has been also studied the defluorination grade in order to ensure a complete degradation of the pollutant.
EXPERIMENTAL
Water samples contaminated with PFOA and PFOS 0.1 mM each, were treated with Fenton Reagent and activated persulfate. Both advanced oxidation techniques were carried out by modifying the type of activator. In case of Fenton reagent, activation was carried out by adding only ferric sulfate and ferric sulfate combined with humic acids. For persulfate activation, it was used temperature (ranging from 25 to 70 ºC), zerovalent iron, alkaline conditions (pH=12) and persulfate combined with ferric sulfate and humic acids.
Reactions, carried out in glass reactors covered with aluminum foil in order to avoid sunlight, were performed at 25 ºC by orbital shaking, while for those corresponding to higher temperatures (>25 ºC), a glicerine bath with magnetic stirring was used. Concentration of contaminants, pH, fluoride in solution and remaining oxidant were followed during reactions.
PFOA was analyzed by HPLC with a Diode Array Detector (maximum absorbance 190 nm), fluoride was followed by a selective electrode in order to study the defluorination grade. Hydrogen peroxide was measured by potentiometric titration with KMnO4 and persulfate by indirect potentiometric titration of iodide (KI) with sodium thiosulfate. A glass electrode was used for pH measurement.
RESULTS
Higher removal efficiencies of PFOA were obtained with activated persulfate by temperature, zerovalent iron and ferric sulfate with humic acids. Regarding Fenton reagent, the best result was obtained when ferric salt and humic acids were used.
In terms of defluorination, persulfate activation with temperature offered the highest efficiencies for both PFOA and PFOS, while for other techniques, despite the high removal efficiencies of contaminant, incomplete defluorination rates were obtained.
REFERENCES
[1] Environmental protection agency (USA). Emerging Contaminants – Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA).
[2] Lee et al. Persulfate oxidation of perfluorooctanoic acid under the temperatures of 20–40°. Chemical Engineering Journal. Volumes 198–199, 1 August 2012, Pages 27–32.
[3] Wang et al. Electrochemically enhanced adsorption of PFOA and PFOS on multiwalled carbon nanotubes in continuous flow mode. Chinese Science Bulletin. August 2014, Volume 59, Issue 23, pp 2890-2897
[4] Yang et al. Oxidative Degradation of PFOA/PFOS with Physicochemical Techniques. PROGRESS IN CHEMISTRY. Volume 26, 7 Pages: 1265-1274.
ACKNOWLEDGEMENTS
The authors acknowledge financial support from the Comunidad Autonoma de Madrid provided throughout projects CARESOIL (S2013-MAE-2739) and from Spanish Ministry of Science and Innovation, projects CTM2010-16693 and CTM2013-43794-R.