Application of ionizing radiation in decomposition of perfluorooctanoate (PFOA) in waters

Abstract

It has been demonstrated through the use of both gamma-rays and beam of accelerated electrons (EB) for the radiolytic decomposition of PFOA in diluted aqueous solutions that the most reactive species among the products of water radiolysis are hydrated electrons eaq. The reaction of PFOA with the hydrated electrons takes place with the largest yield in strongly alkaline deaerated solutions.The PFOA decomposition performed at an initial concentration level of 1 mg/L by γ-irradiation requires the use of absorbed doses below 10 kGy, which, depending on the activity of employed 60Co source, requires 2–3 h irradiation time. Similar results were obtained at pH 12 in the presence and also in the absence of t-butanol in the treated solutions. In the case of EB irradiation in a wide range of the absorbed doses (up to 100 kGy), a very pronounced effect of the dose-rate was observed, which can be attributed to various recombination reactions of the products of water radiolysis. A significant improvement in the yield of the PFOA decomposition by EB irradiation can be observed in the presence of trace amounts of nitrate or 100 mM of a formate in the treated solutions. In optimized conditions, about 70–80% decomposition of the initial level of 1 ppm of PFOA can be obtained with an irradiation using 100 kGy absorbed dose, which corresponds to about 5 s treatment with the use of an employed electron accelerator. The acute toxicity measurements and a kinetic modeling are presented, together with a suggestion of the mechanism of radiolytic decomposition of PFOA.