Factors Influencing the Ferric Ion-mediated Photochemical Decomposition of Perfluorooctane Sulfonate (PFOS) in Water

Perfluorooctane sulfonate (PFOS) has received increasing attention due to its persistence in the environment, accumulation and global occurrence. The enhancement of the photochemical oxidative degradation of perfluorooctane sulfonate upon addition of ferric ions under 254-nm UV and 185-nm vacuum UV (VUV) light was observed for the first time. In the presence of ferric ions (100 mu M) and at pH 3.0, 85.3% of the initial PFOS (20 mu M) was decomposed, with the rate constant of 1.92 d(-1), and the defluorination ratio reached 47.5% within 24 h under 254-nm UV irradiation. The influences of the ferric ion concentration, the solution pH and the UV wavelength on the PFOS photodecomposition were investigated. In addition, the photochemical decomposition of PFOS in the secondary effluent from a municipal wastewater plant was investigated. The coexisting organic matter in the secondary effluent greatly reduced the PFOS decomposition rate to less than 1/3 of that in pure water under 254-nm UV irradiation. However, under 185-nm VUV light the coexisting organic matter could be quickly degraded, and accordingly their adverse impacts could be largely eliminated. Moreover, the influences of initial PFOS concentration in the secondary effluent was examined under UV254 or UV254+185 light in the presence of ferric ions (100 mu M), PFOS at a lower concentration (2 mu M) decomposed much faster than that at a higher concentration (20 mu M), and its decomposition intermediates, i.e., C2-C7 perfluorinated carboxylic acids, could also be decomposed and mineralized.