Experimental investigation on the perfluorooctanoic and perfluorooctane sulfonic acids fate and behaviour in the activated sludge reactor

Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are the most investigated compounds in the class of perfluoroalkyl substances for their persistence and wider diffusion in the environment. However, fate and behaviour of PFOA and PFOS in the Wastewater Treatment Plants (WWTPs) have not been fully understood yet. The aim of the present study was to obtain a better understanding of the processes occurring to PFOS and PFOA in the activated sludge reactor. Several experimental tests were performed in the presence of activated sludge and sterilized sludge. PFOA and PFOS showed removals from the liquid phase from 59% to 68% and from 66% to 96%, respectively, for initial concentrations from 200 ng/L to 4000 ng/L in the presence of activated sludge. A significant fraction of the initial contaminant load was found adsorbed on the sludge, mainly in the case of PFOS. Other processes occurred, not fully identified, which were responsible of a further loss from the system. Leaching tests showed negligible release of the adsorbed pollutants from the sludge. Carbon and ammonia removal in the activated sludge reactor were not significantly affected by the presence of PFOA and PFOS. The pseudo-second order kinetic model and the Freundlich isotherm provided the best fitting of the experimental data.