Adsorption Behavior and Fate of Perfluorochemicals (PFCs) Discharged from Municipal Wastewater Sludge

Abstract

The global distribution, persistence nature, and strong bioaccumulation have initiated our strong concern about the adsorption behavior and fate of perfluorochemicals (PFCs). This study will first report our findings on the discharge characteristics of PFCs from wastewater sludge generated from a typical urban environment. Then, the results of adsorption experiments for selected PFC compounds on different alumina adsorbents will be introduced as an example of our new understandings on the adsorption behavior of PFCs. In the case of observing the adsorption behavior of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) on boehmite, a common form of hydrated aluminum oxide existing in soils and sediments, this result clearly indicated the influence of solution chemistry in the adsorption behavior. Kinetic experiments show that the adsorption equilibrium can be achieved within 48 hours and the boehmite surface is generally receptive to PFOS and PFOA adsorption. The adsorption isotherms estimated the maximum adsorption capacities of PFOS and PFOA on boehmite to be 0.877 µg/m2 and 0.633 µg/m2, respectively. The increase of pH can lead to a moderate decrease of PFOS and PFOA adsorption, owing to the increase of ligand exchange reaction and the decrease of electrostatic interaction. With the compression of electrical double layers, the competitive adsorption from the other ions and the calcium ion bridging effect between perfluorochemicals have demonstrated their negative influence for PFOS and PFOA adsorption on boehmite surface. In this study, the humic acid (HA) also showed significant retardant effects on the sorption of PFOS and perfluorobutanesulfonate (PFBuS) on boehmite. Finally, this study will briefly show the result of how the thermal treatment of lime-conditioned sludge may affect the fluorine transport in PFOS compound as an example of demonstrating the influence of modern urban sludge treatment method on the fate of emerging contaminants.