Removal of typical perfluorinated surfactants from water using some conventional adsorbents

摘要

Perfluorinated surfactants such as Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) have increasingly attracted global concerns in recent years due to their global distribution, persistence, strong bioaccumulation and potential toxicity. They had been detected in wastewater, surface water, groundwater and even tap water throughout the world. In 2009, PFOS has been listed as one of persistent organic pollutants in COP4. As industrial wastewater has been implicated as a point source for PFOS and PFOA entering into natural waters, source control of PFOS and PFOA release into water environment becomes crucial. Some conventional techniques including biological degradation, oxidation and reduction are difficult to destruct PFOS and PFOA in ambient environments due to their stable properties, while adsorption would be an effective technique to remove them from aqueous solution. In this study, the feasibility of using powder activated carbon (PAC), granular activated carbon (GAC) and different resins to remove PFOS and PFOA from water was investigated. The sorption behaviors including sorption kinetics, isotherms, effect of solution pH and temperature were studied in detail, and the possible sorption mechanisms were discussed. In the sorption kinetics, it was found that the adsorption of PFOS and PFOA on the GAC very slow and the sorption equilibrium was achieved after at least 168 h, while the sorption equilibrium time was only about 4 h using the PAC, indicating that the adsorbent size significantly affected the sorption velocity of PFOS and PFOA. In contrast, the sorption kinetic of PFOS and PFOA on the resins was dependent on their matrix and functional groups. The resin matrix had significant impact on the sorption kinetic. The adsorption of PFOS on the polystyrene divinylbenzene based anion exchange resins such as AI400 was very slow and the sorption equilibrium was not obtained after 10 days, which was due to the strong hydrophobic property of the matrix and the difficult diffusion of PFOS molecules into the intraparticle pores. When the polyacrylic ester based anion exchange resins such as IRA67 were used to remove PFOS, the sorption equilibrium was achieved after 48 h, while the sorption equilibrium on the nonionic resin XAD7 was reached after 24 h. The functional groups including quaternary ammonium and polyamine on the resins were favorable for PFOS removal. The resin pores had little effect on the sorption kinetic of PFOS. The sorption kinetics of PFOS and PFOA on the activated carbon and resins can be described well using the pseudo-second-order and Elovich equation, and the intraparticle diffusion model can well fit their sorption on the GAC and AI400 in the initial stage.