Perfluoroalkyl Chemical Adsorption by Granular Activated Carbon: Impacts of Source Water Characteristics

Water characteristic impacts on granular activated carbon (Filtrasorb 400) adsorption of nine per- and polyfluoroalkyl substances (PFAS) were studied. Multispecies competitive isotherms had lower effective solid phase capacities (q _e ) than single species isotherms. pH 9 q _e s were somewhat reduced (max 19%) compared to pH 7.7-8.1. Decreasing ionic strength (10 to 2 mM) substantially (79%-146%) increased PFAS q _e s. Divalent ion (calcium and sulfate) presence without changing ionic strength increased q _e s (43%-140%). Natural organic matter (NOM) presence reduced PFAS q _e s with the reduction somewhat offset by calcium and sulfate presence. This reduced capacity suggested both direct competition with NOM and pore-blockage hindered PFAS adsorption. Ideal adsorbed solution theory poorly predicted the competition, likely due to nonideal behaviors of adsorbed species and GAC surface heterogeneity. Findings provide insights into the complex interactions between different water constituents and the adsorptive surface to help optimize PFAS treatment efficacy and minimize operational costs.