The Rejection of Pharmaceutically Active and Endocrine Disrupting Compounds via Nanofiltration as a Function of Natural Water Components

This research investigated the rejection of seventeen pharmaceutically active (PhACs) and endocrine disrupting compounds (EDCs), representing a wide range of physicochemical properties, via nanofiltration (NF) from laboratory-prepared as well as raw and pre-treated surface waters (Lake Ontario and Otonabee River waters). The overall objective was to examine the rejection of PhACs and EDCs as a function of compound interactions with naturally occurring organic matter fractions, colloidal particles, and cations via nanofiltration. The specific PhAC/EDCs preferentially interacting with water constituents, and significant physicochemical properties influencing NF rejection were identified. In laboratory-prepared controls (Milli Q), PhAC/EDC rejection increased with increasing MW and molecular volume; however rejection decreased with increasing Log D. Naturally occurring dissolved organic matter (DOM) fractions were found to interact preferentially with neutral PhAC/EDCs, resulting in increased rejection due to enhanced size exclusion of compound-humic substance (HS) pseudo-complexes arising from dipole-dipole interactions. Increased cation concentration decreased removal of neutral compounds by decreasing the availability of HS interaction sites. The rejection of specific ionic PhAC/EDCs was influenced by both size and charge effects of the compound-HS complexes. Increased compound rejection, however, could not be linearly related to higher concentrations of humic substances in the source waters. The presence of natural colloidal and suspended particles resulted in a significant decrease in the rejection of most neutral PhAC/EDCs, attributable to enhanced hydrophobic interactions (solute partitioning) at the membrane surface.Natural water matrix components interacted preferentially with neutral PhAC/EDCs when compared to ionic PhAC/EDCs. Overall, neutral compounds were most effectively rejected by NF in ultrafiltration (UF)-pretreated water (colloids removed), while rejection was consistently lowest in the fluidized ion exchange (FIEX)-pretreated water (DOM removed) with increased cation concentrations. An increase in cation concentration caused significant decreases in rejection in the absence of colloidal particles, suggesting that colloids provide some cation-buffering capacity and minimize the impact of cations on rejection.Ph.D