Impact of natural water colloids and cations on the rejection of pharmaceutically active and endocrine disrupting compounds by nanofiltration

Abstract

The rejection of pharmaceutically active (PhACs) and endocrine disrupting compounds (EDCs) via a nanofiltration (NF) membrane was investigated as a function of naturally occurring colloidal and suspended particles, and cations. NF rejection of PhAC/EDCs was evaluated using a surface water that had been pre-treated by fluidized ion exchange (FIEX) to remove the humic fraction of dissolved organic matter yet retain the colloidal particles, and FIEX-pretreated water with cations added (Ca2+, Mg2+, Na+). 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. The rejection of ionic compounds was governed by electrostatic interactions with the membrane surface and was not significantly affected by the presence of colloidal particles. The addition of cations to FIEX-pretreated water did not generally impact rejection of most compounds. While past research has investigated colloidal accumulation-associated NF/RO rejection of organic micropollutants, this study confirmed that colloidal particles indigenous to a typical surface water matrix negatively impact nanofiltration of PhAC/EDCs.