Elucidating the Rejection Mechanisms of PPCPs by Nanofiltration and Reverse Osmosis Membranes

Abstract

In this study, the rejection mechanisms of six commonly detected pharmaceutical and personal care products (PPCPs) were systematically studied with three commercial thin film composite polyamide reverse osmosis (RO, XLE) and nanofiltration (NF, NF90, and NF270) membranes at pH 3–10. The amount of PPCP adsorption on membrane surfaces was also extracted and calculated so as to determine the contribution of adsorption mechanism on PPCP rejection using adsorption kinetics and adsorption isotherms. At low pHs, PPCP rejection was the highest for XLE followed by NF90 and NF270. As pH increased to 10, PPCP rejection increased significantly for NF90 and NF270, attributed to the enhanced electrostatic repulsion between the negatively charged membrane surface and ionized PPCPs, while being slightly increased for XLE due to the dominant mechanism of steric hindrance. The simplified charge concentration polarization model predicted well for most cases, which demonstrated the contribution of steric hindrance and electr...