Effect of membrane properties and pretreatment on flux and NOM rejection in surface water nanofiltration

Nanofiltration (NF) is a compact process that has potential for removing organic and inorganic pollutants for drinking water. In this study, various NF membranes for surface water treatment were compared using a batch-stirred cell and crossflow equipment in terms of solute rejection and membrane flux. The rejection of natural organic matter (NOM) was closely related to ion rejection and membrane flux. To better control NOM, NF membranes having an effective MWCO of less than 200 Da were required due to the bimodal distribution of NOM in surface water. The flux of NF membranes was related to their hydrophobicity and charges. Fouling by NOM adsorption was an important factor in hydrophobic and positively charged membranes, whereas, it was negligible for hydrophilic and negatively charged membranes. Ozone pretreatment was ineffective for controlling NF fouling, whereas, pretreatment by means of PAC or UF showed a remarkable improvement in flux, indicating that the removal of colloids is crucial for preventing NF fouling.