Nanofiltration of trace organic chemicals: A comparison between ceramic and polymeric membranes

• TrOC rejection by ceramic and polymeric NF membranes was governed by size exclusion.
• There were differences in rejection behaviours of ceramic and polymeric membranes.
• Hydrophobic interaction was less significant in TrOC separation by ceramic membrane.
• Electrostatic interaction also affected charged TrOC rejection by ceramic membrane.
• Negative TrOCs were better rejected by ceramic membrane than positive ones.

The rejection of 41 trace organic chemicals (TrOCs) by a ceramic nanofiltration (NF) membrane was examined and compared with that by two polyamide-based NF membranes – namely NF90 and NF270. Rejection behaviours of TrOCs by the ceramic and polymeric NF membranes were mostly similar but there were several notable differences. The rejection of neutral TrOCs by the ceramic and polymeric NF membranes increased in the order of increasing molecular size (e.g. minimum projection area), indicating that size exclusion is the dominant mechanism governing rejection. However, in contrast to the polymeric NF membranes, where hydrophobic interaction between membrane and TrOCs influenced the rejection of neutral molecules, the impact of hydrophobic interaction was not significant for the ceramic NF membrane. The rejection of low molecular weight TrOCs increased in the order of NF270, NF90 and ceramic NF membranes, while molecular weight cut-off increased in the order of ceramic NF, NF270 and NF90 membranes. A notable difference of about 20% in rejection between positively and negatively charged TrOCs of similar molecular size was observed for the ceramic NF membrane but not the two polymeric ones. The results indicate that electrostatic repulsion and attraction of charged TrOCs with the ceramic membrane differ from those with polymeric membrane materials.