Rejection properties of NF membranes for alkylphenols

Alkylphenols (APs), such as nonylphenol, are well-known as endocrine disrupting compounds (EDCs) and have been observed in aquatic environment. In this work, we focused on the rejection properties of NF membranes for APs. The rejection properties for 10 kinds of APs (alkyl group: C2–C9) were examined with four kinds of flatsheet-type NF membranes. The highest desalting membrane (Memb-1) effectively rejected 4-n-octylphenol and 4-n-nonylphenol at the rate of more than 95%, but the APs with lower molecular weight rejected at the lower degree. In the cases of lower desalting membranes, the rejections of the APs increased linearly with the increase of the molecular weight. The adsorption properties of the APs on the membranes were examined by both batch type adsorption experiments and an inverse HPLC technique. In the inverse HPLC experiments, polyamide particulates were used as the stationary phase and CH3OH/H2O (70/30) was used as the mobile phase. The logarithm of capacity ty factor (log k′) of the APs obtained by HPLC method was linearly correlated with the logarithm of the partition coefficient (log K) obtained by the batch type adsorption experiments. Since the log k′ was also correlated linearly with log P, it can be said that the adsorption properties of the APs on the membrane polymer were mainly controlled by the hydrophobic interaction.