Novel insights into the morphological effects of trace organic contaminants on water/PhAC selectivity in nanofiltration of sewage.

Rare understanding is available on the interactions between trace organic contaminants and other components in raw micro-polluted waters, let alone the influence of relevant morphological effects on the membrane-based selective removal performance. To this end, this paper focused on exploring the morphological characteristics of trace pharmaceutically active compounds (PhACs) in sewage, and their impacts on water/PhAC selectivity of a home-made nanofiltration (NF) membrane. The experimental results demonstrated that strong solute-solute affinity interactions between trace PhACs and the coexisting components, including residual particulate matter (<0.45 μm), soluble internal/exogenous organics and hardness ions did present in treated sewage. In specific, the speciation of all selected small-sized PhACs with diverse attributes in an ideal solution surprisingly changed to hydrophobic DOM/colloidal particle-associated state (88.4 %-98.2 %) with molecular weight greater than 3.0 kDa (59.1 %-91.5 %). Consequently, the water/PhAC selectivity of an as-fabricated NF membrane improved by more than an order of magnitude in actual municipal sewage. The nominal molecular weights of DOM-associated state PhACs were positively correlated with the hydrophobicity (Log Kow) of target contaminants. In short, this study provides new insights into the high membrane performance in rejection of PhACs in municipal sewage from the perspective of occurring speciation.