Effects of hydrophobicity and molecular size on rejection of aromatic pesticides with nanofiltration membranes

Membrane filtration is a promising technology to remove hazardous organic micro-pollutants, such as pesticides, dyes, and many other synthesized products. In our previous work we demonstrated that nanofiltration (NF) membranes can reject effectively non-phenylic pesticides and alkyl phthalates and that hydrophobilicty of these compounds is an important factor for membrane separation. In this work, we examine and report on the rejection properties of 11 kinds of aromatic pesticides by NF membranes (nominal NaCl rejection is 92, 60, 51 and 15%). The highest desalting membrane rejected all pesticides at >92.4%, except tricyclazole. Although the other membranes showed lower rejections, some pesticides, such as isoxathion, chloroneb, and esprocarb, were rejected at very high rates (>95%) by all membranes. All the pesticides are adsorbed on the membranes and the experiment indicates that adsorption properties were controlled by both hydrophobicity (n-octanol/water partition coefficient: log P) and molecular shape of the solute. The solute permeability of a pesticide for each membrane can be expressed as a linear combination of the following two factors: adsorption property on the membranes, and molecular width (MWd) of the solutes. We conclude that steric hindrance is an important factor for solute permeation even in the case of hydrophobic pesticides.