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

Membrane filtration is a promising technology to remove hazardous organic m icro-pollutants, such as pesticides, dyes, and many other synthesized produ cts. In our previous work we demonstrated that nanofiltration (NF) membrane s can reject effectively non-phenylic pesticides and alkyl phthalates and t hat 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 t ricyclazole. Although the other membranes showed lower rejections, some pes ticides, such as isoxathion, chloroneb, and esprocarb, were rejected at ver y high rates (> 95%) by all membranes. All the pesticides are adsorbed on t he membranes and the experiment indicates that adsorption properties were c ontrolled by both hydrophobicity (n-octanol/water partition coefficient: lo g P) and molecular shape of the solute. The solute permeability of a pesticide for each membrane can be expressed a s 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 c ase of hydrophobic pesticides. (C) 2001 Elsevier Science B.V. All rights re served.