The adsorption mechanism has been correlated
with solute–membrane hydrophobic interactions
[63,66,69]. Hydrophobic interaction between
membrane and solutes is one of nanofiltration’s
important rejection mechanisms. Hydrophobicity
of membranes is usually characterized by their
contact angle whereas hydrophobicity of solutes
can be correlated and quantified with logarithm of
octanol-water partition (log Kow). Molecules with
log Kow>2 are usually referred to hydrophobic
ones [48,70]. Octanol/water partition coefficient
values are determined as log [ratio of the concentration
in the octanol phase to the concentration in
the aqueous phase at adjusted pH] in such that the
predominant form of the compound is un-ionized.
According to the work by Yoon et al. [63],
hydrophobic adsorption (to hydrophobic NF) that
takes place during the initial operational period
depends on hydrophobicity of compounds to be
separated. Hydrophobic properties have an influence
on the sorption mechanism where strong
hydrophobic compounds as aromatic pesticides,
non-phenylic pesticides and alkyl phthalates were
highly rejected even by the lowest desalting
membrane [71]. However, the retention decreases
as sorption reduces after the saturation of the
membrane. This shows that the initial adsorption
of hydrophobic molecules on NF membranes will
be high, which causes a high initial rejection