on polysulfone thin film composite (e.g. TFC–S,
TFC–ULP) membranes were found desirable for
the removal of estrogens (estrone) since adsorption
was the dominant removal mechanism [66].
The retention was initially good and once the
membrane became saturated, the permeate concentration
remained lower than the feed, indicating
sieving occurred. No decline in estrone
retention occurred after adsorption had stopped
when using polyamide on urea TFC. This is
because the X-20 RO membrane has a smaller
pore size than TFCs. There is no breakthrough
curve for the tighter membrane since diffusion is
the dominant mechanism and separation is
accomplished via sieving [66,69].