REMOVAL OF XENOESTROGENS FROM WATER DURING REVERSE OSMOSIS AND NANOFILTRATION - EFFECT OF SELECTED PHENOMENA ON SEPARATION OF ORGANIC MICROPOLLUTANTS

Reverse osmosis and nanofiltration are membrane separation processes used to remove low - molecular weight organic micropollutants from water. Investigations in this field focus on the effect of unfavourable phenomena concomitant with membrane filtration, such as adsorption, fouling and concentration polarization on membrane separation of removed organic micropollutants. This study investigated the effect of adsorption and concentration polarization on the removal of four xenoestrogenic compounds i.e. 4 - tert - octylphenol, 4 - nonylphenol, bisphenol A and bisphenol F. Furthermore, a reservoir of micropollutants adsorbed on the membrane surface was desorbed. Reverse osmosis yielded much better results in xenoestrogens removal compared to nanofiltration carried out for comparative reasons. However, the osmotic membrane showed high sorptive properties towards the xenoestrogens. The fundamental feature of adsorption is the formation of hydrogen bridges between membrane polymer and a compound being removed, and the process itself is reversible. The desorption of adsorbed micropollutants involved filtration of an electrolyte solution of pH > pK(a) of the compound. It has been found that concentration polarization brings about a decrease in xenoestrogens retention during reverse osmosis. For nanofiltration at similar filtration conditions, retention of micropollutants increased probably due to the mixed separation mechanism in the process i.e. sieve mechanism with accompanying concentration polarization and fouling.