Integration of nanofiltration and reverse osmosis in desalination of mine water

ABSTRACT The research with natural mine waters coming from Desalination Plant ‘Dębieńsko’ (Southern Poland), taken before reverse osmosis (RO) installation, that is, after standard pretreatment, was carried out. Commercial nanofiltration (NF) membranes produced by the Dow-Filmtec (NF-90) and RO membranes (SW30-2521 of Dow-Filmtec and AD HR-90 by GE) were used in the test. The NF process was carried out at a transmembrane pressure of 1.0 and 1.5 MPa and the RO process at a pressure of 2.5 and 3.0 MPa, depending on the system used. Tests were conducted using the Osmonics Inc. company’s SEPA CF-HP type membrane module, in the high-pressure version in crossflow mode and in some cases in the dead-end mode system. A two-stage treatment system combining NF and RO for the desalination of mine water was used. The desalination efficiency (flux and composition of permeate and concentrate) was determined. The obtained results proved that NF could be an ideal pretreatment step for mine waters during RO desalination process. It enabled to increase the permeate flux of the RO membrane, eliminated the scaling problem and increased the concertation of salt in RO retentate. The use of the NF-90 membrane in the NF + RO desalination system resulted in a lower permeate flux in the NF process, while the flux in the RO process was higher in comparison to the system without NF. Taking into consideration the membrane efficiency results, one can conclude that permeates coming from mine water corresponded to the permissible values for drinking water standard. In addition, water was nontoxic.