The nanofiltration process was performed using a tangential
filtration system on a pilot scale (Fig. 1) equipped with a spiral
membrane module (Osmonics membranes, HL2521TF, Minnetonka,
USA), with an approximate molecular weight cut-off
of 150–300 Da, 0.9 m2 of filtration area and 98% rejection of
MgSO4 as specified by the manufacturers with a spiral module
at 25 ◦C and 690 kPa.