Fig. 2 shows the profiles of the FO

Fig. 2 shows the profiles of the FO permeate flux and the mixed liquor conductivity with the active-layer-facing-the-feed-solution (AL-FS) orientation during a 108-day operation. The conductivity of the mixed liquor increased from 815 to 28,580 mS/cm within the first 50 days. This increase was mainly due to the retention of solutes from the feed by the FO membrane and the reverse diffusion of NaCl from the DS. After 50 days of operation, the conductivity stabilised as a result of the routine daily discharge of 100 ml of mixed liquor and 150 ml of supernatant.