(1) a constant-recovery experiment where both concentrate and permeate streams were circulated back to the feed tank, maintaining a constant feed composition; and (2) an increasing-recovery experiment where only the feed stream was recirculated to the feed tank and the permeate was collected in a different tank, thus concentrating the feed. In both cases, the initial feed solution simulated a concentrate stream obtained by applying RO to the ED diluate with an ~88% recovery ratio (with concentration factors of initally ~8.3 and up to ~12.5 in the increased-recovery mode). To avoid gypsum supersaturation due to concentration polarization or fluctuations in solution composition and temperature, the maximal experimental recovery ratio was set to 92%, which is lower than the 95.5% threshold reached in the PHRREQC geochemical simulation. The feed solution was adjusted to pH > 2, the limit for polyamide membrane operation . Scaling risk was assessed by running the experiments at constant pressure for several days while monitoring their performance and analyzing the membrane surface after filtration.