Quantifying the influence of divalent cations mass transport on critical flux and organic fouling mechanism of forward osmosis membrane

Abstract Understanding the insightful impact of divalent cations mass transport on the complex organic fouling of forward osmosis (FO) membrane is vital when seawater/brine is utilized in a FO hybrid process. Our works deeply focused on quantifying the influence of divalent cations on not only critical flux but also the organic fouling mechanism. The presence of divalent cations in aqueous solutions caused a decrease in critical flux values. The fouling mechanism is mainly governed by intermolecular and ion-mediated interactions. The findings suggested the interaction of divalent cations with organic matters close to the membrane surface is more noticeable than that in the feed solution. These interactions combined with an operation at the flux ≥30 LMH led to the formation of a compact and cohesive cake layer (4.8–9.1 μm) where the great divalent cations were deposited on membrane surface after 30 h operation (Ca2+: 162.13–256.72 g/m2, Mg2+: 182.60–374.38 g/m2). In contrast, 21 LMH below critical value exhibited minor fouling with a very thin cake layer (0.5 μm) and minimized deposited divalent cations (Ca2+: 79.47 g/m2, Mg2+: 46.65 g/m2). Overall, the extended operation of 30 h suggested 16–21 LMH were threshold values for FO fouling control.