Dynamic Relationship Between Reverse Solute Flux and Membrane Fouling in Forward Osmosis
Membrane fouling poses a limitation to the application of forward osmosis(FO),and reverse solute flux(RSF)from the draw solutes further reduces the permeability of the membrane.Therefore,this study investigated the dynamic relationship between reverse solute flux and organic membrane fouling using typical inorganic draw solutions(DSs)(NaCl,NaHCO3,NaH2PO4,NH4Cl,CaCl2).On one hand,the reverse solute flux directly interacted with the membrane fouling layer,affecting its configuration.For example,the reverse flux of Ca2+from CaCl2 draw solute readily crosslinked with sodium alginate(SA),forming a three-dimensional network structure that exacerbated membrane fouling.On the other hand,the formation of membrane fouling reduced the reverse flux of Ca2+from CaCl2 draw solute(5.8±1.6 mmol·m-2·h-1)while increasing the reverse diffusion of NH4 from NH4Cl draw solution(129.2±12.8 mmol·m-2·h-1).Consequently,the water recovery using NH4Cl as the draw solute(151.4±10.6 g)was lower than that using CaCl2(246.4±124.7 g).Furthermore,reverse solute flux altered the properties of the feed solute,leading to the dominance of different filtration mechanisms in the formation of membrane fouling,which subsequently impacts the degree of fouling.
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