Fig. 2. Impacts of using KOH as a draw solution of FO processes to extract clean water from wastewater effluent.

a Water flux (J_w) and reverse salt flux (RSF) of the FO process with simulated wastewater effluent containing sodium acetate, NH₃/NH₄⁺, and chloride as feed solution and 1 M KOH as draw solution for five cycles. The dashed lines represent five cycles of 5 h each. (Conditions: [NaAc] = 7.5 mM, [NH₃/NH₄⁺] = 2.2 mM as N, [Cl^–] = 4.2 mM, and flow rate = 70 ml min^–1); b comparison in water flux (J_w) and RSF between the pristine membrane and the 5-cycle used membrane using deionised water as feed solution and 1 M NaCl as draw solution. The inset figure shows the reverse salt flux from the two membranes (error bars represent standard deviation from two independent replicates); c SEM images showing the surface morphology of the selective layer on the pristine membranes; d SEM images showing the surface morphology of the selective layer on the 5-cycle used membrane; e the rejection of sodium acetate, ammonia, and chloride by the FO membrane using 1 M KOH as draw solution (conditions: [Sodium acetate] = 7.5 mM, [Ammonia] = 2.2 mM as N, [Chloride] = 4.2 mM, and flow rate = 70 ml min^–1); f J–V curves for 1 M KOH and 1 M KOH mixed with different impurities including sodium acetate, ammonia, and chloride (error bars represent standard deviation from three independent replicates). Source data are provided as a Source Data file.