Bidirectional Permeation of Electrolytes in Osmotically Driven Membrane Processes

Osmotically driven membrane processes (ODMP) are emerging water treatment and energy conversion technologies. In this work, we investigated the simultaneous forward and reverse (i.e., bidirectional) solute fluxes that occur in ODMP. Numerous experiments were conducted using ternary systems (i.e., systems containing three distinct ions) and quaternary systems (i.e., systems containing four distinct ions) in conjunction with a membrane in a forward osmosis orientation. Ten different combinations of strong electrolyte salts constitute the ternary systems; common anion systems studied included KCl-NaCl, KBr-NaBr, KNO3-NaNO3, KCl-CaCl2, and KCl-SrCl2; and common cation systems explored were KCl-KH2PO4, NaCl-NaClO4, NaCl-Na2SO4, NaCl-NaNO3, and CaCl2-Ca(NO3)2. For each combination, two experiments were conducted with each salt being used once in the draw solution and once in the feed solution. Quaternary systems studied were NaCl-KNO3, NaCl-MgSO4, MgSO4-KNO3, and NaCl-K2SO4. Experimental fluxes of the individua...