Evaluation of sodium acetate and glucose as minor additives with calcium chloride as optimum mixed draw solutes for fruit juice concentration via forward osmosis

The selection of an appropriate draw solution is decisive to augment the performance of the forward osmosis (FO) process with maximal permeate flux and minimal reverse solute flux. Inorganic salts provide higher permeate flux in FO, but high reverse salt flux (RSF) associated with greater diffusivity limits their potential application. Herein, the incorporation of organic compounds including sodium acetate (NaAce) and glucose in CaCl₂ provides draw solutions with constant osmotic pressure for boosting FO performance. The PRO mode (active layer facing draw solution) is examined with 0.18m/s of cross-flow velocity using a polyamide membrane associated with a polyethyleneimine (PEI) interlayer on a NaOH treated polyacrylonitrile substrate. The 5% NaAce with CaCl₂ as a draw solution (DS) delivers better performance against deionized water compared to glucose, resulting in lower RSF (6.64 g/m² h) and higher water flux (23.9 L/m² h). The NaAce with CaCl₂ suppresses RSF up to 41% without a significant reduction in permeate flux compared to single salt DS. The optimized draw solution concentrates the orange juice, resulting in 2.13 L/m² h of average water flux and 3.6 g/m² h of RSF for 72 h, thus concentrating the orange juice from the initial concentration of 13 °Brix to 24 °Brix.