Study of Reverse Solute Flux in Apple Juice Concentration by Forward Osmosis

Reverse solute flux(RSF) is a big challenge of forward osmosis(FO) technology. This experiment was based on the study of the performance of apple juice concentration by FO technology and the solute diffusion law of functional draw solution(sodium acetate, sodium bicarbonate and sodiumcitrate). Firstly, the basic properties of FO system were studied, including water flux, RSF and rejection rate, by varying the concentration of NaCl draw solution, influent flow rate and membrane operation mode. The concentration ability of deionized water and apple juice and solute diffusion law were analyzed. To achieve the purpose of converting the RSF into advantages, the effect of different functional draw solutions on apple juice concentration and RSF were compared. The results showed that the concentration efficiency and RSF were affected by the concentration of draw solution and membrane operation mode. The membrane mode of pressure retarded osmosis(PRO) led to the higher RSF and the concentration degree of apple juice than the FO mode. In the PRO mode, the RSF reach to 87.34±6.32 g·m⁻²·h⁻¹ with the NaCl draw solution concentration of 5 mol·L⁻¹. The ability of concentrating apple juice by different concentration of functional draw solution was various. The order of water extraction capacity from high to low was sodium bicarbonate, sodium chloride, sodium acetate, sodium citrate and the order of RSF from high to low was sodium citrate, sodium bicarbonate, sodium chloride, sodium citrate. The RSF was 29.61±2.19 g·m⁻²·h⁻¹ with 2 mol·L⁻¹ NaCl draw solution, which was only half of the same concentration of NaCl draw solution. Compared with traditional NaCl draw solution, sodium citrate draw solution could effectively control RSF.