Assessment of ultrasound-assisted forward osmosis process performance for seawater desalination using experimental factorial design

The effect of ultrasound on water flux through forward osmosis membrane for seawater desalination was investigated using the factorial design approach. Sodium chloride (NaCl) was used to simulate the dissolved solids content. In every test, the initial draw solution (DS) concentration was fixed at 4.5 M for NaCl and 2 M for MgCl2. Parameters considered in the investigation included membrane crossflow velocity (0.25 and 1.0 cm/s), flow configuration (co-current versus counter-current), direction of ultrasound waves relative to the membrane side (active layer versus support layer), and type of draw solution (NaCl versus MgCl2). A two-level factorial design was considered in the analysis of the results obtained from the experimental work. Based on the factorial design analysis, crossflow velocity and use of ultrasound have a positive effect on water flux enhancement for both draw solutions. However, the velocity effect on water flux enhancement was more pronounced than that of the use of ultrasound. The effect of flow configuration was statistically insignificant for both draw solutions. The interaction effect between crossflow velocity and ultrasound was statistically significant for both draw solutions. However, the interaction between crossflow velocity and flow configuration was only significant for the case of MgCl2. The three-way interaction was insignificant for both draw solutions. The developed factorial model equations were used to predict other flux data in ultrasound-assisted FO systems and showed adequate representation of these data at relatively similar conditions after adjustment of the model for the baseline conditions of the evaluated cases.