A systematic study for predicting the performance of forward osmosis desalination using commercial low-cost superabsorber polymer (SAP) hydrogels as draw agent: water flux enhancement by tailoring process parameters

This study investigates the potential of using low-cost commercial superabsorbent polymers (SAPs) as draw agents in a hydrogel-driven forward osmosis (FO) desalination process. Different types of commercial SAPs were tested, with Evonik weak-crosslinked (EV-WC) hydrogels displaying the highest water flux and swelling ratio. Using EV-WC as the draw agent, the initial water flux was approximately 0.96 LMH with 200-300 µm size hydrogels for a 2000 ppm NaCl solution. Water flux improved with smaller hydrogel particles, achieving 1.02 LMH with 100-200 µm particles, while larger particles (> 600 µm) yielded 0.75 LMH. Increasing the mass of hydrogels on the membrane surface also enhanced water flux; doubling the hydrogel mass from 0.1 to 0.2 g increased initial water flux from 0.8 to 1.03 LMH, and doubling it again from 0.2 to 0.4 g raised the flux to 1.51 LMH. Adding a slight weight above the hydrogels to ensure better contact with the membrane surface further improved water flux. This study demonstrates the effectiveness of EV-WC hydrogels as draw agents and provides insights into optimizing conditions for improved FO desalination performance. Increasing the hydraulic pressure from 40 to 50 cm resulted in a 37% increase in initial water flux while its increasing from 50 to 57 cm yielded a 7% augmentation in initial water flux. Water recovery from swollen hydrogels has been studied using our own developed specialized press by the application of external pressure to extract water from swollen hydrogels. The results indicate that when the pressure is increased from 1 bar to 75 bar at a rate of 60 bar/hr, approximately 250 J of energy is required to recover 300 mL of water.