CFD analysis of PBI and PSF membranes with MWCNT for water recovery from brackish water RO reject by FO and validation with experimental results

As global water scarcity intensifies, sustainable alternatives to reverse osmosis (RO), which is an energy-intensive process, are essential, especially given the environmental risks posed by wastewater and brackish water discharge. This study explores forward osmosis (FO) as a viable alternative, using 2M MgCl 2 as the draw solution (DS) and brackish water RO reject as the feed solution (FS). In the present work, a computational fluid dynamics (CFD) study is performed to model water transport through FO membranes using two thin-film flat sheet membranes—polysulfone (PSF) and polybenzimidazole (PBI)—enhanced with MWCNT additives, aiming to recover water from brackish water RO reject. This type of CFD evaluation of MWCNT-modified FO membranes is a unique aspect of the present work. A non-Darcy porous medium model was applied in CFD to simulate flow through the FS, DS, and the membrane, with pressure drop correlated to the osmotic pressure gradient. The PBI/MWCNT 2 wt% membrane achieved the best overall performance with a CFD-predicted WF of 31.5 L/m 2 .hr or LMH, closely aligning with the experimental value of 31.2 ± 0.4 LMH. The CFD results for all the membranes are also in close agreement with the experimental data, confirming the accuracy of the model. The WF in the PBI and PBI/MWCNT membranes has a greater effect than the PSF and PSF/MWCNT membranes due to its affinity for water, the π–π bonds between PBI and MWCNT, and the interaction of nitrogen atoms on its imidazole ring with water, forming hydrogen bonds.