Hydrodynamic simulation of draw solution flow fields in a submerged Forward Osmosis membrane module

This study aimed to develop an energy-efficient submerged Forward Osmosis (FO) membrane element capable of concentrating wastewater without requiring pretreatment. This objective was achieved by optimizing the Draw Solution flow path using Computational Fluid Dynamics (CFD) techniques. First, the relationship between membrane surface shear strain rate and water flux was clarified through small-cell experiments using commercially available flat-sheet FO membranes. Next, CFD simulations were conducted inside the submerged FO membrane element to obtain the distribution of shear strain rate on the membrane surface. By combining these CFD-derived shear strain rate distributions with the experimentally obtained relationship between shear strain rate and water flux, a new method was developed to calculate the overall water flux of the entire FO element. In a submerged FO membrane pilot unit, the measured overall water flux under varying DS recirculation flow rates agreed well with the corresponding CFD predictions. This integrated approach enables the rational design of submerged FO membrane structures, including baffle arrangements, and provides the basis for Techno-Economic evaluation of optimized flow conditions for large-scale wastewater treatment applications. Based on the Techno-Economic analysis, a draw solution flow rate of 0.2 m 3 m −2 h −1 per membrane surface area was identified as the optimal condition for minimizing the operating cost of the filtration tanks. • Submerged FO membrane performance can be predicted by mathematical models using hydrodynamic attributes at the DS side. • Optimal operation point of submerged FO membrane can be established by combining simulation result and Techno-Economic method. • Baffle is a key factor in increasing the performance of the submerged FO membrane module.