Osmotically Assisted Reverse Osmosis Utilizing Hollow Fiber Membrane Module for Concentration Process

Solution concentration processes such as evaporation, freeze concentration, and reverse osmosis are commonly used in food processing and environmental applications. However, these processes are frequently examined to lower energy costs and improve concentration ratios. This study performed concentration tests and theoretical calculations for osmotically assisted reverse osmosis (OARO) using a pilot-scale hollow-fiber membrane module. In the concentration test using NaCl solution, water flux and concentration ratio were measured with changing flow rate, concentration, and applied pressure. Water permeation and solution concentration were achieved, even using concentrated salt solutions (0.5 and 1.0 M), with applied pressure of 8–12 bar, which was lower than the osmotic pressure (25 bar for 0.5 M NaCl; 50 bar for 1.0 M NaCl). The calculation results were in good agreement with the experimental results, and the validity of the calculation model was confirmed. Analysis revealed that the concentration gradient and concentration polarization in the module changed with operating conditions, and these factors affected the water flux and the concentration ratio.