Multistage osmotically assisted reverse osmosis process for concentrating solutions using hollow fiber membrane modules

• Published in: Chemical engineering research & design 2020-10, Vol.162, p.117-124
• Main Authors: Nakagawa, Keizo, Togo, Norihiro, Takagi, Ryosuke, Shintani, Takuji, Yoshioka, Tomohisa, Kamio, Eiji, Matsuyama, Hideto
• Format: Article
• Language: English
• Subjects: Cellulose; Cellulose fibers; Cellulose triacetate; Cellulose triacetate membrane; Concentration polarization; Hollow fiber membrane module; Hollow fiber membranes; Membranes; Modules; Multistage concentration process; Osmosis; Osmotically assisted reverse osmosis; Pressure; Reverse osmosis; Water purification
• ISSN: 0263-8762; 1744-3563
• DOI: 10.1016/j.cherd.2020.07.029

[Display omitted] •Solution concentration using multistage osmotically assisted reverse osmosis (OARO) system was performed.•Two types of hollow fiber (HF) membrane modules with different numbers of HFs were used.•Feed solution was concentrated by the OARO process even using highly concentrated NaCl solutions and low applied pressures.•A multistage system produced a higher degree of concentration as compared with a single stage system.•Water flux and concentration ratio were influenced by the internal concentration polarization in the modules. Reverse osmosis (RO) is commonly used to concentrate solutions in food preparation and environmental applications among others. Limitations on the applied pressure, which must be higher than the osmotic pressure of the feed solution, determine the concentration that can be achieved by RO. Recently, an osmotically assisted reverse osmosis (OARO) system that can be operated even with low applied pressure has been suggested as a new concentration process. In this study, we performed concentration tests on a multistage OARO system that used two types of hollow fiber (HF) membrane modules made from cellulose triacetate with different numbers of HFs. Water permeated through the membrane and the concentration increased as it progressed through the modules, even when using concentrated NaCl solutions (1.0 and 2.0 M) with low applied pressures (10 and 15 bar). The concentration increased in each of ten stages in a multistage concentration test. Water flux and concentration ratio were strongly influenced by the internal concentration polarization in the modules.