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

Abstract

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.

Cellulose Triacetate (CTA) Hollow-Fiber (HF) Membranes for Sustainable Seawater Desalination: A Review

“…Most recently, CTA-HF membranes have been applied to demonstrate the OARO application because of its high pressure resistance similar to the RO membranes (>70 bar) and the preferable HF configuration which allows two solutions to be introduced at both sides of the membrane [ 34 , 35 ]. Norihiro Togo et al performed OARO concentration tests using a pilot-scale CTA-HF membrane module and a theoretical calculation based on the test results.…”

“…Cellulose triacetate (CTA)-based hollow fiber (HF) membrane is therefore one of the commercially successful semipermeable membranes that has a long historical development due to its reliable excellent performances especially for drinking water production from seawater. In addition, recently, because of the versatile demands in energy consumption and environmental concerns about brine discharge as mentioned above, CTA-based HFs have caught attention for the usage of different methods, such as forward osmosis (FO) [ 23 , 24 , 25 , 26 ], pressure-retarded osmosis (PRO) [ 11 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ] and brine concentration (BC) [ 34 , 35 ] for the emerging technologies. Because their applications require optimum characteristics individually, different strategies for designing the membrane and module are required in spite of using the same CTA material.…”

Ultra-strong polymeric hollow fiber membranes for saline dewatering and desalination

“…Briefly, a saline stream with a lower or equal salinity is employed in the permeate side as a sweep stream of the OARO process to reduce the difference of osmotic pressure across the membrane, thereby the water transport becomes possible even when the osmotic pressure of the feed is larger than the external applied hydraulic pressure 3 , 14 . Therefore, OARO makes a high water recovery of >70% via a membrane-based energy-efficient process possible 3 , 11 , 13 , 14 . Nevertheless, the OARO process is also limited by the burst pressure of the membrane as the water recovery becomes higher 3 , 11 , 13 , 14 .…”

“…Therefore, OARO makes a high water recovery of >70% via a membrane-based energy-efficient process possible 3 , 11 , 13 , 14 . Nevertheless, the OARO process is also limited by the burst pressure of the membrane as the water recovery becomes higher 3 , 11 , 13 , 14 . Thus, the development of strong and efficient membranes is a key in meeting the requirements of the OARO processes.…”

“…Toyobo’s pressure retarded osmosis (PRO) and RO hollow fiber membranes can withstand the maximum pressures of up 29 bar and 69 bar under the out-to-in mode (i.e., from the shell side to the lumen), respectively 21 . However, the pressure drops of its hollow fiber modules are considerably high because its hollow fiber membranes are outer selective (i.e., the selective layer is on the shell side) and small in dimensions (i.e., inner diameter/outer diameter = ~80/180 µm) 13 , 21 – 23 . For example, Togo et al used Toyobo’s PRO hollow fiber membranes for OARO, in which a low pressure of 8–18 bar was applied at the shell side.…”