Progress in Forward Osmosis Membrane Separation Process

Abstract

Forward osmosis (FO) has been extensively investigated and demonstrated its advantages in a range of FO applications over the past decade. However, challenges still remain in terms of the lack of both efficient FO membranes and appropriate draw solutes for practical FO applications. To promote the advancement of FO technology, considerable efforts have been made in exploring novel FO membranes and draw solutes in recent years. This paper will provide a short review on the progress of both FO membranes and draw solutes. First of all, a brief overview on FO principle is given. Then the progress in FO technology related to FO membrane and draw solute is presented with specific examples. Finally, challenges and future directions of FO technology in exploring efficient FO membranes and promising draw solutes are also highlighted. This article may provide new insights into the future development of FO technology and promote practical FO applications.Keywords forward osmosis, draw solution, forward osmosis membrane, forward osmosis application IntroductionFreshwater shortage has been becoming a more and more severe problem globally. [1][2][3][4] To mitigate this problem, various technologies for clean water production have been explored worldwide recently. [5][6][7][8][9] Membrane technology has shown a great potential in water treatment in view of the advantages of no phase change, strong adaptability, relatively simple operation and low cost. [5,[10][11][12] A range of pressure-driven membrane processes, such as microfiltration (MF), [13][14][15][16] ultrafiltration (UF), [13,17,18] nanofiltration (NF), [19][20][21] and reverse osmosis (RO) [22][23][24][25][26] have been extensively used for clean water production through either wastewater reuse or brackish water/ seawater desalination. However, some issues, such as severe membrane fouling, low water recovery rate, intensive-energy consumption and relatively low quality of product water, occur frequently during these processes. [10,13,17,23,27] FO has been recognized as a promising membrane process because of the following characteristics: (1) no requirement of hydraulic pressure; (2) a relatively high water recovery rate; (3) low membrane fouling propensity due to the absence of hydraulic pressure; (4) environmental friendliness. Given these merits, FO technology has been applied to a wide range of fields, such as seawater/brackish water desalination, [4,24,28] wastewater treatment, [8,[29][30][31] and many other areas. [32][33][34][35][36] Although FO exhibits a great potential in alleviating the issues caused by freshwater shortage, challenges, such as relatively low water permeability, high reverse solute diffusion, severe concentration polarization (CP), and membrane fouling, are still present in FO applications. [37][38][39] To eliminate these problems, exploration of appropriate semi-permeable FO membrane and draw solute is urgently needed. Great efforts have been made in the development of FO technology in recent years, and a wide range of powerful FO membra...