Xiao Ping, Liu Liang
Green Intelligence Environmental School, Yangtze Normal University, No. 16 Juxian Road, Fuling District, Chongqing 408100, China.
Membranes (Basel). 2025 Jul 25;15(8):223. doi: 10.3390/membranes15080223.
Concentration polarization (CP) is one of the inherent problems that lowers the operating performance of forward osmosis (FO) membranes. Therefore, a quantitative evaluation of CP is vital to understand its impact on the FO process. This study systematically investigated the influences of different CPs on the osmotic pressure drop across the membrane under different conditions by using the water transmission coefficient, η, defined as the ratio of the measured water flux to the theoretical water flux. The results showed that η decreased with an increase in the concentration gradient between the draw solution (DS) and the feed solution (FS) under different conditions. The proportions of osmotic pressure drop caused by dilutive internal concentration polarization (ICP) increased, while those caused by concentrative external concentration polarization (ECP) decreased, in different types of DSs in FO mode. Both ECP and ICP were found to be capable of reducing osmotic pressure. However, the internal CP had the dominant influence. To better understand the adverse effects of CP, using an organic FS provided greater insight than using deionized (DI) water as the FS. As the FS concentration increased, the water flux reduced, and the adverse effects of CP worsened. CaCl led to a greater reduction in water transfer efficiency than NaCl when used as the DS. In comparison to FO mode, pressure-retarded osmosis (PRO) mode led to greater pure water flux and flux decline. In FO mode, both the proportion of dilutive ICP and the η decreased, while the proportion of concentrative ECP increased over time. However, in PRO mode, the proportions of dilutive ECP and concentrative ICP increased, and η gradually decreased. Dilutive ICP had a significant negative effect on osmotic pressure in the former, while dilutive ECP was dominant in the latter.
浓差极化（CP）是降低正向渗透（FO）膜运行性能的固有问题之一。因此，对浓差极化进行定量评估对于了解其对正向渗透过程的影响至关重要。本研究通过使用水传输系数η系统地研究了不同浓差极化在不同条件下对跨膜渗透压降的影响，η定义为测量的水通量与理论水通量之比。结果表明，在不同条件下，η随汲取液（DS）和进料液（FS）之间浓度梯度的增加而降低。在FO模式下，不同类型的汲取液中，由稀释性内浓差极化（ICP）引起的渗透压降比例增加，而由浓缩性外浓差极化（ECP）引起的渗透压降比例降低。发现ECP和ICP均能够降低渗透压。然而，内浓差极化具有主导影响。为了更好地理解浓差极化的不利影响，使用有机进料液比使用去离子（DI）水作为进料液能提供更多的见解。随着进料液浓度的增加，水通量降低，浓差极化的不利影响加剧。当用作汲取液时，CaCl2导致的水传输效率降低比NaCl更大。与FO模式相比，压力延迟渗透（PRO）模式导致更高的纯水通量和通量下降。在FO模式下，稀释性ICP的比例和η均降低，而浓缩性ECP的比例随时间增加。然而在PRO模式下，稀释性ECP和浓缩性ICP的比例增加，且η逐渐降低。在前者中，稀释性ICP对渗透压有显著负面影响，而在后者中，稀释性ECP占主导。
