The critical failure mode for membrane distillation (MD) desalination is wetting through the pores of the hydrophobic membrane, which allows the saline solution to leak through and contaminate the permeate. The standard practice for reversing membrane wetting is to dry out the membrane for several hours before resuming the desalination process. An alternative method for mitigating MD membrane wetting is examined in this study, wherein pressurized air is pushed through the membrane from the permeate side for several seconds, forcing trapped water out before it can evaporate. To compare the wetting reversal methods, the liquid entry pressure (LEP) was surpassed with saline water at varied salinity. Then, either a 24+ hour dryout, a 10 second pressurized air treatment, or both were applied, followed by remeasuring the LEP. Pressurized air backwashing restored the LEP to 75% of the original value for lower salinity feeds. The backwashing method is hypothesized to achieve this superior result because it removes saline solution from the membrane without separating water and salts by vaporization, whereas the dryout method causes seawater within the membrane to evaporate, leaving crystalline solutes trapped within the membrane. Such trapped particles may act as a path for rewetting, and also impair permeate flux and system energy efficiency. For all three methods, membranes tested with higher salinity water had lower LEP restoration irrespective of the restoration technique used. A method for testing LEP with more accuracy was also developed, using stepwise pressure increases. SEM images showed that the restoration methods did not alter the membranes themselves, although there remains a possibility that the air backwashing can cause superficial tears.

中文翻译：

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逆向膜蒸馏中的膜润湿：将干燥与加压空气的反冲洗进行比较

膜蒸馏（MD）脱盐的关键失效模式是通过疏水膜的孔润湿，这会使盐溶液泄漏并污染渗透液。扭转膜润湿的标准做法是在恢复脱盐过程之前将膜干燥数小时。在这项研究中，研究了另一种减轻MD膜湿润的方法，其中加压空气从渗透物侧被推动穿过膜达数秒钟，迫使被困的水在蒸发之前被排出。为了比较润湿逆转方法，在不同盐度下，盐水都超过了液体入口压力（LEP）。然后，要么进行24小时以上的干透，要么进行10秒钟的加压空气处理，或者同时进行这两种处理，然后对LEP进行重新测量。加压空气反冲洗可将LEP恢复至原始盐度值的75％（盐度较低的饲料）。假设使用反洗方法可达到这一优异效果，因为它可以从膜中除去盐溶液，而不会通过汽化分离出水和盐，而干燥方法会使膜内的海水蒸发，从而将结晶溶质截留在膜内。此类捕获的颗粒可能充当重新润湿的路径，并且还会削弱渗透通量和系统能效。对于这三种方法，无论采用何种修复技术，用高盐度水测试的膜的LEP修复率均较低。还开发了一种使用逐步增加压力的方法来测试LEP的准确性更高。扫描电镜图像表明，修复方法并没有改变膜本身，