Unraveling relative roles of bulk precipitation and surface growth in developing a scaling layer in membrane distillation
Scaling of sparingly soluble salts is a challenge standing in the way of enhancing water recovery of desalination via an approach based on membrane distillation (MD). Improvement of anti-scaling strategies is dependent on understanding various mechanisms accounting for evolution of the scaling layer. This study made efforts to address a fundamental concern as to how bulk precipitation is competing with surface growth to form a layer of crystalline particles in the process of MD. When concentrating a feed containing calcium sulfate , scaling was induced in a series of MD processes with a varied transmembrane temperature difference. In addition to the measurements of flux decline and electrical conductivity , optical coherence tomography (OCT) was explored to simultaneously monitor the formation of crystals in the feed bulk and resolve the scaling layer evolving on the membrane surface . Comparison of these characterization results revealed the key role of surface growth in initiating the scaling, while suggesting that the cake development could be gradually dominated by the deposition of crystals formed in the feed bulk. A further analysis of the local growth rates provided deeper insights into the mechanistic transition; effects of varying the degree of supersaturation were also discussed in the context of redistributing the size of deposits and inducing the crystal-membrane interactions. This study refines the picture of developing a scaling layer in MD, which would be of great value in advancing applications of MD-based desalination.
危险品化学品经营许可证（带存储）