Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Environ Sci Technol. 2021 Apr 20;55(8):5442-5452. doi: 10.1021/acs.est.1c00435. Epub 2021 Mar 12.
Cake layer formation is the dominant ultrafiltration membrane fouling mechanism after long-term operation. However, precisely analyzing the cake-layer structure still remains a challenge due to its thinness (micro/nano scale). Herein, based on the excellent depth-resolution and foulant-discrimination of time-of-flight secondary ion mass spectrometry, a three-dimensional analysis of the cake-layer structure caused by natural organic matter was achieved at lower nanoscale for the first time. When humic substances or polysaccharides coexisted with proteins separately, a homogeneous cake layer was formed due to their interactions. Consequently, membrane fouling resistances induced by proteins were reduced by humic substances or polysaccharides, leading to a high flux. However, when humic substances and polysaccharides coexisted, a sandwich-like cake layer was formed owing to the asynchronous deposition based on molecular dynamics simulations. As a result, membrane fouling resistances were superimposed, and the flux was low. Furthermore, it is interesting that cake-layer structures were relatively stable under common UF operating conditions (i.e., concentration and stirring). These findings better elucidate membrane fouling mechanisms of different natural-organic-matter mixtures. Moreover, it is demonstrated that membrane fouling seems lower with a more homogeneous cake layer, and humic substances or polysaccharides play a critical role. Therefore, regulating the cake-layer structure by feed pretreatment scientifically based on proven mechanisms should be an efficient membrane-fouling-control strategy.
蛋糕层形成是长期运行后超滤膜污染的主要超滤膜污染机制。然而，由于其厚度很薄（微/纳米级），精确分析蛋糕层结构仍然是一个挑战。在此，基于飞行时间二次离子质谱的出色深度分辨率和对污垢的识别能力，首次在较低的纳米尺度上对天然有机物引起的蛋糕层结构进行了三维分析。当腐殖质或多糖分别与蛋白质共存时，由于它们的相互作用，形成了均匀的蛋糕层。因此，腐殖质或多糖减少了蛋白质引起的膜污染阻力，从而导致通量增加。然而，当腐殖质和多糖共存时，由于基于分子动力学模拟的异步沉积，形成了三明治状的蛋糕层。结果，膜污染阻力叠加，通量较低。此外，有趣的是，在常见的 UF 操作条件（即浓度和搅拌）下，蛋糕层结构相对稳定。这些发现更好地阐明了不同天然有机物混合物的膜污染机制。此外，研究表明，具有更均匀的蛋糕层时，膜污染似乎较低，腐殖质或多糖起着关键作用。因此，根据已证明的机制，通过进料预处理科学地调节蛋糕层结构应该是一种有效的膜污染控制策略。
