Towards the design of sustainable antifouling system for the filtration of produced wastewater using membrane technology

由于污染导致的膜性能下降每年要花费数百万美元用于过程清洗和修复。一旦被污染的膜变得过时，处理它们可能会导致关闭流程或旁路到新的生产线。不幸的是，由于污染导致的渗透通量下降发生在相对较短的时间内，这使得经常更换污染的机组变得困难。因此，一个可持续的系统需要更长的膜操作时间，以便于对污染的膜进行操作。因此，发明消除和减少污染问题的技术有利于膜工业、过滤技术，最终有利于环境。已经使用了不同的方法来清洁污染的膜，通常可以分为基于化学和物理的技术。化学方法使用各种化学物质来溶解积聚的物质或改变膜表面的亲和力。然而，这些化学物质会对环境造成危害。另一方面，物理方法通常不会导致污染加剧，但从长远来看，它们不是很有效。我和我的团队最近开发的技术（周期性进料压力技术，PFPT）是新颖的，因为它不使用化学物质，从长远来看是有效的。它是基于膜细胞进料侧的压力在跨膜压力（TMP）和零之间循环交替，同时保持交叉流的运行。在一半的循环中，当膜上的压差等于TMP时，进行过滤；在后半程中，当压力为零时，通过交叉流场进行清洗。对这种技术的有效性进行了三项研究，结果非常有希望。在第一项研究中，采用多连续体建模方法来研究PFPT的性能。通过这项研究发现，确实在压力循环的后半段，保持在膜表面的材料失去了将它们粘在膜表面的阻力。第二项研究结合了计算流体动力学（CFD）工具，在微观尺度上研究了当TMP设置为零时油滴在膜表面的钉住行为。在最后一项研究中，建立了一个实验装置来研究使用常规过滤过程和新开发的PFPT的污染发展，以提供概念证明。研究结果非常令人鼓舞，已经完成了两份手稿，其中一份已发表在《水研究》（该领域的顶级期刊）上，第二份目前正在考虑中。通过NSERC的发现资助，该技术的发展可以通过优化进料周期和扩大PFPT在不同类型膜上的应用而达到另一个实现水平。

The decline of membrane performance due to fouling costs millions of dollars every year in process cleaning and rehabilitation. The disposal of fouled membranes once they become obsolete can lead to shutting off processes or bypass to a new line. Unfortunately, the decline in permeation flux due to fouling occurs within a relatively shorter period of time, which makes it difficult to frequently replace fouled units. A sustainable system, therefore, requires a longer time of operation for membranes to allow for easy manipulation of fouled ones. Therefore, inventing techniques to eliminate and minimize the problem of fouling is beneficial to the membrane industry, filtration technology and ultimately to the environment. Different methods to clean fouled membranes have been utilized and can generally be classified into chemical and physical-based techniques. Chemical methods use various chemicals to dissolve accumulated materials or to change the affinity properties of the membrane surface. Such chemicals, however, can pose hazard to the environment. Physical methods, on the other hand, do not generally lead to pollution intensification but they are not very effective in the long run. The technique that my team and I have recently developed (periodic feed pressure technique, PFPT) is novel in the sense that it utilizes no chemicals and is effective in the long run. It is based on alternating the pressure in the feed side of the membrane cell between the transmembrane pressure (TMP) and zero in cyclic manner while keeping the crossflow running. During half the cycle when the pressure difference across the membrane is equal to TMP, filtration occurs and during the second half when the pressure is zero, cleaning occurs by the crossflow field. Three studies on the effectiveness of this technique have been conducted with very promising results. In the first study, the multicontinuum modeling approach is used to investigate the performance of the PFPT. Through this study it was found that, indeed during the second half of the pressure cycle, the materials held at the surface of the membrane lost the drag force that stick them to the surface of the membrane. The second study incorporated the tools of computational fluid dynamics (CFD) to investigate, at a microscopic scale, the behavior of oil droplet pinning at the surface of the membrane when the TMP was set to zero. In the last study, an experimental setup was built to investigate the development of fouling using both regular filtration process and the newly developed PFPT to provide a proof of concept. The results are very encouraging and two manuscripts have been developed one of which has been published in Water Research (the top journal in the field) and the second is currently under consideration. Through the NSERC discovery grant, the development of this technique can reach another level of realization by optimizing the feed cycle and expanding the use of PFPT to different kinds of membranes.