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

由于膜污染导致的膜性能下降每年花费数百万美元用于过程清洗和修复。一旦污染的膜变得过时，对其进行处理可能会导致关闭工艺或旁路到新的生产线。不幸的是，由于结垢导致的渗透通量的下降发生在相对较短的时间段内，这使得难以频繁地更换结垢的单元。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，发明消除和最小化结垢问题的技术对膜工业、过滤技术以及最终对环境有益。已经使用了不同的方法来清洁污染的膜，并且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品来溶解积累的材料或改变膜表面的亲和性质。然而，这些化学品可能对环境造成危害。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，因为它不使用化学品，并且从长远来看是有效的。它是基于在保持交叉流运行的同时，以循环方式在跨膜压力（TMP）和零之间交替膜单元的进料侧中的压力。在半个循环期间，当跨膜的压差等于TMP时，发生过滤，并且在后半个循环期间，当压力为零时，通过交叉流场发生清洁。已经对这种技术的有效性进行了三项研究，取得了非常有希望的结果。在第一项研究中，多连续建模方法被用来调查的PFPT的性能。通过该研究发现，实际上在压力循环的后半部分期间，保持在膜表面处的材料失去了将它们粘附到膜表面的拖曳力。第二项研究结合了计算流体动力学（CFD）的工具，在微观尺度上研究当TMP设置为零时，油滴钉扎在膜表面的行为。在最后一项研究中，建立了一个实验装置，以调查污垢的发展，使用常规的过滤过程和新开发的PFPT提供一个概念的证明。结果非常令人鼓舞，已经编写了两份手稿，其中一份已发表在《水研究》（该领域的顶级期刊）上，另一份目前正在审议中。通过NSERC的发现资助，通过优化进料循环和将PFPT的使用扩展到不同类型的膜，该技术的开发可以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. ***********