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

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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. ***********