Impact of 3D printed sinusoidal spacers on reverse osmosis

Abstract

Global water scarcity has been rapidly increasing. Desalination, a process which purifies seawater into potable water, has been gaining attention in an attempt to address this issue. Desalination uses Reverse Osmosis (RO) membranes to achieve high water purity for industrial or human consumption. RO membranes can be placed into Spiral Wound Modules (SWM) configurations which are most commonly used in the water treatment industry due to its high packing density. This paper focuses on optimising the feed spacer layer within the SWM in attempt to mitigate the fouling process on the membranes. 3D printing was adopted to fabricate the conventional and sinusoidal spacers. A series of tests were conducted to investigate the performance of the spacers. Mass Transfer and Pressure Drop (MTPD) tests were carried out with 2000ppm NaCl to find Sherwood number and Power number. The Sherwood number for the conventional spacer is approximately 70% higher compared to the sinusoidal spacers. The power number of the conventional spacer is 50% lower compared to the straight sinusoidal spacer and 150 to 300% lower compared to the slanted sinusoidal spacer. The straight sinusoidal spacer has 50% to 130% lower power number than that of the slanted sinusoidal spacer. Sodium Alginate was added as a component to simulate fouling, and methylene blue was added as a dye for easy visualization of the fouling cake layer formed on the spacer. Interestingly, the intensity of the dyed foulant shows that the conventional spacer seems to have fouled more in comparison to the sinusoidal spacers. This is supported by the greater flux decline for the conventional spacers compared to the sinusoidal spacers. After fouling, forward flushing was carried out as a cleaning process to determine the recovery effect of the spacers. Flux recovery was also higher in the sinusoidal spacers as compared to the conventional mesh spacer.