|M.Sc Student||Sofia Lerman Roytblat|
|Subject||Slippery, Liquid-Infused Feed Spacers for Biofouling|
Control in Membrane Systems
|Department||Department of Civil and Environmental Engineering||Supervisor||Assistant Professor Ramon Guy|
|Full Thesis text|
The water crisis is one of the biggest concerns in the 21th century. A promising solution is seawater desalination using membrane separation systems. While membranes have many advantages, e.g. they are efficient and relatively cheap, they can suffer from fouling, particularly biofouling-accumulation of bacteria on the membrane. Biofouling decreases the permeate flux and increases the energy consumption. A new approach for biofouling control is feed spacer modifications, with research focused on adding biocidal properties to the spacer. Herein, we demonstrate a different approach, by changing the surface of the spacer, covering it with a liquid-like layer. Due to its ‘slipperiness’, bacteria would have difficulty attaching to the spacer and biofouling will be reduced. For this purpose, we fabricated a spacer with a slippery, liquid-infused surface (SLIPS) coating, which consists of a substrate attached to a lubricant -fluorinated oil - that provides the slippery effect. After coating, we characterized them using FTIR (Fourier transform infrared) spectroscopy, Raman spectroscopy, a visual sliding drop test and QCM-D (Quartz-Crystal Microbalance with dissipation). The FTIR showed a new peak that matched a Carbon-Fluorine bond and gave us an indication that we succeeded to coat the surfaces. The sliding droplet test also gave us a visual proof to the successful coating. Raman spectroscopy, enabling larger areas to be scanned, showed the coating was patchy. The Carbon-Fluorine peak didn’t appear in the entire area- some parts had more coating and some less. QCM-d provides the mass of the coating layer, from which an estimate of the thickness can be made. The QCM results showed a high variance in the thickness of the coating - from 10 nm to almost 1 µm. The SLIPS spacers were tested for their antifouling properties in a microfluidic flow system under two shear rates with a wash at the end of each experiment. Each flow cell was scanned using a confocal microscope. The accumulated bacteria on the SLIPS spacers was significantly smaller than on the control spacers for both shear rates. The results of the image analysis were submitted to a two-sample T-test and the results confirmed the visual observation with a p.value=0.0277 for ý=0.068 [s-1] and a p.value=0.0014 for ý=0.2 [s-1]. The higher shear rate had less bacteria on the SLIPS spacers because the shear is one of the mechanisms preventing the adhesion of the bacteria. The amount of the EPS accumulated was the same for both the control spacer and the SLIPS spacer (p.value=0.7371 for ý=0.068 [s-1] and a p.value=0.1433 for ý=0.2 [s-1] . The wash that was performed at the end of each experiment didn’t have a significant effect on the bacteria and EPS removed from the spacers with p.value>0.05 for both parameters. Overall the SLIPS spacers showed the ability to reduce biofouling formation and with further research they have the potential to be integrated in spiral wound modules to control biofouling formation. Further research should include improving the uniformity of the coating and testing the SLIPS spacers with membranes to see if the SLIPS spacers can reduce biofouling on the membrane.