Abstract
Membrane separation processes including reverse osmosis are now considered essential techniques for water and wastewater treatment, especially in water-scarce areas where desalination and water reuse can augment the water supply. However, biofouling remains a significant challenge for these processes and in general for marine biological fouling, which results in increased energy consumption and high operational costs. Especially in flat sheet membrane modules, intense biofilm growth occurs on the feed spacer at points of contact to the membrane surface. Here, we developed an ultrastable superhydrophobic antibiofouling feed spacer that resists biofilm growth. A commercial polypropylene feed spacer was coated with poly(dimethylsiloxane) (PDMS), and then, candle soot nanoparticles (CSNPs) were embedded into the ultrathin layer of PDMS, which resulted in a superhydrophobic nanostructured surface with a contact angle >150°. The CSNP-coated spacer was examined for inhibition of biofilm growth by a cross-flow membrane channel using Pseudomonas aeruginosa (PA01), and the coating was examined for effectiveness in marine fouling by testing the adhesion of marine bacterium Cobetia marina and diatom Navicula perminuta in a dynamic accumulation assay. In all cases, the CSNP coatings showed almost complete elimination of biofilm growth under the conditions tested. Confocal laser scanning microscopy and scanning electron microscopy indicated a 99% reduction in biofilm growth on the modified spacers compared to the uncoated controls. This effect was attributed to the superhydrophobic nanostructured surface, where trapped gasses formed a plastron on the coating. This plastron was observed to be extremely stable over time and could even be replenished at elevated temperatures. Development of similar antibiofouling coatings on feed spacers or other marine applications might lead to improvements in many industrial processes including membrane filtration where increased membrane life span and reduced energy consumption are key to implementation.
Highlights
Desalination using reverse osmosis (RO) and nanofiltration (NF) technologies is increasingly used globally due to water scarcity
Candle soot coatings have been shown to possess unique properties including superhydrophobicity.[21,37−39] Candle soot was embedded onto the surface of PP feed spacers by first coating with a diluted uncured PDMS layer estimated to be ∼20 to 30 μm and moving the spacer through the middle of a candle flame
Our findings demonstrate that CSNPcoated spacers would be beneficial for biofouling control on commercial feed spacers. 3.3
Summary
Desalination using reverse osmosis (RO) and nanofiltration (NF) technologies is increasingly used globally due to water scarcity. Eliminating the pretreatment stage or reducing the pretreatment demands would substantially reduce the energy consumption, capital cost, and environmental impact of desalination plants, but this requires the development of fouling-resistant membranes with tailored surface properties, as well as membrane modules with improved hydrodynamic mixing.[1] Many of the applications use membranes in a spiral-wound configuration that contains a feed spacer, which creates an intermembrane space but can affect mixing and enhance mass transfer in membrane systems.[2] the feed spacer material and mesh structure lead to inevitable biofilm growth on the feed spacer and can cause a strongly negative impact on membrane and system performance.[3,4] the control and prediction of fouling due to microorganisms are serious challenges in membrane filtration processes and on surfaces in the marine environment, which novel coatings might address
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