Surface Modification of Thin-Film Composite Reverse Osmosis Membranes With Copper Nanoparticles for Biofouling Mitigation

Nanomaterials, such as silver nanoparticles (NPs), zinc-NPs, titanium-oxide-NPs, and carbon nanotubes, have been explored for use as biocidal materials in membrane processes, each with varying degrees of success. However, the effectiveness of copper nanoparticles (Cu-NPs) as biofouling mitigation agents has not been investigated previously in membrane processes. Copper has long history as a highly efficient anti-microbial agent. It is relatively cheap (less than 1% the cost of silver), and it is a vital nutrient, which implies a relatively low potential environmental hazard at low concentrations. Therefore, there is a need to investigate the use of Cu-NPs as potential biocides in membrane processes.

In the current work, we developed a simple protocol for the production of aquatic Cu-NPs using polyethylenimine (PEI) as a capping agent. The positively charged Cu-NPs were electrostatically bound to the native negatively charged carboxylic groups on the surface of seawater reverse osmosis membranes. We demonstrated that the successful binding of Cu-NPs did not significantly affect the membrane transport properties, and modified membranes maintained both high water permeability and salt rejection (>98.5% NaCl rejection). Membranes modified with Cu-NPs were shown to be highly toxic to several bacterial strains, with a 85-95% reduction in the number of live bacteria compared to the control. In addition, the model bacteria showed significant changes in cell morphology upon exposure to Cu-NPs, implying high cytotoxicity of the bound Cu-NPs.

Although the current work demonstrated the high potential of Cu-NPs as an efficient, low cost biocide for reverse osmosis membranes, several challenges have to be addressed before practical application. Such challenges include reducing the binding reaction time between the Cu-NPs and the membrane, increasing the amount of copper on the membrane, and controlling Cu-NPs dissolution rates. The objective of the current presentation is to elucidate both the potential and the challenges of Cu-NPs as a biocide in reverse osmosis desalination processes.