Facile Membrane Surface Activation Eliminates Fouling on Demand and Mitigates Concentration Polarization

Fouling of high pressure membranes is a recalcitratnt problem, particularly in reverse osmosis (RO) and nanofiltration (NF) systems. Colloidal, organic and biological fouling are the most commonly encountered challenges in industrial desalination and wastewater treatment processes and there is no convenient way to clean the membrane without interrupting operation or resorting to expensive fouling mitigation infrastructure. Therefore, significant energy savings can be achieved by real time fouling elimination and concentration polarization mitigation. Although several important technological improvements were achieved in membrane design and fouling control in past few years, for example-  TiO₂ embedded composite antifouling membranes, photothermal nanoheater membranes or carbon nanotube containing composite electrolytic membranes, which are promising in reducing different types of fouling. However, all the reported methodologies suffer from requiring extensive new infrastructure, lack of scalability and most importantly, efficiency without loss in productivity.

 

Here, we have demonstrated a simple scalable approach of coating RO/ NF membrane with bioinspired adhesive polymer polydopamine and copper oxide nanoparticles, which decomposed H₂O₂ (0.006% - 0.024%) to oxygen bubbles and thereby, swept foulants away from the surface and at the same time reduced concentration polarization by enhancing mass transfer co-efficient. The polydopamine layer embedded the nanoparticles and acted as the reactive catalytic surface. Additionally, polydopamine layer helped to protect the underlying polyamide layer from hydroxyl radicals by acting as free radical scavenger. Such composite membrane eliminated flux decline with colloidal foulants in repeated runs and even increased the flux level beyond the baseline value with organic humic acid foulants. Enhanced catalytic activity of humic acids in presence of H₂O₂ and reduction of concentration polarization were found to be responsible for such flux enhancements. Embedded copper oxide nanoparticles also retarded E. Coli attachment to the membrane surface in stirred cell experiments. On the other hand, such composite membrane was found to eliminate concentration polarization upon H₂O₂ addition by bubble induced mixing. Therefore, such scalable facile approach holds promise to mitigate fouling in industrial membrane systems, reduce concentration polarization and thereby, saving considerable energy.

Figure. SEM micrograph of rod shaped CuO nanoparticles on polydopamine coated RO membrane. In the inset, TEM micrograph of petal shaped CuO nanorods.