(499c) 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.