(424b) Hybrid Chitosan/Poly(Ethylene Glycol) Hydrogels for Use as Highly Anti-Fouling Ultrafiltration Membrane Coatings for Synthetic Oily Water Treatment

Membrane technology provides an attractive solution to wastewater treatment based on their relative versatility, small environmental and spatial footprint, and inherent economic advantages over other alternatives. However, the largest barrier to widespread use of water purification membranes is fouling, which is the deposition of matter in a membrane's pores (internal fouling) or on its surface (external fouling) that leads to a change in a membrane's flux characteristics, such as throughput and selectivity. Many different techniques can be used to combat membrane fouling, most of which focus on two general areas: introducing fluid instabilities in the feed stream, such as dean vortices, air sparging, and backflushing, and altering the surface properties of the membranes, either through surface grafting or coating. Although feed flow instabilities have been shown to increase flux in some MF and UF membrane applications, fouling is still a major concern, especially when internal fouling is the dominant fouling mechanism. Therefore, coating a thin, defect-free hydrophilic polymer on the surface of a porous membrane (which is usually made of a hydrophobic polymer) may provide the most effective way to eliminate internal membrane fouling while greatly reducing external fouling. A hydrophilic polymer coating, when made sufficiently thin, can also allow a high water throughput to maximize flux.

Here, we report the synthesis of a series of novel hydrophilic coating materials prepared by crosslinking chitosan with a bifunctional poly(ethylene glycol) macromer. The water permeability and chemical stability of these polymers have been found to be satisfactory for application as a potential membrane coating. Furthermore, the molecular weight cutoff (MWCO) using poly(ethylene glycol) feed solutions was found to be as low as 720 for these polymers, and generally varied inversely to the film's water permeability. The low MWCO indicates that high rejection can be expected for most organic contaminants, including emulsified oil droplets and most proteins. From a practical point of view, members of this polymer series were coated onto commercially-available polysulfone membranes to investigate anti-fouling characteristics using synthetic oily water. These composite membranes exhibited water flux values more than 3 times higher than uncoated membranes after one day of oily-water crossflow filtration, indicating that the hydrophilic polymer coating can significantly enhance anti-fouling properties. The organic rejection of the coated membranes was also higher than that of the unmodified polysulfone membranes.