(700c) Cellulose Acetate Ultrafiltration Membranes Modified with Temperature-Sensitive Polymers for Fouling Resistance

The presence of microorganisms in feed water can exacerbate fouling due to the accumulation of microorganisms onto the membrane surface and on the feed spacer between the envelopes, or biofouling. Microorganisms transported to the membrane element can attach to the feed side of the membrane and the spacer. Attachment depends on Van der Waals forces, hydrophobic interactions and electrostatic interactions between the microorganisms and the surface. Biofouling control has been attempted via biocide additions; however, while a biocide may kill the biofilm organisms, it usually does not remove the biofouling layer, and may cause bacteria that survive disinfection to potentially become more resistant.

The goal of this study was to produce a fouling-resistant membrane by attaching a stimuli-responsive polymer on the membrane surface, which collapsed or expanded as a response to the stimulus. The phase change arises from the existence of a lower critical solution temperature (LCST) such that the polymer precipitates from solution as the temperature is increased. The polymers studied for this application were hydroxypropyl cellulose and N-isopropylacrylamide, which have LCSTs of 46 C and 32 C, respectively.

Roughness measurements, using a wet atomic force microscopy (AFM) cell, and filtration experiments (to monitor flux declines) were performed at cold temperatures (25oC), at hot temperatures (60oC) and with temperature oscillations. The unmodified membrane roughness values were unaffected by temperature changes, and it displayed flux declines under all temperature conditions. When the modified membranes were tested, both roughness values and filtration experiments supported temperature activation.

Developing a membrane with high flux and selectivity along with low fouling is one of the goals of membrane research. There are physical and chemical limitations, however, that cannot be disregarded. For microfiltration/ultrafiltration systems higher flux operation requires energy input, in the form of back flushes, air scouring, physical agitation, etc, to reduce fouling. The work presented here developed a membrane with desired inherent properties along with fouling control.