Fouling control using temperature responsive N-isopropylacrylamide (NIPAAm) membranes

Membrane fouling occurs when there is reversible or irreversible accumulation of macrosolutes present in the water on the membrane surface or within the pores. Membrane cleaning and eventual replacement due to fouling can add to the operational costs of membrane systems. Reversible fouling can be minimized by crossflow operation and/or backflushing. On the other hand, irreversible fouling cannot be minimized during operation, often requires chemical cleaning, and may result in permanent flux decline. Among irreversible foulants, natural organic matter (NOM) is considered to be a major contributor. NOM is composed of a wide range of hydrophilic and hydrophobic components; hence, any stagnant hydrophobic or hydrophilic membrane has the potential to become fouled. Therefore, a dynamic membrane able to alternate between being hydrophobic and hydrophilic was proposed to foul less. The purpose of this study was to cast low fouling stimuli-responsive membranes made of cellulose acetate (CA) and N-isopropylacrylamide (NIPAAm). NIPAAm is a stimuli-responsive polymer, which offers the potential to reversibly collapse or expand the membrane as a function of changes in temperature. Membranes were cast using phase inversion, were characterized chemically and morphologically, and were used to filter bovine serum albumin (BSA), lipase and humic acid. Flux studies were conducted at alternating cold and hot temperature cycles. CA-NIPAAm membranes displayed on average higher fluxes during operation and lower protein and humic accumulation on their surfaces as compared to regular CA membranes. CA-NIPAAm membranes also showed higher flux recoveries as compared to CA membranes.