Co-Deposition of Stimuli-Responsive Microgels with Foulants During Ultrafiltration as a Fouling Removal Strategy

In this study, we show that codeposition of temperature responsive microgels in the foulant cake layer and cleaning of the cake upon stimuli-induced size change of the microgels is an effective method of fouling removal. Humic acid in CaCl2 solution was used as a model foulant and poly(n-isopropylacrylamide) (p(NIPAm)) and poly(n-isopropylacrylamide-cosulfobetainemethacrylate) (p(NIPAm-co-SBMA)) were used as temperature responsive microgels. Filtrations were done below the lower critical solution temperature (LCST) and temperature was increased to above the LCST for cleaning. As an extra cleaning a temperature swing of above, below and then again above the LCST was applied. P(NIPAm) was found to be ineffective in cleaning the foulant deposit despite the 20-fold change in its volume with temperature change at LCST. P(NIPAm-co-SBMA) microgels, on the other hand, provided high fouling reversibility on hydrophilic poly(ether sulfone)(PES)/poly(vinylpyrrolidone) (PVP) and hydrophobic PES membranes. Better fouling reversibility with these microgels was observed at low and high solution ionic strength. While the use of microgels alone increased fouling reversibility to some extent, even in the absence of temperature stimulus, 100% reversibility could only be obtained when a temperature switch was applied in the presence of microgels, showing the effect of microgels' volume change in cleaning.