Responsive polymer particles for fouling removal during membrane filtrations

Aksoy, Canan
In this study, temperature and ionic-strength responsive polymeric microgels are used for fouling removal in membrane filtrations by adding them into feed solutions such that they deposit on the membrane surface together with the foulants during filtration. For removal of the fouling layer, the microgels in collapsed form are brought into swollen phase or vice versa by applying temperature change. Recently, in literature, there are several studies that stimuli-responsive surfaces have been shown to be effective in removing the fouling by “shaking off” the foulants from the membrane surface in response to appropriate stimuli. In the filtrations, PES (polyethersulfone) and PES/PVP (polyvinylpyrrolidone) blend membranes were used. It was observed that flux declined less with PVP addition than PES membrane owing to its hydrophilicity. Poly(N-isopropylacrylamide), p(NIPAm), and poly(N-isopropylacrylamide-co-sulfobetainemethacrylate), p(NIPAm-co-SBMA), microgels were synthesized by precipitation polymerization and used in the filtrations as responsive microgels. Pure water permeances (PWP) of clean membranes, filtration permeances and PWP of the used membranes after cleaning were compared in terms of flux recovery and fouling resistances. Bovine serum albumin (BSA) and humic acid (HA) were used as foulants in the presence and absence of microgels. For fouling removal, cleaning was done by stirring and simultaneously heating or cooling the filtration cell above or below lower critical solution temperature (LCST) depending on filtration condition, e.g. cleaning was done above LCST for the filtration performed below LCST in order to change size of the responsive microparticles. Thermo-responsive p(NIPAm) and p(NIPAm-co-SBMA) microgels used had swelling ratios of 2.9 and 2.1, and LCST of 32 and 29C, respectively. Addition of p(NIPAm-co-SBMA) microgel enabled less fouling resistance and more efficient cleaning compared to microgel-free cases for HA filtrations where the microgels were hydrophilic during filtration. In consequent filtrations, flux was almost completely recovered after HA filtrations for both PES and PES/PVP membranes either in pure water and in 0.5 M NaCl while flux recovery was around 60, 92 and 80% for PES membrane in pure water, PES/PVP blend one in pure water and 0.5 M NaCl, respectively. However, P(NIPAm) microgels did not provide better cleaning efficiency in neither BSA nor HA fouling for the filtrations above LCST where the microgels were hydrophobic.
Citation Formats
C. Aksoy, “Responsive polymer particles for fouling removal during membrane filtrations,” M.S. - Master of Science, Middle East Technical University, 2018.