Use of ionic strength responsive polymeric microgels for fouling removal in membrane filtration

Çalılı, Fatma
Stimuli-responsive polymeric surfaces can improve non-fouling properties of membranes and control their pore size and permeation characteristics upon alteration of stimulus intensity. In this study, zwitterionic poly(sulfobetaine methacrylate) (P(SBMA)) microgels have been added into the feed or deposited on the membrane surfaces to clean foulant deposits formed on the surface of the membranes after the filtration. Salt-responsive P(SBMA) microgels have altered their phase from swollen to shrunk, swollen to more swollen or shrunk to swollen due to the change of ionic strength in the medium. The effect of this size change in loosening and removing the fouling layer on the membrane was investigated. In the performance tests, PES (polyether sulfone) based ultrafiltration membranes were used. P(SBMA) microgels used in the tests as the ionic strength responsive microgel were synthesized by inverse emulsion free-radical polymerization. Fouling resistances and flux recoveries of membranes were calculated using pure water permeances (PWP) of neat membranes, filtration fluxes and PWP of the membranes after applying the cleaning procedure to compare their cleaning efficiencies. Different foulants, which are Bovine serum albumin (BSA), humic acid in the presence of calcium ions (HA gel) and yeast cells, were used with or without the zwitterionic microgels in the presence of different sodium chloride (NaCl) concentrations. To remove the cake layer, cleaning was performed via stirring and pure water/salt solution to make them shrink/swell. P(SBMA) microgels can maximally swell in the presence of 0.5 M NaCl. Due to the formation of highly adsorptive fouling, the microgels could not provide an efficient BSA fouling removal. HA gel fouling in the absence of NaCl was the most irreversible while when NaCl was in the feed, reversibility was similar with or without microgel. This possibly implies a looser cake layer in the presence of NaCl. Yeast fouling, however, was more reversible when P(SBMA) microgels were used, compared to fouling with yeast in pure water or in 0.5 M NaCl. In conclusion, this study showed how P(SBMA) microgels affect cake layer removal from PES UF membrane surface by adding them in the feed or depositing them on the membrane surface before the filtration. Presence of P(SBMA) microgels in the solution medium during the filtration could render higher flux recovery and cleaning efficiency than microgel-free filtrations for all foulants. Particularly, yeast fouling removal was achieved by adding of these microgels into the feed and depositing them on the membrane surface. These promising physical methods can be applicable to existing membrane processes to remove yeas-like foulants.
Citation Formats
F. Çalılı, “Use of ionic strength responsive polymeric microgels for fouling removal in membrane filtration,” M.S. - Master of Science, Middle East Technical University, 2019.