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Microbial biofilms and their components present a major obstacle for ensuring the long-term effectiveness of membrane processes. Graft polymerization on membrane surfaces, in general, and grafting with oppositely charged monomers, have been shown to reduce biofouling significantly. In this study, surface forces and macromolecular properties of graft copolymers that possess oppositely charged groups were related to their potent antibiofouling behavior. Graft polymerization was performed using the negatively charged 3-sulphopropyl methacrylate (SPM) and positively charged [2-(methacryloyloxy)ethyl]-trimethylammonium (MOETMA) monomers to yield a copolymer layer on polyvinylidene fluoride (PVDF) surface. Quartz crystal microbalance with dissipation monitoring (QCM-D) technology was used to monitor the reduced adsorption of extracellular polymeric substances (EPS) extracted from a membrane bioreactor (MBR) wastewater treatment facility. Complemented measurements of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy provided evaluation of the antifouling properties of the surface. Increase in water content in grafted layer exposed to 100 mM aqueous NaCl solution was observed by QCM-D. Therefore, the grafted copolymer layer is swelled in the presence of 100 mM NaCl because of reversing of polymer self-association by counterions. Force measurements by atomic force microscopy (AFM) showed an increased repulsion between a carboxylate-modified latex (CML) particle probe and a modified PVDF surface, especially in the presence of 100 mM NaCl. The hydration and swelling of the grafted polymer layer are shown to repel EPS and reduce their adsorption. Delineating the surface properties of antifouling grafted layers may lead to the design of novel antifouling surfaces.

Laboratory-scale reverse osmosis (RO) flat-sheet systems were used with two parallel flow cells, one treated with cleaning agents and a control (ie undisturbed). The cleaning efforts increased the affinity of extracellular polymeric substances (EPS) to the RO membrane and altered the biofilm surface structure. Analysis of the membrane biofilm community composition revealed the dominance of Proteobacteria. However, within the phylum Proteobacteria, γ-Proteobacteria dominated the cleaned membrane biofilm, while β-Proteobacteria dominated the control biofilm. The composition of the fungal phyla was also altered by cleaning, with enhancement of Ascomycota and suppression of Basidiomycota. The results suggest that repeated cleaning cycles select for microbial groups that strongly attach to the RO membrane surface by producing rigid and adhesive EPS that hampers membrane performance.

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