Biofouling Response of Laboratory-Scale Polysulfone Membranes Modified with Bioinspired Polydopamine and Silver Nanoparticles

Low-pressure membranes provide high-quality water through physical removal of bacteria, cysts, and particles. Bacteria can attach to the membrane surface and form biofilms that reduce energy efficiency and increase the frequency of membrane replacement. Modifying membranes with polydopamine, a chemical mimic of the adhesive proteins that mussels release, has the potential to delay biofilm formation. Dopamine polymerizes under mild conditions, forming a coating that is of interest in membrane applications due to its hydrophilic and reactive nature. Compared with hydrophobic base membranes, hydrophilic surfaces are resistant to bacterial attachment. Additionally, when polydopamine is exposed to silver nitrate, a reduction reaction takes place that embeds antimicrobial silver nanoparticles into the polydopamine layer. This study paired short-term deposition experiments with longer-term filtration experiments to determine the efficacy of this modification when challenged with Pseudomonas aeruginosa. Modification with polydopamine resulted in an average 48% reduction in the initial deposition rate of P. aeruginosa. However, hydrophilicity of the polydopamine layer did not have a significant impact on membrane performance over 3 days of bacterial filtration. Only the combination of both polydopamine and silver nanoparticles improved the rate of water production, with an average flux 1.7 times greater than that of the unmodified membrane. Confocal microscopy revealed heterogeneous bacterial growth on all membrane types with a lack of association between membrane performance and biofilm structure. Modifying membranes with polydopamine and silver nanoparticles has the potential to ameliorate the effects of biofouling, thereby increasing the efficiency of membrane water treatment.