Biofouling formation and structure on original and modified PVDF membranes: Role of microbial species and membrane properties

In our previous study, three types of modified PVDF membranes, PVDF-g-PHEMA, PVDF-g-PNIPAAm, and PVDF-g-P(HEMA-co-NIPAAm), were successfully prepared by grafting the functional polymers PHEMA and PNIPAAm. In this study, bacterial adhesion tests on the original and modified PVDF membranes were performed using two model microbial species, i.e. Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis, to investigate the effect of microbial species and membrane properties on the formation and structure of biofouling. The results indicated that less biofouling was found on the modified membranes as compared to that on the original membrane in both mono-species tests and mixed-species tests; this finding confirmed that the hydrophilicity of the membrane significantly affected the formation of biofouling such that the antifouling properties of the PVDF membranes were remarkably enhanced after grafting of the hydrophilic polymers on them. Less biofouling was observed on the modified hydrophilic membranes, with scattered biofouling spots for mono-species, whereas a thin layer structure of biofouling was observed for mixed-species; however, heavy biofouling covered the original membrane with a thick cake layer for both mono-species and mixed-species. This demonstrated that the microbial species significantly affected the formation and structure of biofilms since the species influenced the bacterial adhesion and biofouling behavior of each other based on their type and characteristics; moreover, the hydrophilicity of membrane also displayed an essential effect on the biofouling structure. The novelty of this study is as follows: it demonstrates that the microbial species and membrane properties play an essential role in the biofouling formation and structure as well as how to influence biofouling on different membranes; this study can provide useful insight and indications on how to effectively control and inhibit biofouling in the future.