Now showing 1 - 3 of 3
  • Publication
    Bacterial adhesion onto nanofiltration and reverse osmosis membranes: Effect of permeate flux
    The influence of permeate flux on bacterial adhesion to NF and RO membranes was examined using two model Pseudomonas species, namely Pseudomonas fluorescens and Pseudomonas putida. To better understand the initial biofouling profile during NF/RO processes, deposition experiments were conducted in cross flow under permeate flux varying from 0.5 up to 120 L/(h m2), using six NF and RO membranes each having different surface properties. All experiments were performed at a Reynolds number of 579. Complementary adhesion experiments were performed using Pseudomonas cells grown to early-, mid- and late-exponential growth phases to evaluate the effect of bacterial cell surface properties during cell adhesion under permeate flux conditions. Results from this study show that initial bacterial adhesion is strongly dependent on the permeate flux conditions, where increased adhesion was obtained with increased permeate flux, until a maximum of 40% coverage was reached. Membrane surface properties or bacterial growth stages was further found to have little impact on bacterial adhesion to NF and RO membrane surfaces under the conditions tested. These results emphasise the importance of conducting adhesion and biofouling experiments under realistic permeate flux conditions, and raises questions about the efficacy of the methods for the evaluation of antifouling membranes in which bacterial adhesion is commonly assessed under zero-flux or low flux conditions, unrepresentative of full-scale NF/RO processes.
      488Scopus© Citations 20
  • Publication
    Nanofiltration and reverse osmosis surface topographical heterogeneities: do they matter for initial bacterial adhesion?
    The role of the physicochemical and surface properties of NF/RO membranes influencing bacterial adhesion has been widely studied. However, there exists a poor understanding of the potential role membrane topographical heterogeneities can have on bacterial adhesion. Heterogeneities on material surfaces have been shown to influence bacterial adhesion and biofilm development. The purpose of this study was therefore to investigate whether the presence of membrane topographical heterogeneities had a significant role during bacterial adhesion as this could significantly impact on how biofouling develops on membranes during NF/RO operation. An extensive study was devised in which surface topographical heterogeneities from two commercial membranes, NF270 and BW30, were assessed for their role in the adhesion of two model organisms of different geometrical shapes, Pseudomonas fluorescens and Staphylococcus epidermidis. The influence of cross-flow velocity and permeate flux was also tested, as well as the angle to which bacteria adhered compared to the flow direction. Bacterial adhesion onto the membranes and in their surface topographical heterogeneities was assessed using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), fluorescence microscopy and image analysis. Results showed that up to 30% of total adhered cells were found in membrane defect areas when defect areas only covered up to 13% of the membrane surface area. This suggests that topographical heterogeneities may play a significant role in establishing environmental niches during the early stages of biofilm development. Furthermore, no noticeable difference between the angle of cell attachment in defect areas compared to the rest of the membrane surface was found.
      384Scopus© Citations 16
  • Publication
    The role of cell-surface interactions in bacterial initial adhesion and consequent biofilm formation on nanofiltration/reverse osmosis membranes
    Until recently, the realization that membrane biofouling during nanofiltration (NF) and reverse osmosis (RO) processes is an unavoidable occurrence, has led to a paradigm shift in which biofouling management approaches rather than biofouling prevention are now being considered. To implement this new concept, it is crucial to understand the fundamentals of cell-surface interactions during bacterial adhesion, a prerequisite to biofouling of membranes. As such, with membrane biofouling already being widely studied and documented, greater attention should be given to the factors involved in the initial bioadhesion onto membranes during NF/RO processes. This review focuses on the interactions between bacterial cells and NF/RO membranes, emphasizing the mechanisms of bacterial adhesion to NF/RO membranes with particular reference to the effects of micro-environmental conditions experienced at the membrane interface, such as feed-water composition, hydrodynamics, permeate flux and conditioning layers. This review also discusses membrane surface properties and how it relates to bacterial adhesion as well as latest advancements in antibacterial membranes, identifying areas that need further investigation.
      1212Scopus© Citations 193