Quantification of Bacterial Adhesion and Characterization of Polymeric Pristine and Modified UF Membranes

Membrane filtration is an important technology that might help solving future challenges regarding the access to potable drinking water. One of the main challenges in membrane operations is biofouling. Biofouling is the formation of a biofilm on the membrane surface. It deteriorates the system performance, leads to higher operating pressure and a reduced life of the membrane (Ridgway and Flemming, 1996). Bacteria accumulate on surfaces by adhesion and growth, feeding on easily assimilable organics present in the feed stream (Machenbach, 2007). In order to make this technology more accessible and cost-efficient, an optimization is necessary. Membrane surface modification can reduce fouling by altering the surface properties and weakening the membrane-foulant interactions. In this study, the efficiency of polydopamine (PDA) as an anti-foulant was studied. PDA is naturally found in mussels and is a result of the oxidization of dopamine (Lee et al., 2007). Polysulfone (PSF) ultrafiltration (UF) membranes were fabricated using wet phaseinversion process and coated with 4g/L PDA. The membranes were characterized both before (PSF) and after coating (PSF-PDA). The hydrophobocity, permeability and roughness were determined using contact angle measurements, finding the pure water flux and Atomic Force Microscopy (AFM) respectively. The bacterial adhesion was then quantified using AFM and single cell force spectroscopy (SCFS). A single P.fluorescens was immobilized on a PDA-coated cantilever and measurements were taken over both membrane types. The applied force was 600 pN for all the curves, and the contact time varied between 0s, 2s and 5s. The hydrophilicity increased significantly when coating. Not only does this have a positive effect on the reduction of bacterial adhesion, but it also might have contributed in increasing the permeability. The roughness did not increase much, but when scanning over larger areas, some nanoaggregates could be observed. The obtained force curves showed that the force of adhesion (Fadh) increased with an vi increasing contact time. The contact time did not have a statistical significant impact on the rupture length (Lrup), one can therefore conclude that bond strengthening does not involve a sequence of different adhesins, but rather an increasing number of adhesins increasing the interaction. The adhesion force decreased drastically when obtained on modified membranes. These results are promising in regards of using PDA as an anti-foulant on UF membranes. However, the tests were performed under highly simplified conditions and the coating should be subject to further testing