Adhesion strength and spreading characteristics of EPS on membrane surfaces during lateral and central growth

Deposition of extracellular polymeric substances (EPS) on membrane surfaces is a precursor step for bacterial attachment. The purpose of this study was to analyze the morphological changes on a clean polysulfone ultrafilration membrane after exposure to effluent from a membrane bioreactor. The effluent was filtered to remove bacteria before exposing the membrane. The morphological characterization was performed by atomic force microscopy (AFM). The lateral (2D) and central growth characteristics (3D) of the EPS deposits were evaluated by section and topographical analyses of the height images. The contact angle of single EPS units was 9.07 ± 0.50° which increased to 24.41 ± 1.00° for large clusters (over 10 units) and decreased to 18.68 ± 1.00° for the multilayered clusters. The surface tension of the single EPS units was 49.34 ± 1.70 mN m−1. The surface tension of single layered small and large EPS clusters were 51.26 ± 2.05 and 53.48 ± 2.01 mN m−1, respectively. For the multilayered clusters, the surface tension was 51.43 ± 2.05 mN m−1. The spreading values were negative for all deposits on the polysulfone membrane indicating that the EPS clusters did not have tendency to spread but preferred to retain their shapes.