Abstract
In this study, the mechanical properties of biofilms formed at the surface of nano-filtration (NF) membranes from a drinking water plant were analysed. Confocal laser scanning microscopy observations revealed that the NF biofilms formed a dense and heterogeneous structure at the membrane surface, with a mean thickness of 32.5 ± 17.7 μm. The biofilms were scraped from the membrane surface and analysed in rotation and oscillation experiments with a RheoStress 150 rotating disk rheometer. During rotation analyses, a viscosity decrease with speed of shearing characteristic of rheofluidification was observed (η = 300 Pa s for ý = 0.3 s−1). In the oscillation analyses with a sweeping of frequency (1–100 Hz), elasticity (G′) ranged from 3000 to 3500 Pa and viscosity (G″) from 800 to 1200 Pa. Creep curves obtained with an application of a shear stress of 30 Pa were viscoelastic in nature. The G 0 and η values were, respectively, 1.4 ± 0.3 × 103 Pa and 3.3 ± 0.65 × 106 Pa s. The relationship between the characteristics of NF biofilms and the flow conditions encountered during NF is discussed.
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