Membrane Foulants Characterization in a Drinking Water Production Unit

We characterized the composition and organization of membrane foulants in a French drinking water production plant between March and September 2005 by the combination of Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy, lectin-binding analysis, epifluorescence microscopy and Confocal Laser Scanning Microscopy (CLSM). The comparison of ATR-FTIR spectra of clean and fouled membranes revealed a qualitatively homogenous deposition of biological matter onto the membrane surface, a high heterogeneity in the composition of the fouling material and a high temporal stability of this composition. Characteristic signals of mainly polysaccharides (900–1200 cm −1) and proteins (1300–1700 cm −1) were observed. Fluorescence microscopy observations after nucleic acid staining with DAPI and polysaccharides staining with lectins labelled with fluorescein isothiocyanate or tetramethylrhodamine isothiocyanate indicated a high spatial heterogeneity inside the foulant matter. The microbial cells, mainly composed of bacteria, were localized in the superficial layer of the fouling material and were organized as microcolonies interspersed at the membrane surface. Polysaccharide residues were found in areas where microcolonies were present and in areas devoid of microbial cells. High staining with Peanut and Bandeiraea simplicifolia agglutinins (PNA, BS-1, respectively) revealed high occurrence of galactosides residues in the polysaccharide components of the foulants. The BS-1 lectin staining pattern indicated a high degree of spatial organization with the observation of long and entangled fibres. Wheat germ agglutinin staining showed short fibres and cloud stained areas. PNA and Concanavalin A lectin staining were more interspersed. In conclusion, the combination of ATR-FTIR spectroscopy with lectin-binding analysis was a very informative tool for the characterization (composition and spatial organization) of the foulants that cover the surface of the membranes.