Technical guide: Index fouling procedures

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The Fouling Index (FI) is considered to be the most classic indicator in the field of membrane filtration. This index is used to define and quantify the clogging power of water with respect to a membrane. It is equivalent to the SDI (Silt Density Index) test, developed by the ASTM (American Society for Testing and Materials) under reference ASTM D4189-07. It is also known as the Sludge Density Index.

The determination is based on measuring the rate at which a cellulose acetate membrane with a pore diameter of 0.45 µm clogs during continuous filtration at a constant pressure of 2.1 bar.