Silt Density Index (SDI) Kit

SDI measurement is one of the best methods for monitoring the performance of pretreatment equipment relative to the potential for downstream membrane fouling.

The rate at which 500 mL of water passes through a 0.45 micron filter at a pressure differential of 30 psi is measured initially and after a time interval of 5, 10, or 15 minutes.  The SDI index is calculated as the ratio of these measured times subtracted from one, multiplied by 100 and divided by the total time of the test in minutes.

Because the 0.45 micron filter is tight enough to remove bacteria and most of their byproducts, the SDI test results tend to better correlate with the performance of a membrane system than turbidity and other non-membrane based analyses.