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What is the SDI?

April 26, 2017SDI

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What is the SDI?

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The best available technology for determining the colloidal fouling potential of reverse osmosis feed water is the measurement of Silt Density Index (SDI). This is an important measurement to be carried out prior to designing an RO pretreatment system and on a regular basis during RO operation (2-3 times a day is recommended for surface waters). The Standard Test Method has been described in ASTM test D 4189-82. The guideline is to maintain SDI at less than or equal to 5. A number of pretreatment technologies have proven effective in SDI reduction including media filtration, ultrafiltration, and cross flow microfiltration. Polyelectrolyte addition ahead of filtration sometimes improves SDI reduction.