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Product Number: 2195900
The Silt Density Index (SDI) test is used to estimate particulate contamination in water and is a widely accepted method for assessing the potential for colloidal and particulate fouling in water purification systems. It is especially valuable for evaluating pretreatment performance in reverse osmosis (RO) and nanofiltration applications, helping determine the effectiveness of pretreatment processes such as coagulation, filtration and clarification.
The SDI test measures the rate at which a 0.45 µm filter clogs under a constant pressure of 30 psi. Lower SDI values indicate reduced membrane fouling potential. The decrease in flow rate therough the filter is converted into an SDI value between 1 and 100, with higher values signaling inadequate pretreatment or elevated suspended solids, which can result in more frequent membrane cleaning or replacement. An SDI test of less than 3 is generally acceptable for membrane operation without pre-treatment. An SDI of greater than 5 generally indicates the need for additional upstream filtration.
The SDI test is a simple procedure which estimates the amount of particulate contamination in feedwater for RO and nanofiltration. The test specifically measures the rate of colloid and particulate fouling, ensuring feed water is clean enough to avoid frequent, costly membrane cleanings or replacements.
The index is a way to measure material (colloids, particulates, etc.) that would "clog" water purification devices. The results are used for the proper choice and placement of water purification devices (to lower a high Silt Density Index (SDI) score, pretreatment must effectively remove the fine colloidal and suspended particles that a standard 0.45 µm test filter captures).
The Silt Density Index (SDI) test is a simple and low-cost test. The only additional items you need in order to perform this test are a stopwatch and a 500 mL graduated cylinder. These are available as Hach Product Numbers 2630200 and 108149 respectively.
