Silt Density Index (SDI) Membrane Fouling Calculator

Determine ASTM D4194 Silt Density Index ($SDI_{15}$) and plugging rate percentage ($P_{30}$) to verify reverse osmosis feed water pretreatment compliance.

ASTM D4194 Test Measurements

Initial 500 mL Collection Time t_i (sec): Time to collect 500 mL at start

Final 500 mL Collection Time t_f (sec): Time to collect 500 mL after test

Total Test Duration T (minutes):

Feed Test Pressure (psig): ASTM requires 30.0 ± 1.0 psig

SDI Index & Membrane Suitability

Silt Density Index (SDI):

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Filter Plugging Rate (%P_30):

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RO Warranty Acceptance:

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Pretreatment Requirement:

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ASTM D4194 Silt Density Index Standard

The Silt Density Index (SDI) is the universally accepted empirical benchmark used to quantify colloidal and particulate fouling potential of reverse osmosis feed water. A constant feed pressure of $30.0\text{ psig}$ ($2.07\text{ bar}$) is applied across a $47\text{ mm}$ diameter, $0.45\text{ µm}$ microporous cellulose membrane filter.

Manufacturer Warranty Thresholds

Leading membrane manufacturers (Dow FILMTEC, Hydranautics, Toray) specify strict warranty limits: $$\text{SDI}_{15} < 5.0 \quad (\text{Absolute maximum for spiral-wound elements})$$ $$\text{SDI}_{15} < 3.0 \quad (\text{Recommended for extended 3-5 year membrane lifespan})$$

Silt Density Index (SDI) Membrane Fouling Calculator

ASTM D4194 Test Measurements

SDI Index & Membrane Suitability

ASTM D4194 Silt Density Index Standard

Manufacturer Warranty Thresholds

Frequently Asked Questions