Formula
SDIT = (1 − t0 ÷ tT) × 100 ÷ T, where T is the test interval in minutes. Percent plugging = (1 − t0 ÷ tT) × 100. If plugging is above 75%, the result is not valid; repeat the test with a shorter interval.
Test at 30 psi (2.07 bar) through a 47 mm, 0.45 µm membrane disc. The full method is in our SDI test procedure.
Related: RO plant calculator, ultrafiltration before RO, RO membrane cleaning.
FAQs
What SDI is acceptable for RO?
Below 3 is good; up to 5 is acceptable to most membrane makers. Above 5, improve pre-treatment.
What if the filter plugs in less than 15 minutes?
Run the test with a 5 or 10 minute interval and use that interval in the formula.