Silt Density Index Testing
SDI is used mainly for RO or nanofiltration systems. It is a measurement of fouling potential. It measures the time required to filter a fixed volume of water through a standard 0.45µm pore size microfiltration membrane with a constant given pressure of 30 psi (2.07 bar). The SDI gives the percent drop per minute in the flow rate of the water through the filter, averaged over a period of time such as 15 minutes.
This test is necessary because of the very tiny particles suspended in the water. As you know, a glass of drinking water from a municipal system may appear crystal clear to the eye but can easily contain tiny particles that will blind over the R/O membrane very quickly. The water treater needs to know how much is present and if they will need a pre-filter system.
