Fact Sheet

AutoSDI
Automated Silt Density Index Tester
SDI Testing Made Easy
If you thought performing a silt density index (SDI)
test to predict membrane fouling potential was too
tedious, costly and time consuming, welcome to
AutoSDI from GE’s Water & Process Technologies!
AutoSDI eliminates the need for stopwatches,
graduated cylinders, calculators and tedious labor.
In less than twenty minutes you will know 5, 10,
and 15-minute SDI results as well as
Plugging Factor.
Fouling membranes and compromising water quality can be expensive. With the simple AutoSDI kit
and a water source of 65 psi (4.5 bar) and at least
0.8 gpm (3.0 Lpm), membrane particulate fouling
can be avoided and system performance optimized.
The AutoSDI kit or Silt Density Index Testing System,
as shown in Figure 1, includes the tester, carrying
case, 12 VDC Power Supply, pressure guage, inline
prefilter, SDI membrane filters (box of 100), and a
user’s manual.

What is the Silt Density Index
Silt Density Index (SDI) testing quantifies the amount
of particulate contamination in a water source. SDI
is widely accepted for estimating the rate at which
collodial and particulate fouling will occur in water
purification systems–especially in applications using reverse osmosis (RO) membranes. Water
sources often change their water quality and this
test often needs to be done weekly or monthly.

Figure 1: AutoSDI

The AutoSDI Tester automatically calculates a relative value for the amount of suspended matter in
feedwater streams. Measured values reflect the
rate at which a 0.45-micron membrane filter will
plug with particulate material when feedwater is
flowing through it. The ASTM chose the 0.45 micron
filter because it is more likely to clog from colloidal
matter than from hard particles such as sand or
scale. SDI testing is commonly used as an “early
alert” to ensure that particulates in feedwater do
not plug the micropores in RO membranes.

How is SDI Calculated?
The AutoSDI calculates SDI based upon the decay in
flow rate during a 15-minute period across a new
0.45-micron filter installed in the built-in holding
fixture. Flow rate measurement accuracy is ensured
Find a contact near you by visiting www.ge.com/water and clicking on “Contact Us”.
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FS1061EN.doc Feb-11