SDI Kits

For information on:
1) Manual SDI Kit
2) Auto SDI Kit

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 colloidal 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.

The Sterlitech Auto SDI 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 Sterlitech Auto SDI 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 by automatically maintaining a constant 30 psi (2.07 bar) in the feed stream to the filter.

Flow rates are measured during the collection of 500 mL samples at the start of the test and after 5, 10, and 15 minutes. SDI units (percent decay per minute) represent the degree of plugging that may occur due to the feedwater stream particulate and colloidal levels. The 15 minute SDI (SDI 15) is defined by ASTM D 4189-95 as the interval required for accurate and standardized testing. The 5 and 10 minute SDI values are only estimates of the 15 minute value.

In addition to calculating SDI 15, the measured decay in flow rate is also converted from an SDI value to plugging factor (PF) value, a number between 1 and 100%. 100 percent means the filter is completely plugged. This provides an understandable point of reference for the potential of your RO membranes to plug — the higher the percentage, the faster your membranes may become fouled with particulates.

Manual SDI Kit 

• Manual kit
• Small case holds membranes

Applications

• Silt density index for water and wastewater

The Sterlitech Manual SDI Kit is used to indicate the quantity of particulate contamination in relatively low-turbidity water supplies or waste streams.

Based on ASTM Method 4189-95, the test is accepted industry-wide to estimate the rate at which colloidal and particle fouling will occur in water purification systems.

The SDI test measures the decay in flow rate through a 47 mm diameter, 0.45 µm pore size membrane. The 0.45 µm membrane is chosen because it is more susceptible to plugging from colloidal matter than from hard particles such as sand or scale.

The decay in flow rate is converted to a number between 1 and 100. The lower the silting density index number, the lower the fouling tendencies of the water. To ensure economic and efficient operation, most manufacturers of reverse osmosis systems recommend a silting density index of 5 or less.

The Silting Density Index Test Kits include a pressure regulator with gauge, a 47 mm filter holder, membrane discs, and all necessary valving, tubing and fittings in a plastic case. Sterlitech's standard kit contains a box of cellulosic membrane filters that conform to all requirements of the ASTM method.With this kit, additional apparatus required is a graduated cylinder and stopwatch

Specifications

Additional equipment not provided:

• Graduated cylinder, 500 mL, polypropylene, graduations 5 mL, for SDI testing
• Stopwatch for SDI testing, 0.2 second increments
• Replacement cellulosic filters for SDI testing, MCE4547100, Nitrocellulose, Mixed Esters (MCE), 47 mm, 0.45 µm pore size, 100 per package

Auto SDI Kit

• In-Field flow calibration
• Built to ASTM 4189-95
• No special tools or skills required
• Push-button operation
• Turn it on and walk away
• Lightweight and portable
• Rugged carrying case
• Audible alert with silence mode
• Repeatability within 0.2 SDI units
• LCD display
• Results remain on screen until reset
• Continuous flow readout in mL/min
• Global voltage compatibility
• In-Field flow calibration
• Membrane replacement availabilty on-line

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 Auto SDI from Sterlitech.

Sterlitech Auto SDI 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 Sterlitech Auto SDI 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 Sterlitech Auto SDI kit or Silt Density Index Testing System, as shown above, includes the tester, carrying case, 12 VDC Power Supply, pressure guage, inline prefilter, SDI membrane filters (box of 100), and a user’s manual.

Replacement cellulosic filters for SDI testing, MCE4547100, Nitrocellulose, Mixed Esters (MCE), 47 mm, 0.45 µm pore size, 100 per package  

To view ASTM documentation for SDI testing, please refer to this document. 

The Fast, User-Friendly, and Accurate Way of Measuring Silt Density Index

1. Connect Water
2. Insert Filter
3. Press Button
4. Read Results

Product Characteristics

• Range, SDI (15 minutes): 0–6.7 SDI units
• Range, Plugging Factor: 1-100% plugged
• Electrical Power Selection: 110-120V 60Hz or 220-230V 50 Hz
• Water Supply: 1/4-inch OD tubing via quick-connect, 0.8 gpm (3.0 Lpm) flow
• Water Pressure - psi (bar): 65-100 (4.5-6.9)
• HxWxD - inches (mm): 6x14x10 (15x36x26)
• Weight - lb (kg): 8.0 (3.6)

For more information: click here to view the Auto SDI Manual