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Test for determining Silt Density Index

Equipment
  • Millipore Filter Pad Holder with a 0.45 micron filter disc.
  • 500 ml. Graduated cylinder
  • Stopwatch
  • Dull Tweezers
Procedure
  • Unbolt the filter holder, wet it, and place a 0.45 micron filter on the back-up plate using the dull tweezers.
  • Place the "O"-ring properly and then replace the top half of the filter holder and bolt loosely.
  • Connect apparatus to the feedwater line (minimum 30  PSIG) in a vertical, downflow position and open the needle valve a crack.
  • Loosen two adjacent filter-holder bolts, tilt the apparatus and bleed out all trapped air, then retighten bolts and adjust the pressure to 30 PSI while starting the stopwatch.
  • Immediately run the flow into the graduated cylinder and measure the time required to collect 500 ml, maintaining a pressure of 30 PSIG during the run.  Mark the time (t1) and keep the watch running.
  • Repeat the previous step immediately after 5, 10, and/or 15 minutes of total elapsed time.  Mark the collection times (t5, t10, tF).
  • Close the sample valve and disconnect he apparatus after the 15 minute reading.  Remove the disk and place it in a plastic bag for later examination.
Calculation
  • Calculate the ratios R = t1/t5 , t1/t10 and/or t1/tF.
  • Estimate % P30 at the selected time(s) from the following equation:
    % P30 = [1-R] 100.
  • Estimate the Silt Density Index, SDI, from the following equation:
  • SDI = % P30 Elapsed Time (minutes)

The 15-minute index will generally be the lowest of the three, and should be used for filter sizing purposes.

 

 

 
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All Content on this site is  intended for informational purposes for experienced water treatment professionals only.  Applied Membranes, Inc. does not assume any liability for any damages caused by the misapplication or misinterpretation of any of the information contained on this website.
Applied Membranes, Inc. 2007