21857, Issue 24 Water Softener Elution ST

Regenerant drain line going to the
Water Softener sewer.

Elution Studies Procedure
By James McDonald, PE, CWT, 1. Measure the concentration of the brine
Technical Support Manager in the brine tank using the Salometer.
The brine tank should be 90% to 100%
Ion exchange is a physical process involving
saturated (90 to 100 Salometer
velocity, concentration, and time. Regeneration
degrees) at room temperature.
is a combination of the same three ingredients,
2. When the softener is ready for a
and if one or two of the variables are askew,
regeneration and has completed its
proper regeneration will not occur. Then each
backwash in the normal manner, make
subsequent regeneration will result in steadily
note of the time the brine cycle started.
reduced throughput.
3. Take a sample from the drain line as
During softener regeneration, calcium and soon as the softener switches to the
magnesium ions are “eluted” from the resin brine cycle.
beads with a highly concentrated salt (NaCl) Note: Be sure the sample is taken at a
solution. This is one of the most critical steps in point before water from a given softener
the entire ion exchange process and one of the unit has mixed with any other water
first places for problems to pop up. Monitoring source.
the parameters surrounding this “elution” step, 4. Transfer the sample to the 250-mL
or performing an “elution study,” is a very graduated cylinder, insert the
effective and easy investigative tool for the water Salometer, and take a reading.
treatment engineer. 5. Take samples every 2 to 3 minutes until
Tools the Salometer reading has dropped
below 5 Salometer degrees.
Tools required to perform an elution study 6. Make note of the time the brine cycle
include: was complete.
Salometer: A specialized hydrometer 7. Make note of the time when the softener
that measures the percent saturation of switches from slow rinse to fast rinse.
a brine solution (0-100%). 8. Plot the Salometer readings on graph
250-mL Graduated Cylinder: This is paper with time (minutes) on the X
used as a hydrometer jar for taking the horizontal axis and Salometer readings
Salometer readings. on the Y vertical axis.
Timer: Stopwatch, wristwatch, etc. 9. Connect the data points to make a
Graph Paper: To record Salometer curve.
readings versus time. 10. Draw a horizontal line at 30 Salometer
degrees.
Sampling Points
There are two sampling points for an elution
study:
Brine tank
Issue 24 – Page 1
Interpreting the Results second elution study can confirm that the
efficiency of operation has been improved.
Ideally, there should be 25-30 minutes where
the curve is above the 30 Salometer degree Figure 1: Interpretations of Elution
reading. This is known as the “30-30 Rule” Curves
where a solution of 30 Salometer degrees is in
contact with the resin for 30 minutes.
There are a number of operational factors that

may affect the appearance of the elution curve.
Figure 1 illustrates various possibilities and
states possible causes for the shape of each
curve. Factors that can adversely affect the
elution curve include:
Not enough brine drawdown.

Channeling of the resin bed.
Restricted brine line or eductor resulting
in a slow brine draw.
Restricted distribution system.
Improper adjustment of brine rinse
flowrate.
Unsaturated brine in brine tank.
Brine Usage
The brine usage can be calculated by measuring
the diameter of the brine tank and the depth of
the brine before and after the brine draw. You
will need the following information:
2
h
h = height of brine used.

Assume a void space of 40% between
the solid salt pellets.
At 100% saturation, 1 gallon of brine
contains 2.647 pounds of salt.
Conclusions
References:
How to Survey a Sodium Zeolite Water
An unconventional elution curve may not be able Softener, Allan Basset, Analyst, Winter 2001.
to pinpoint the cause of a problem, but it can
Procedures of Industrial Water Treatment, J.
confirm that a problem exists. After a review of
N. Tanis, Ltan, Inc., 1987.
the operating procedure and perhaps an
evaluation of a sample of resin has been Ion Exchange Manual, CROWN Solutions,
Inc., 1997.
completed, corrective action can be taken, and a
Crown Solutions Co., LLC

Issue 24 – Page 2 945 South Brown School Road
Vandalia, OH 45377
(937) 890-4075
www.crownsolutions.com

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21857, Issue 24 Water Softener Elution ST

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Regenerant drain line going to the

Water Softener sewer.

There are a number of operational factors that

Not enough brine drawdown.

h = height of brine used.

Crown Solutions Co., LLC

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