Long term, successful operation of any water softening system depends upon the care and attention it
receives. Ordinarily, water treatment systems will provide uniform performance after the initial start-up
period and operation is stable. Gallonage delivery between regenerations and treated water purity
usually do not vary appreciably over the life of the resins--as long as the mineral content of the
incoming water does not change.
This manual is intended to be a practical reference guide for all operating personnel. In view of the
fact that system performance can change very dramatically throughout the year, a discussion of "ion
exchange" theory is included in addition to basic information relative to equipment operation and
regeneration procedures. Thorough understanding of the simple chemical reactions will help to
determine if some equipment malfunction has occurred, or if the system is simply responding to
changing water conditions. For this reason, all operation and supervising personnel are encouraged
to study Section 2, which define terminology and the simple chemistry associated with this system.
Ion exchange (i.e., the softening process) is a reversible reaction. Ion exchange softening resins have
only a limited capacity for removing calcium and magnesium minerals. If the volume of water put
through a resin bed exceeds its capacity, some hardness will start sloughing off into the treated water.
Therefore, service runs must be terminated before this breakthrough occurs. When a run is over, the
resins are treated with sodium chloride salt to displace the hardness and restore its removal capacity
again. This process is termed "regeneration".
The degree of softening that can be accomplished depends upon several factors. The primary
influences are the incoming water composition, type of resins used and amount of salt used.
Secondary influences are the concentrations and flow-rates at which NaCl is applied.
2. PRINCIPLES OF ION EXCHANGE IN THE SOFTENING PROCESS
2.1 ION EXCHANGE SOFTENING PROCESS
In order to understand what happens in the ion exchange softening process, it will first be
necessary to understand the meaning of the terms that are used in the explanation. HARD
WATER, CATION EXCHANGER, and BRINE are therefore defined below and then used to
show how the ion exchange process works.
A. Hard Water - All natural waters contain much the same dissolved impurities, but in
widely varying amounts. There are always enough ANIONS (-) present to balance the
CATIONS (+), but anions have no effect on the ion exchange softening process.
Water will be HARD, i
f it contains large amounts of Calcium (Ca++) and/or
Magnesium (Mg++) ions.
B. Brine - water in which SALT has dissolved. SATURATED brine contains as much salt
as it is possible to hold in solution (approx. 26% to 27%).
SALT - SODIUM CHLORIDE (NaCl). When dissolved in water it splits up (ionizes)
into Sodium (Na+) ions and Chloride (Cl-).
SATURATED BRINE - contains a very great number of Na+ and Cl- ions
(concentration is over 200,000 ppm). When used to regenerate a CATION
EXCHANGER, only the Sodium ions (Na+) are put to use. The Chloride ions (Cl-) do
not work in the process.
C. Cation Exchanger - a solid material that has a very large number of "REACTION
POINTS". These reaction points have NEGATIVE (-) electric charges, and are able to
attract and hold CATIONS, which are POSITIVELY (+) charged (much the same way
as the way opposite poles of a magnet attract each other).
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