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ION EXCHANGE APPLICATIONS IN WATER TREATMENT 12.53

self. In the case of cation resins, the two most likely leachables are benzene sulfonic acid
and sulfa benzylic acid. In the case of anion resins, the most likely leachables are the
functional groups and are generally classified as amines. The dominant leachable from
type I strong base resins is trimethylamine, and the dominant leachable from type II an-
ion resins is acetaldehyde. In cases of severe oxidation, the anion resin can also have
leachables that are made up of portions of the polymer.
Leachable levels are always highest when the resin is new or when it has been allowed
to stand for a period of time; this decreases with age. The concentration drops when the
flow increases. This is so because the resin is deteriorating at a relatively constant rate and
the leachables diffuse into and are diluted by the surrounding water. This is one reason why
an ion exchange bed that has sat idle for more than full cycle time should be rerinsed be-
fore its return to service. Under normal steady-state operation, and in the absence of foul-
ing, the leachable concentrations will decline to the low parts per billion range. To avoid
the unnecessary deterioration of an ion exchange resin bed, the bed should be protected
from strong oxidants such as chlorine, chloramine, ozone, hydrogen peroxide, potassium
permanganate, or even oxygen if the feedwater temperature is above 140 ° F.

Guidelines for Resin Replacement
Generally speaking, if no specific guidelines exist, ion exchange resins should be replaced
when their useful capacity has deteriorated by 25% from the performance when the resin
was new or if the total volume of resin has decreased by 25% or more and the resin is
not in "like new" condition. This is the point in many cases where economics favor the
replacement of the resin and the cost of the resin is offset by savings in regenerant and
waste treatment costs. Somewhere around 25% to 50% loss of total capacity usually re-
suits in a deterioration of water quality in addition to the reduction in throughput. Other
criteria for resin replacement include failure to make sufficient quantities of good-
quality water, failure to rinse up to service quality in a reasonable time.
It is generally better not to top off ion exchange beds simply because a small per-
centage of the total resin volume has been lost, particularly if the capacity of the resin is
significantly degraded. It is generally more efficient to operate with reduced throughput
until such time as the entire bed can be replaced. This is not always practical as the loss
of throughput capacity may necessitate increased numbers of regenerations, which may
overtax the wastewater system or the operator's ability to maintain continuous service.

BOUNDARIES BETWEEN SUPPLIERS, CONSULTANTS,
AND USERS

The process of creating an ion exchange system usually involves a resin supplier, an equip-
ment supplier, a consultant or design engineering firm, a contractor (both mechanical and
electrical), and an end user or operator of the finished plant. Except for relatively small
systems, it is unlikely that the role of these various suppliers and users will be handled
by a single company. These roles will almost always be handled by various companies
who must all work together and cooperate to have a successful ion exchange plant. The
end user must begin the process of creating the plant by collecting information about
needed water quality and quantity. The end user must determine that the plant will be
built, must economically justify it, and must secure capital for its construction. The end
user will then generally contract with a design engineering consultant to create a specifi-
cation for the finished ion exchange plant. The consultant will then work with equipment