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ION EXCHANGE APPLICATIONS IN WATER TREATMENT 12.49

these types of personnel are generally more familiar with the chemistry involved in the
process.
Maintenance. General maintenance of an ion exchange system includes cleaning the
equipment periodically, particularly in the area of the dilution stations, as the regenerant
chemicals are corrosive. If the equipment area is not kept clean, rapid deterioration of the
hardware will occur. Other routine maintenance requirements such as replacing valve di-
aphragms and repairing pump seals are generally the same as for other systems that em-
ploy this type of hardware. With respect to the ion exchange system, the maintenance re-
quirements tend to be less predictable and are performed at irregular, long intervals.
Although ion exchange plants are not designed with the intent that the resin will foul,
it is not uncommon for one or more contaminants in the feedwater to cause resin fouling
over time. One of the more significant maintenance requirements is cleaning the ion ex-
change resin. Resin cleaning may be nothing more than an occasional (yearly) extended
backwash under manual supervision to remove excessive suspended solids and broken
resin beads that have accumulated, to something as complicated as repeated chemical
cleanings with various acids, salts, and caustics. The specific cleaning process depends
on the nature of the contaminant or foulant. When the foulants are not able to be suffi-
ciently removed, it necessitates resin replacement. Many of the chemicals used to clean
resin are not compatible with the materials of construction of the equipment. Therefore,
it is not uncommon to have to clean the resin externally. Resin cleaning procedures gen-
erally involve a minimum of 8-h outage time and must be followed by extraordinary re-
generation before the resin bed can be put back into service. Some of the resin cleaning
chemicals are hazardous and must be properly stored, handled, and disposed of. For this
reason it is usually impractical for small systems to be cleaned, and it is most common
to see the resin replaced when it becomes fouled, rather than cleaned. Even in large treat-
ment systems, the economics involved may favor resin replacement over resin cleaning.
Today some of the exchange tank or water treatment service companies will perform resin
cleaning services for a fee. This avoids tying up operating vessels and allows time for
more vigorous treatments, which may eliminate the need to change out the resin beds.
Resin Removal and Replacement. Resin removal and replacement is a periodic main-
tenance requirement that occurs in all ion exchange systems sooner or later. If the system
operates in an unfouled manner, the interval between resin replacements may be in ex-
cess of 10 years for water softeners and cation exchangers and 3 to 6 years in anion ex-
changers. However, the average is 3 to 5 years, and in cases where the water fouls the
resin, it can be even more often. For small household systems or with small exchange
tanks that can be picked up, it is relatively simple to unscrew the top, pick the tank up,
turn it upside down, and shake the resin out, using a hose to sluice out any resin that
clings to the inside wall of the vessel. For larger systems, the resin can be sluiced or si-
phoned out of the vessel. In urban areas there are vacuum truck operators that, for a fee,
will remove the resin by vacuuming it out of the tank. It is important to clean out the tank
as well as possible before refilling with fresh resin, particularly if the resin is being re-
moved because of fouling. After the resin has been removed, while the tank is s011 empty,
the maintenance personnel should always take advantage of the opportunity to inspect the
tank and internals for signs of wear or damage. In small systems this can be accomplished
by peering into the tank with a flashlight. However, there is no substitute for closer ex-
amination by a maintenance worker actually climbing inside the tank. In the inspection
the worker should look for signs of bent or broken parts, excessive corrosion, gaskets that
may have slipped, etc. The internals are not indestructible, and the worker who enters the
vessel must be careful not to step on and thus damage the internals by his or her entrance.
If the tank is lined, the lining should be examined for signs of blistering, tears, corrosion