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12.54 CHAPTER TWELVE

suppliers and resin suppliers to determine the size and shape of the plant necessary to
meet a certain objective. The finished design is generally put out to bid, and the consul-
tant and end user will select an equipment supplier.
The equipment supplier builds the equipment, the installation contractor installs the
equipment, the end user and the equipment supplier commission the plant, and the end user
then takes over the operation of the finished exchange plant. The traditional roles played
by the various companies involved can lead to certain types of difficulties if the various
parties do not communicate well. The bidding process, particularly if the selection is made
solely on the basis of the lowest price, may lead to shoddy workmanship and subquality
components. Some types of partnering arrangements have been proved to provide a better
finished product at an overall price that is little or no more expensive than the total cost
provided by the traditional bid method of supply. Regardless of how the various roles are
played, it is extremely important that the end user take an active interest in the design and
construction of the ion exchange plant. The user who believes that by hiring a consultant
his or her work is finished, is very likely going to be unpleasantly surprised to receive the
finished product, as it will not likely be what the user had hoped to get.

FUTURE TRENDS IN ION EXCHANGE

It has become common to see ion exchange used in conjunction with membrane technol-
ogy, especially in applications with high salinity. In the future the role of ion exchange
will shift from bulk removal of ions toward selective ion removal and polishing. The use
of cation resins for water softening will continue as the largest single role of resins, even
as pretreatment for membrane processes. In some applications, the role of ion exchange
for bulk ion removal will diminish as membrane processes become more efficient. Ion
exchange polishing of membrane-treated waters will continue to grow. Ion exchange will
become more widely used for selective ion removal and product recovery, and purifica-
tion. Currently the areas of rapid growth in ion exchange are selective removal of con-
taminants such as nitrates, heavy metals, radioactive ions, and organic acids from potable
water supplies and for specific metal removal from wastewater streams.
There will be increasing reliance on the companies that provide exchange tank ser-
vices. Exchange tank services are ideally suited for point-of-use applications, especially
in polishing membrane effluents. They allow the regeneration of the ion exchange mate-
rial in bulk at centralized facilities. This includes the treatment of the regenerant waste-
water. Another recent trend is for owners to contract out the operation and maintenance
of the plants. This eliminates workforce, training, and management costs.

BIBLIOGRAPHY

Arsenic (See Also Selenium)
I. Arsenic (111) Oxidation and Removal from Drinking Water, Phyllis Frank and Dennis Clifford,
EPA, Project Summary, April 1986.
2. Arsenic, Arsenite (As02-1), Arsenate (As02-3), Organic Arsenic Complexes, Recognized
Treatment Techniques for Meeting the Primary Drinking Water Regulations for the Reduction
of Arsenic (As02 -1, As04 -3 and Organic Arsenic Complexes) Using Point-of-Entry (POU/
POE) Devices and Systems, Technical Application Bulletin, Water Quality Association, Feb-
ruary 1992.