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ION EXCHANGE APPLICATIONS IN WATER TREATMENT 12.27

Operating Cycle. During the service cycle, all the anions are loaded on the resin and
exchanged for an equal amount of chlorides. During the early portion of the service
cycle, the effluent will contain only chloride ions. As the service cycle continues, se-
lenates continue to load onto the inlet portion of the resin and displace the previously
loaded sulfates down the column. The sulfates do likewise to the nitrates and chlo-
rides, which in turn displace the bicarbonates, which have the lowest relative affinity.
The bicarbonates appear first in the effluent, followed by chlorides and nitrates and
then the sulfates. At these low concentrations, the divalent ions are much more strongly
held. The presence of high levels of chlorides or bicarbonates in the inlet water will
have only a negligible impact on the capacity of the resin for selenium. Selenium leak-
age will remain low throughout the service cycle until sulfate breaks through. The sul-
fates will displace a portion of the selenium from the bottom of the bed, left over
from the previous regeneration, and selenium levels will rise soon after the sulfate
levels increase.

Radioactive Substances (Terrorist-Related)
Ion exchange solutions to terrorist acts will likely be looked at primarily for removal of
radioactive substances. Although some poisons, such as cyanide, can be removed by ion
exchange, they are usually better dealt with by already in-place treatment methods such
as pH adjustment and chlorination. Radioactive substances could come in small quanti-
ties from using "dirty bombs" (conventional explosives with radioactive substances at-
tached) as the delivery/dispersant system. The short-term radioactive dose and exposure
may be very small, even within acceptable limits at the municipal level. Longer-term so-
lutions will probably involve ion exchange. It's believed that radioactive hydrogen, ce-
sium, and iodine might be involved, because they are commercially available for indus-
trial/medical uses. Other possible candidates are those present in waste streams and spent
fuel rods of nuclear generating systems, such as tritium; cobalt; cesium; strontium; plu-
tonium; radioactive isotopes of iron, zinc sodium, manganese, and zinc plus others; and
strontium, rubidium, and iodine.
Ion exchange can easily remove these substances. The same strongly basic resins that
are used for nitrate and perchlorate removal are also highly selective and useful for io-
dine and uranium removal. The biggest problem is the disposal of the resins or the treat-
ment of the waste regenerant that could be 100,000 times more concentrated than the un-
treated influent. Specific regeneration schemes, based on existing technology and resin
selections will vary depending on the ionic composition of the water. Likewise, so will
the process scheme and resin selection. Single use/replacement/disposal versus regenera-
tion with or without postprocessing and reclaim are just some of the scenarios to be con-
sidered. Most of, if not all, these can be accomplished with existing technology, but lead
times for delivery are typically measured in months and, in the aftermath of a terror in-
cident, could become years. Preplanning using current treatment processes and water sup-
plies should be looked on as insurance. Information on removal of several radioactive
substances is listed below.

Radioactive Cobalt. Cobalt is not soluble in potable water. If cobalt is present, it will
be in solid form and best removed by filtration.

Radioactive Cesium. This can be removed with the same resins used for ammonia. In
the case of waters containing ammonia or where chloramination is practiced, the water
should be treated prior to adding ammonia because ammonia is a major competitor (as
also potassium) for the cesium selective resins (see ammonia).