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12.10 CHAPTER TWELVE

costs and a lower waste discharge for higher equipment costs; these will be discussed
later.

Ammonia

Ammonia is a colorless gas that dissolves readily in water. It is commonly present in most
water supplies in trace quantities as the ammonium ion due to degradation of nitrogenous
organic matter. It may also be present due to the discharge of industrial wastes. Ammo-
nia reacts with water to form ammonium hydroxide, which dissociates into ammonium
(NH4 +) cations according to the following reaction:
NH3 + H20 ~ NH4 + + OH-
NH4 + (OH) ~ NH4 + + OH-
When ammonia is present in concentrations of a few parts per million, the degree of ion-
ization of ammonia is a function of the pH. At a pH below 8, ammonia is present pri-
marily as the cationic ammonium ion. At a pH above 9.0, ammonia is essentially un-
ionized and is not efficiently removed by salt cycle ion exchange.
Strong acid cation exchange resins, such as the kind typically used for softeners, will
exchange sodium for ammonium ions. The process is in fact a standard softener. The
cation resin has a higher affinity for divalent hardness ions; therefore hardness ions dis-
place the ammonia, which in turn displaces more sodium. As the service cycle continues,
the hardness ions form a band in the upper portion of the resin, and ammonia forms its
own band just beneath the hardness. Since ammonia removal is required, ammonia is in-
cluded as an exchangeable ion along with the hardness ions in sizing the system. The ser-
vice cycle is ended when ammonia levels in the softened water rise. If the service cycle
is allowed to continue past the ammonia break, the hardness will continue to load on the
resin and displace ammonia. Ammonia levels could reach concentrations in the effluent
equal to the total hardness plus ammonia concentrations in the raw water. This could be
much higher than influent ammonia levels. When this occurs, it is known as dumping.
Ammonia can also be removed by inorganic zeolites such as chabasite, mordenite, and
clinoptilolite. Some zeolites are more highly selective for ammonia than hardness and are
able to remove it throughout the acceptable pH range for potable water (6 to 9) without
the danger of dumping. Not having to remove hardness gives them very high throughput
capacities compared to strong acid cation resins for ammonia removal from waters con-
taining appreciable levels of hardness.

Barium

Barium is an alkaline earth metal which is occasionally found in groundwater primarily
in Arizona, Texas, Michigan, Vermont, and Florida. Barium is also present in trace
amounts in some surface waters with the highest levels occurring in the lower Mississippi
basin. Barium is very toxic when ingested as a soluble salt--a dose of even 550 mg is
considered lethal.
Barium Removal by Softeners. Barium is readily exchanged on to the strong acid cation
exchange resins in softeners. Barium has a higher selectivity for cation resins than either
calcium or magnesium (hardness), and is removed throughout the entire softening cycle.
It does not begin to leak until after hardness. The increase in barium caused by hardness
breakthrough, though small compared to the hardness leakage, may be sufficient to war-