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12.22 CHAPTER TWELVE

It is important to remember that an ion exchange column can only remove ions and
that with wastewater contaminants, such as lead, the real story is that these types of con-
taminants are frequently not in an ionic form. Therefore, ion exchange alone may not be
suitable for their removal.

Fluoride

Bone char and activated alumina are both effective for fuoride removal and are the pre-
ferred exchange media. They are highly selective for fluorides over the other ions in wa-
ter. Strongly basic anion exchange resins are not used, because the fluoride ion is weakly
held and therefore not well removed. Activated alumina is a semicrystalline inorganic ad-
sorbent. Bone char is made from charred and steam-activated animal bones. It consists
basically of calcium hydroxy appetite, which bonds strongly to fluoride. Bone char is not
as readily available or as widely used as activated alumina, but both have been success-
fully used to reduce fluoride levels.
Defluoridation with activated alumina is similar to other ion exchange processes. The
alumina is generally in a column configured for downflow exhaustion and regeneration.
Because of limited kinetics, it's best to use bed heights of at least 3 ft. The pH of the wa-
ter being treated should be adjusted to 5.5 to 6.0. Unlike for organic-based ion exchang-
ers, the breakthrough curve is very gradual. Fluoride leaks from the column throughout
the service cycle. The endpoint of the service cycle is the maximum fluoride concentra-
tion to which the cycle can run that is acceptable to the user. Because of the ever-
changing breakthrough pattern, it is very difficult to blend as a technique to reduce treat-
ment costs. A more practical approach is to store the entire exhaustion cycle volume and
to run the system until the average over the entire cycle meets or is just below the max-
imum acceptable level.

Perchlorate
Perchlorate consists of an atom of chlorine surrounded by four atoms of oxygen. It oc-
curs as ammonium, potassium, magnesium, or sodium salts. These salts bind weakly to
soil particles and are not significantly broken down in the environment. Perchlorate salts
are extremely soluble and highly mobile and migrate faster and farther than other water
contaminants. These properties make perchlorate particularly persistent and problematic.
The primary source of perchlorate in the western United States is due to ammonium per-
chlorate, an oxidizing agent used in solid propellants. Its source is primarily from the pre-
viously legal discharges of wastewater from military installations and defense contractors.
Perchlorates are also used in a variety of manufacturing processes, such as car airbags,
leather tanning, fireworks, and electronic tubes. Prior to the 1960s, perchlorate was also
used as a medical treatment for patients with hyperthyroidism. Today, over 90% of the
perchlorate produced goes into solid rocket fuel.
Perchlorate impairs the thyroid function, because it is taken up in preference over io-
dide. As far back as 1966, perchlorate was identified as a suspected carcinogen. Although
the initial focus was on California, because of concentration of defense-related activities,
it became clear that other locations with defense activities were beginning to show up as
sources of significantly higher levels of perchlorate. In 1992 and again in 1995, the
USEPA-recommended concentrations for perchlorate in potable water were 1 to 5 ppb
(micrograms per liter) for children and 4 to 18 ppb for adults. The USEPA draft recom-
mendation in 2002 was lowered to 0.3 ppb for children and 1 ppb for adults. Later in