Environmental Engineering Reference
In-Depth Information
Cobalt has both benei cial and harmful ef ects on human health. Cobalt
is benei cial for humans because it is part of vitamin B
12
, which is essential to
maintain human health. However, if too much cobalt gets into our body, harm-
ful health ef ects can occur. Serious ef ects on the lungs, including asthma,
pneumonia, and wheezing have been found in people exposed to 0.005 mg
cobalt/m
3
. Absorption of nickel following oral exposure has been shown to
vary (3-40%) depending on whether the nickel was in drinking water or food,
with greater absorption occurring with drinking water. About 20-35% of the
inhaled nickel that is retained in the lungs is absorbed into the blood. Most of
the absorbed nickel is excreted in the urine, regardless of the route of expo-
sure. Adverse respiratory ef ects have been reported in humans and animals
exposed to nickel compounds at concentrations much higher than typically
found in the environment. In nickel workers, exposure to nickel did not result
in increases in the risk of death from nonmalignant respiratory system dis-
ease. h e cellular bioavailability of nickel (Ni), ie, the ability of nickel to enter
target cells and to release nickel ions, appears to be a major determinant of the
carcinogenic and toxic ef ects of nickel compounds [50, 51, 52, 53].
Due to their detrimental ef ects on human beings and biodiversity, it
has become necessary to remediate the wastewater containing heavy met-
als and industrial el uents. Various methods exist for the removal of heavy
metal ions from wastewater which include chemical precipitation, coagu-
lation, membrane technology, electrolytic reduction, ion exchange, and
adsorption. Ion exchange is the most widely used method for heavy metal
removal from aqueous streams. During removal, recovery, or processing
of metals, ion exchange acts as a concentrator of metals. Coagulation-
l occulation can also be employed to treat wastewater ladened with heavy
metals, wherein the coagulation process destabilizes colloidal particles by
adding a chemical agent and results in sedimentation. Membrane i ltration
has received considerable attention for the treatment of inorganic el uent,
since it is capable of removing not only suspended solid and organic com-
pounds, but also inorganic contaminants such as heavy metals. Amongst
all the treatment processes mentioned, adsorption using sorbents is one
of the most popular and ef ective processes for the removal of heavy met-
als from wastewater. h e adsorption process of ers l exibility in design
and operation and in many cases produces treated el uent suitable for
reuse, free of color and odor. In addition, because adsorption is sometimes
reversible, the regeneration of the adsorbent with resultant economy of
operation may be possible. Activated carbon adsorbents are used widely in
the removal of organic contaminants and, to a lesser extent, in the removal
of heavy metal contaminants in product purii cation and pollution control.
In spite of its prolii c use, activated carbon remains an expensive material
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