Environmental Engineering Reference
In-Depth Information
[1, 2, 3, 4, 5, 6]. h e United States Environmental Protection Agency
(USEPA) has classii ed heavy metals as priority pollutants. Heavy metal
pollution in aqueous solutions has become a serious threat today and are
of great environmental concern as they are non-biodegradable, and thus
persistent in nature. Lead (Pb), cadmium (Cd), chromium (Cr), nickel
(Ni), cobalt (Co), zinc (Zn) and copper (Cu) are such metals, which are
frequently present in polluted water from various industrial processes such
as catalysts, mineral processing, electrical apparatus, painting and coat-
ing and agricultural materials [7, 8, 9]. Additionally, heavy metals are not
biodegradable and tend to accumulate in living organisms, and can cause
severe problems to both human health and wildlife. Natural processes and
human activities have polluted and reduced the quality of water resources
all over the world. Groundwater and superi cial water have been contami-
nated in various ways; e.g., by mining wastes, by agricultural chemicals, by
industrial and domestic sewage that is sometimes discharged without treat-
ment into waterways and by natural trace elements (e.g., arsenic). Since it
is important to eliminate or reduce the concentration of heavy metals in
the aquatic ecosystems, various methods and technologies are commonly
applied in the treatment of mining and rei ning industrial el uents before
they are discharged to receiving water. h ese methods include precipita-
tion, ion exchange, and membrane processes. However, the application of
some of these methods may be impractical due to economic constraints or
may be insui cient to meet strict regulatory requirements. Furthermore,
they may generate hazardous products or products which are dii cult to
treat [10, 11]. h e traditional coagulation and l occulation processes use
inorganic coagulants such as aluminium hydroxides in drinking water
treatment. Metal coagulants can be used to partially remove heavy metal
from wastewater [12], but, the use of metal coagulants is not 100% ef ective
for removing metal cations from water at pH 7. h e high cost of adsorbents
such as activated carbon and some ion-exchange resins used for the treat-
ment of water and wastewater have led to new, more ef ective and cheaper
adsorbents. Bailey
et al.
[13] have mentioned that natural materials that are
available in large quantities or industrial waste products can also be used
as adsorbents.
11.2
Sources of Heavy Metals in the Environment
Various industries that generate wastewater containing heavy metals
include the tanning, battery, glassware, ceramics, electroplating, fertilizer,
mining, paints, and photographic industries. h ese wastewaters contain
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