Environmental Engineering Reference
In-Depth Information
methods are often very costly and not environmentally safe. Furthermore, the
large amount of sludge generated and the low efficiency of treatment with respect
to some dyes have limited their use.
Keywords:
Natural dyes, acid dyes, disperse dyes, cationic dyes, adsorption,
membrane filtration, ion exchange, irradiation, electrokinetic coagulation,
aerobic and anaerobic degradation
1.1 Introduction
Water, which is one of the abundant compounds found in nature, covers
approximately three-fourths of the surface of the earth. Over 97% of the
total quantity of water is in the oceans and other saline bodies of water
and is not readily available for our use. Over 2% is tied up in polar ice
caps and glaciers and in atmosphere and as soil moisture. As an essential
element for domestic, industrial and agricultural activities, only 0.62% of
water found in fresh water lakes, rivers and groundwater supplies, which is
irregularly and non-uniformly distributed over the vast area of the globe,
is accessible [1].
A reevaluation of the issue of environmental pollution made at the
end of the last century has shown that wastes such as medicines, disin-
fectants, contrast media, laundry detergents, surfactants, pesticides, dyes,
paints, preservatives, food additives, and personal care products which
have been released by chemical and pharmaceutical industries, are a severe
threat to the environment and human health on a global scale [2]. The
progressive accumulation of more and more organic compounds in natu-
ral waters is mostly a result of the development of chemical technologies
towards organic synthesis and processing. The population explosion and
expansion of urban areas have had an increased adverse impact on water
resources, particularly in regions in which natural resources are still lim-
ited. Currently, water use or reuse is a major concern which needs a solu-
tion. Population growth leads to a significant increase in default volumes of
wastewater, which makes it an urgent imperative to develop effective and
low-cost technologies for wastewater treatment [3].
Especially in the textile industry, effluents contain large amounts of dye
chemicals which may cause severe water pollution. Also, organic dyes are
commonly used in a wide range of industrial applications. Therefore, it is
very important to reduce the dye concentration of wastewater before dis-
charging it into the environment. Discharging large amounts of dyes into
water resources, organics, bleaches, and salts, can affect the physical and
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