Dye Adsorption on Expanding Three-Layer Clays - Green Chemistry for Dyes Removal from Wastewater - page 332

consumption of dyes has increased in other industries like cosmetics, pulp
and paper, paint, pharmaceutical, food, carpet, and printing industries. In
addition to coloring the wastewater, dyes and their breakdown products are
toxic, carcinogenic, and mutagenic to life forms, and they can cause allergies
and skin diseases [6-9]. Removal of dyes from wastewater is generally dif-
ficult. They are recalcitrant organic molecules that have complex aromatic
structures. They are usually biologically non-degradable; are resistant to
aerobic digestion; and are stable to light, heat and oxidizing agents [10,11].
The treatment and decolorization processes that have emerged during the
past three decades remain plagued by cost and disposal problems. Their
specific advantages and disadvantages are compared in Table 9.1 [5,12-15].
Adsorption is one of the best treatment methods due to its flexibility,
simplicity of design, and insensitivity to toxic pollutants. Activated carbon
is the most popular adsorbent, and has been cited by the US Environmental
Protection Agency as one of the best available control technologies [15].
However, because activated carbon production and regeneration is expen-
sive, considerable attention has been given to other low cost and easily
available adsorbents for dye removal. Recently, clay and its modified forms
have been used as adsorbents, and there has been an upsurge of interest in
the interactions between dyes and clay particles.
Clay may serve as an ideal adsorbent because of its low cost. It has rela-
tively large specific surface area, excellent physical and chemical stability,
and other advantageous structural and surface properties. For example,

Table 9.1 Principal, existing and emerging processes with their advantages and
disadvantages for removal of dyes [5,12].

Methods Advantages Disadvantages

Oxidation Rapid and efficient process (H 2 O 2 ) agent needs to

activate by some means;
high energy cost;
chemicals required;
sludge generation

Advanced oxida-
tion process

No sludge production; little
or no consumption of
chemicals; efficiency for
recalcitrant dyes

Economically unfeasible;
formation of byproducts;
technical constraints

Ozonation Ozone can be applied in its

gaseous state and does
not increase the volume
of wastewater and sludge

Short half-life (20 min)

( Continued )