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Many industries, such as dyestuffs, textile, paper and plastics, use dyes in
order to color their products and also consume substantial volumes of water. As a
result, they generate a considerable amount of colored wastewater. It is recognized
that public perception of water quality is greatly influenced by the color.
Color is the first contaminant to be recognized in wastewater (Banat et al., 1996). The presence of very small amounts of
dyes, such as methylene blue, malachite green, crystal violet, methyl
orange, etc., in water (less than 1 ppm for some dyes) is highly visible and undesirable (Robinson et al., 2001). Many of these dyes are also toxic and even carcinogenic and this poses a serious
hazard to aquatic living organisms (O'Neill et
al., 1999). The major effect of dyes on humans
is that they cause severe mutagenic and carcinogenic effects. Due
to increasingly stringent restrictions on the organic content of industrial
effluents, it is necessary to eliminate dyes from wastewater before it is discharged
(Wang et al., 2008).
In the past three decades, several physical, chemical and
biological decolorization methods were reported. A
few methods have been accepted by the paper and textile industries (Ghoreishi and Haghighi, 2003). Amongst
the numerous techniques of dye removal, adsorption is the procedure of choice
and gives the best results, as it can be used to remove different types of
coloring materials (Jain et al., 2003). In the present
investigation, untreated Psidium guajava L.f.
leaf powder was examined in an attempt to remove Congo red from
its aqueous solution.
Congo red is the sodium salt of
benzidinediazo-bis-1-naphtylamine-4-sulfonic acid. It is a secondary diazo dye. Congo red is water soluble, yielding a red
colloidal solution; its solubility is better in organic solvents such as
ethanol. |
