Biosorption of Organic Dyes: Research Opportunities and Challenges - Green Chemistry for Dyes Removal from Wastewater - page 296

GlcN: Glucosamine
GlcNAc: N-acetyl-glucosamine
pH zpc : point of zero charge
SEM: Scanning electron microscopy
SODs: Synthetic organic dyes
T: Temperature
8.1 General Considerations
8.1.1 Dye-Containing Effluents
Mankind has used dyes for thousands of years, and the first known use of
an organic colorant was nearly 4000 years ago, when the blue dye indigo
was found in the wrappings of mummies in Egyptian tombs. In 1856,
William Henry Perkin accidentally discovered the world's first commer-
cially successful synthetic dye. Starting that year, dyes were manufactured
synthetically and on a large scale [1]. Synthetic organic dyes (SODs) are
extensively used in many fields such as the textile industry, leather tanning
industry, paper production, food technology, agricultural research, light-
harvesting arrays, photoelectrochemical cells and in hair colorings [2]. The
SODs are indentified by their color index (C.I.) and classified as: acid dyes,
basic dyes, disperse dyes, direct dyes, reactive dyes, solvent dyes, sulfur
dyes and vat dyes [3]. Overall, at present there are more than 100,000 com-
mercial dyes with a rough estimated production of 7 10 5 -1 10 6 tons per
year [4]. A portion of these dyes is lost in the manufacturing and process-
ing units, and are destined for industrial effluents [5].
The dye-containing effluents (DCEFs) are characterized by high alkalin-
ity, biological oxidation demand, chemical oxidation demand, and total
dissolved solids with dye concentrations generally below 1 g L -1 [6]. he
inadequate disposal of untreated DCEFs in water bodies causes serious
direct and indirect impacts on the environment and human health. Some
direct impacts are: color change, poor sunlight penetration, damage on
flora and fauna, ground water pollution, depletion of dissolved oxygen and
suppression in the reoxygenation capacity. The indirect impacts are: killing
of aquatic life, eutrophication, genotoxicity, microtoxicity and damage to
the immune system of human beings [7]. Thus, several governments have
established environmental restrictions with regard to the quality of DCEFs
and this has obligated the industries to remove dyes from their effluents
before discharge [8]. However, DCEFs are very difficult to treat, since
the dyes are recalcitrant molecules with a complex aromatic structure,