Reductive Decolorization of Azo Dye by Bacteria - Microbial Degradation of Synthetic Dyes in Wastewaters - page 108

Reductive Decolorization of Azo Dye
by Bacteria

Guangfei Liu, Jiti Zhou, Jing Wang, Xin Zhang, Bin Dong
and Ning Wang

1 Introduction

Archaeological studies have found the application of colorants in cliff and cave
paintings by prehistoric human ancestors. Inorganic pigments include soot, ochre,
manganese oxide and hematite, while organic colorants contain kermes from
Kermes vermilio, alizarin from madder and indigo from natural origins. Then in
1856 William Henry Perkin, an 18 year old English chemist, accidentally discov-
ered the world rst synthetic dye in his attempt to synthesize the antimalarial drug

quinine. The bluish substance with excellent dyeing properties was later known as
mauveine or aniline purple. Since then, more than ten thousand synthetic dyes were
developed and the use of synthetic dyestuffs has now far exceeded natural dyestuffs
by the end of 19th century (Robinson et al. 2001 ). It was suggested that more than
10 5 different commercial dyes and over 7

' s

10 5 metric tons of dyestuffs are pro-
duced every year worldwide (Supaka et al. 2004 ).
The textile industry is the largest consumer of synthetic dye and uses high
quantities of water. Hence, it generates the highest amount of dye wastewater (Ali
2010 ). It was estimated that around 2.8

×

10 5 tons of textile dyes were discharged in ×

textile industry ef uent annually around the world (Jin et al. 2007 ). Depending on

the class of dye, its loss in ef uents during application could vary from 2 % to as

high as 50 %, which led to severe contamination of surface and ground waters in
the vicinity of dyeing industries (O

Neill et al. 1999 ). The dye concentration in
textile wastewater generally ranges between 10 and 200 mg l − 1 . Many dyes are
visible in water at a concentration as low as 1 mg l − 1

'

(Pandey et al. 2007 ).