Bacterial Degradation of Azo Dye Containing Wastes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 55

Bacterial Degradation of Azo Dye
Containing Wastes

Shailesh R. Dave, Tallika L. Patel and Devayani R. Tipre

1 Introduction

Till the late nineteenth century, all the dyes used were more or less natural with
main sources like plants, insects and molluscs, and were mostly prepared on a small
scale. It was only after 1856 that with Perkin

rst
synthetic dye, mauveine was manufactured on a large scale. At present there are
more than 100,000 commercial dyes available with a estimated production of
7

' s historic discovery of the

10 6 tons per year (Robinson et al. 2001 ). These dyes are used
extensively in the paper, clothing, food, cosmetic and pharmaceutical industries.
Because of the diversity of the dye components available for synthesis, a large
number of structurally different synthetic dyes are today utilized for coloration.
Among synthetic dyes, azo dyes are the largest and versatile class of dyes which
account for more than 50 % of the dyes produced annually. Azo dyes are aromatic
hydrocarbons and derivatives of benzene, toluene, naphthalene, phenol and aniline
(Puvaneswari et al. 2006 ). A wide variety of azo dyes with polycyclic, anthraqui-
none and triphenylmethane groups are being increasingly used in textile and
printing processes. Azo dyes contain one, two, three or more azo (

10 5 × 1 ×

-

) bonds
and based on this, they are grouped into monoazo, diazo, trisazo and polyazo dyes.
Some dyes are listed in Table 1 with their structure and molecular weight. The azo
group is substituted with benzene or naphthalene groups, containing many different
substituents, such as chloro (

N=N

- -

- Cl), methyl ( - CH 3 ), nitro ( - NO 2 ), amino ( - NH 2 ),

hydroxyl ( COOH) and thus forms different types of azo dyes

(Saratale et al. 2011 ). Azo dyes are highly stable and resistant to microbial attack.
Due to complexity of structure and electron withdrawing capacity of azo dyes, they
are considered xenobiotic compounds recalcitrant to biodegradation.

- OH) and carboxyl ( -