Bacterial Enzymes and Multi-enzymatic Systems for Cleaning-up Dyes from the Environment - Microbial Degradation of Synthetic Dyes in Wastewaters - page 26

Bacterial Enzymes and Multi-enzymatic
Systems for Cleaning-up Dyes
from the Environment

S ó nia Mendes, Maria Paula Robalo and L í gia O. Martins

1 Introduction

Synthetic dyes are xenobiotic compounds that are being increasingly used in several
industries, with special emphasis in the paper, textile and leather industries. Over
100,000 commercial dyes exist today and more than 7 10 5

× tons of dyestuff is

10 5 tons is released into the wastewaters (Rai
et al. 2005 ). Among these, azo dyes, characterized by the presence of one or more
azo groups (

produced annually, of which 1 1.5 ×

-

), and anthraquinonic dyes represent the largest and most
versatile groups. Synthetic dyes are highly visible pollutants and can hardly be
removed from the ef

N=N

- -

uents by conventional wastewater treatments. They are
anthropogenic pollutants causing deterioration of water quality, affecting photo-
synthesis, decreasing dissolved oxygen levels and severely disturbing the aquatic
ecosystems (Rai et al. 2005 ; van der Zee and Villaverde 2005 ). Moreover, dyes
have become a health hazard as many of them and/or their breakdown products
have been found to be toxic and potentially carcinogenic (Golka et al. 2004 ;
Pinheiro et al. 2004 ; Schneider et al. 2004 ; van der Zee and Villaverde 2005 ; Chen
2006 ). Physico-chemical treatment processes, such as coagulation, precipitation,

ltration, adsorption, photolysis and oxidation with hydrogen peroxide or ozone,
can generate a large volume of sludge and usually require the addition of other