60

4 Bioremediation of Toxic Dyes for Zero Waste

4.4.8.1

Plant Mechanism for Treating Textile Dyes and Wastewater

Plants can absorb pollutants remaining in the environment through roots, and roots

provide a larger surface area and promote the mobilization, removal, or detoxifica-

tion of pollutants in plants through several mechanisms. Such plant characteristics

have been used to effectively treat the wastes containing phenolic compounds, met-

als, azo dyes and colorants, and numerous other organic and inorganic pollutants

[27]. Information on the dye metabolism mechanism of plants is very limited. Plants

are autotrophic and are believed to absorb xenobiotics during their absorption of

natural minerals and water. In the process of evolution, plants have adapted to adver-

sity mechanisms and enzyme synthesis. Plants mainly remove textile dyes through

adsorption and accumulation, and subsequent degradation is mediated by enzymes

in different parts.

4.4.8.2

Advantages of Phytoremediation

Compared with other physical and chemical remediation methods, phytoremedia-

tion methods to remove the contaminants have the advantage of low cost. This is

mainly because it requires cheaper equipment, is easy to implement, and does not

require personnel to handle it. This phytoremediation technique can be used without

disturbing the location of pollutants.

4.4.9

Integrated Biological, Physical, and Chemical Treatment Methods

In order to better remove the dyes in textile wastewater, combined use of biological,

physical, and chemical treatments may produce encouraging results. This is advan-

tageous because complete degradation is achieved due to the synergetic effect of the

different treatments. Biodegradation and radiation treatment are considered to be

the most suitable methods to remove toxic compounds in natural water. Research

has shown that combining biological methods with physical methods and chemical

oxidation processes will increase efficiency and reduce operating costs. The latest

research on the treatment of textile dye wastewater using combined methods is dis-

cussed in Table 4.5.

4.4.10

rDNA Technology

Synthetic dyes are now produced in such a way that they resist degradation and

become time and effort consuming due to this degradation of dye by conventional

techniques. A big revolution in the area of bioremediation has taken place in genetic

engineering. Under environmental conditions, dye degradation/decolorization may

be enhanced using genetically modified organisms. Functional genes of different

bacterial strains such as Escherichia coli, Sphingomonas desiccabilis, Pseudomonas

putida, Ralstonia eutropha, Mycobacterium marinum, and Bacillus idriensis have

been used to design genetically modified organisms (GMOs) and transferred to

other species [36]. A few studies on the mechanisms of dye decolorization at

the genetic level have been published. Sandhya et al. [37] developed E. coli by

transferring the azoreductase gene from Bacillus laterosporus to E. coli for the