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4 Bioremediation of Toxic Dyes for Zero Waste

degradation of remazol red dye [38]. It is reported that the genetically modified

E. coli has shown the decolorization of Direct Blue 71 [39]. It has been reported that

the remazol red dye was degraded with the help of azoreductase gene replicated

from B. laterosporus and incorporated into E. coli [16].

4.4.11

Enzyme-Mediated Dye Removal

The use of different enzymes for the dye degradation is in the initial stages of

growth, but their revolutionary applications are increasingly growing and expand-

ing through all textile processing sectors. According to reports, enzymes from both

anaerobic and aerobic systems can effectively decolorize dyes, and most of the

results come from the white-rot fungi Phanerochaete and Trametes. These species

generate nonspecific extracellular lignin-degrading enzymes (copper-containing

laccases and manganese/lignin peroxidases) which can cleave the azo bond. These

lignin-decomposing enzymes are usually produced by white-rot fungi, when

nutrient levels such as carbon, sulfur, or nitrogen become limited [22]. They are

capable of oxidizing different compounds in large number and are thus intensively

studied in the treatment of effluent from textile industries. White-rot fungi have

shown great potential to degrade azo dyes and related effluents because of the

production of lignin-degrading enzymes. Laccases have tremendous potential for

the bioremediation of these dyes due to their ability to oxidize a wide variety of

substrates. The laccases ability to degrade phenolic compounds makes them ideal

for the degradation of dye effluent containing xenobiotic compounds.

However, before industrial-scale enzyme-mediated dye removal can take place,

there are numerous technical and economic hurdles that have to be addressed.

A significant upstream challenge remains the selection and successful large-scale

strain cultivation for maximum enzyme production. On the other hand, for efficient

fermentation processes, the production of an effective genetic-engineered strain is

crucial. The variables affecting recombinant strain are not well known, despite the

regular use of laboratory-scale cloning, and no industrial-scale process is currently

developed.

4.4.12

Immobilization Techniques

Immobilization of microorganisms or enzymes has been widely documented for the

biological treatment of wastewater. There are different bacterial cell immobilization

methods. Four key groups can be categorized into the vast majority of the methods:

microencapsulation, matrix entrapment, covalent binding, and adsorption. Among

them, due to easy use, low cost, low toxicity to the device, and greater operational

stability, trapping in polyvinyl alcohol gel beads is the strongest.

When applied in a vertical bioreactor system, the immobilized enzymes from T.

versicolor and Pestalotiopsis spp. have been documented to show high decolorization

efficiency. The durability of the beads can be increased by the 0.6% glutaraldehyde

reaction that is necessary for the beads to be reusable. This research indicates that

there is a great potential strategy for the treatment of textile dye effluents for the