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4 Bioremediation of Toxic Dyes for Zero Waste

iii. Composting: This is an anaerobic and high-temperature treatment process in

which contaminated substances are mixed with fillers.

iv. Bioventing: This method treats contaminated soil by supplying oxygen to stim-

ulate microbial activity.

v. Biofilters: In this method, a microbial stripper is used to treat air emissions.

4.4.2

Microbial Remediation

Microorganisms already exist in wastewater treatment feeds, and the complex

substances in it will be converted into their simpler forms, thereby improving

the treatment effect. Nowadays, biological treatment is a common technology for

dye wastewater treatment. Several reports indicate that a large number of species

have been used to remove and fully mineralize different types of dyes. The main

advantages of this method are cheap, low operating cost, and nontoxic final product.

However, these processes may be aerobic, anaerobic, or a combination of aerobic

and anaerobic. Bacteria and fungi are commonly used in aerobic treatment due to

their ability to treat dye wastewater [4].

4.4.2.1

Aerobic Treatment

In aerobic treatment, enzymes secreted by bacteria present in wastewater decom-

pose organic compounds. Since more than two decades, the work of identifying and

isolating aerobic bacteria that can degrade various dyes has been ongoing. Kurthia

sp. has been discovered to effectively decolor (92–100%) various triphenylmethane

dyes such as malachite green, crystal violet, magenta, ethyl violet, and brilliant

green. Since the past two decades, various researchers have conducted extensive

studies on Phanerochaete chrysosporium among various fungi to enable it to

decolor many dyes. In addition, the microbial decolorization using Rhizopus oryzae,

Corio cyanobacteria, Trichoderma harzianum, Laetiporus thiourea, Streptomyces,

and Aspergillus multicolor was also tested. In order to improve the treatment of

dye effluents, the treatability of wastewater by other microbes can be improved.

Obviously, these techniques are applicable to certain dyes. However, most dyes are

resistant to biodegradation or cannot be transformed under aerobic conditions [4].

4.4.2.2

Anaerobic Treatment

Anaerobic effluent treatment is quiet promising and can well prove and establish

methods to degrade many synthetic dyes. Since the past few decades, it is reported

that the mordant granular sludge can reduce and decolorize azo orange 1 and

azo disalicylate in anaerobic environment. Another study proved the possibility

of using anaerobic granular sludge to completely decolorize 20 azo dyes. The

anaerobic pretreatment is inexpensive alternative when compared with the aerobic

system because it does not require expensive aeration and can avoid the problem of

sludge expansion. Researchers have certainly reported that the anaerobic effluent

treatment can be effectively performed to remove dyes [4].

4.4.2.3

Aerobic–Anaerobic Treatment

So as to achieve better removal of dyes from textile effluent, the combination of aer-

obic and anaerobic treatment may bring encouraging results. This is advantageous