4.4 Bioremediation Methods

55

Table 4.2

Bacterial species reported as dye degraders.

Sl. no.

Degraded

dye(s)

Bacteria

Percentage removal

of dye at 100 mg/l

concentration (%)

1.

Novacron super black G

Alcaligenes faecalis

90

2.

RY107, RB5, RR198, and

DB71

Brevibacterium spp.

99

3.

Direct red-22

Bacillus cohnii

95

4.

RV-5R and RBO-3R

Bacillus spp.

63.33, 96.15

5.

Orange 10

Pseudomonas putida

70

6.

Malachite green

Enterobacter spp.

100

7.

Yellow 107

Staphylococcus arlettae

99.5

8.

Synazol red 6HBN

Alcaligenes aquatilis

82

9.

Crystal violet

Aeromonas hydrophila

99

10.

Direct red 81

Enterococcus faecalis

100

11.

RO-16, DB-19

Acinetobacter junii

90

12.

Acid red 337

Bacillus megaterium

KY848339

98.9

13.

Reactive red 198, Congo red

Acinetobacter baumannii

>95

14.

Reactive red 35, 198, 106,

120, 111, 141, and 152

Reactive black 5

Reactive blue 160 and 28

Enterococcus gallinarum

>91

Source: Paba et al. [12]; Hossen et al. [13]; Roy et al. [14]; Ayman et al. [15]; Ajaz et al. [16].

nitrogen, electron donor, soluble salts, and redox mediator, can highly affect the

bacterial degradation of different toxic dyes. Therefore, the growth of industrial

bioreactors demands that these abiotic conditions should be optimized.

pH of the Medium Due to the dependence of enzyme activity on pH, the pH of the

medium is one of the most important factors in the microbial decolorization of dye.

The pH of the dye effluent can be alkaline, acidic, or neutral depending on the type

of dyes and salts used. Often, at neutral pH, the efficiency of bacterial decolorization

is stronger and a pH between 6.0 and 10.0 is optimal for color removal. The color

removal rate is highest at optimum pH, and at highly acidic or highly alkaline pH it

is likely to decrease. This problem can be solved by (i) changing effluent pH to help

dye degrading bacteria growth or (ii) choosing microbial species which can grow at

the pH of the effluent. It is considered that the movement of dye molecules across

the cell membrane is correlated with pH change and this may affect their transport,

which is a rate-limiting step for the decolorization process.

Effect of Temperature Another essential element involved in the bacterial decoloriza-

tion of dye is temperature, which can affect the growth of bacteria and enzyme