Textile dye industrial effluents are one of great sources of ecological toxicity. It not only affects the quality of drinking water but also has deleterious impact on the soil microflora and aquatic ecosystems [12, 13].
3.1. Isolation and molecular identification of dye degrading bacterial isolates
In the present study, three different bacterial isolates were isolated from textile dye effluent sample. The bacterial isolates were found to be motile, gram negative and rod-shaped strains. The bacterial isolates were molecular identified using 16 s RNA in Sigma Scientific Services Co., Egypt. The identified of bacterial isolate was belonging to Aeromonas aquatic AE 235, Flavobacterium ginsengiterrae DCY55, Shewanella xiamenensis S4 with similarity of 99, 96 and 98% respectively. El Bouraie and Salah El Din [14] reported that the Aeromonas hydrophila isolate can be considered as potential bioremediation for the treatment of dye industrial wastewater. Xu et al. [15] have investigated isolation of Shewanella decolorationis S12 for the ability of dye decolourization.
3.2. Screening of dye decolorizing bacterial isolates using plate technique
In the present study, three bacterial strains were screened for potential decolourization of textile dyes effluent sample was achieved by plate assay [16]. The selected bacterial strains were tested separately and consortium of all for their ability to decolorize dye wastewater sample and the results were tabulated in Table (1). The bacterial strains exhibiting strong decolourizing activity were also reported by Hassan et al. [17]. The maximum percentage decolourization was recorded by mixture of three tested strains in the plate containing dye effluent sample as zone inhibition, followed by Shewanella xiamenensis, Flavobacterium ginsengiterrae and Aeromonas aquatic after 24 h. Karthikeyan and Anbusaravanan [18] reported the isolation and screening of microorganisms able to decolourizing diverse azo dyes from wastewater treatment sites polluted with dyes. Azo-dyes were degraded by extracellular peroxidase released by Falvobacterium sp [19].
Cell walls consist fundamentally of polysaccharides, proteins and lipids exhibit abundant functional groups. The dyes can interact with these active groups on the cell surface in a different manner. So, the degradation efficiency of dyes by microbial biomass is due to ion-exchange mechanisms [20]. Many researchers have mentioned that a higher degree of biodegradation and mineralization of textile dye effluents can be expected when co-metabolic activities within a microbial community supplement each other. In such a ‘consortium’, the organisms can act synergistically on a variety of dyes and dye mixtures. One organism may be able to cause a biotransformation of the dye, which consequently renders it more accessible to another organism that otherwise is unable to attack the dye [21].
3.3. Dye decolourization assay by bacterial strains
The bacterial strains degrade the industrial textile effluent as their energy source. Many authors have isolated several microbial strains having potential to decolorize a large number of dyes [22]. Biological decolourisation has been determined as a method to transform, degrade, or mineralize of dyes. Moreover such decolourization and degradation is an environmental friendly and cost competitive alternative to chemical decomposition processes [23].
The bacterial strains and its consortium were tested for their ability to decolorize the effluent dye textile sample. The percentage decolourization by bacterial strains was measured spectrophotometrically. The different percentage of degradation of textile dye effluents was noted in Fig. 1. The results suggested that, all the bacterial strain was able to decolorize the dye sample. The maximum biodegradation of dye was observed in culture media containing bacterial consortium at 98% followed by Shewanella xiamenensis at 95%, Flavobacterium ginsengiterrae at 94% and Aeromonas aquatic at 90% after 24 h of incubation time. Ogugbue and Sawidis [24] were describing the isolation and characterization of a strain of Aeromonas hydrophila capable of efficiently degrading triarylmethane dyes. The strain Aeromonas hydrophila was shown to decolorize three triarylmethane dyes tested in the range of 72 to 96% within 24 h. El Bouraie and Salah El Din [14] illustrated that the decolourization efficiency of Reactive Black 5 dye by Aeromonas hydrophila was obtained to be 76% at 100 mg L− 1 within 24 h.
Higher degree of biodegradation and mineralization can be expected when co metabolic activity within a microbial community complement each other. One organism may be capable of cause a biotransformation of the dye polluted which consequently it more attainable to another organism that else is unable to attack the dye. Similar results were reported by Mahmood et al. [25] the bacterial consortium exhibited a remarkable increase in dye degradation and decolourization. The consortium decolorized range from 89 to 94% of different types of dyes within 24 h incubation.
3.4. Evaluation of dye decolourization
The degradation efficiency of isolated bacterial strains was determined by spectrophotometric assay. Comparison of FTIR spectrum of control textile dye effluent (before degradation) with FTIR spectrum of dye culture supernatant after decolourization clearly indicated the biodegradation of the dye by pure bacteria and its consortium strains (B1, B2, B3, BC) (see Fig. 2). The FTIR spectrum of the control dye displayed a peak at 2921.98 cm− 1 indicates the C–H stretching of alkanes while the specific peak at 1699.69 cm− 1 was attributed to the N = N stretching vibrations of the azo bonds position. The peaks at 1540.89 cm-1 for aromatic C = C stretching supported the aromatic structure of the dye. While the presence of peak at 1057.10 cm− 1 suggested stretching vibrations of primary alcohols C–OH. The FTIR spectrum of dye culture supernatant after decolourization showed diversity in the positions of peaks when compared to control dye spectrum. Absence of the peak 2921.98 cm− 1with bacterial consortium and appeared new peak at 1426.03 was due to C-H deformation of alkanes. The disappearance of peak at 1699.69 cm− 1 indicated the cleavage of dye at azo bond position in all bacterial culture that would be an essential step for color removal. On the other hand, absence of peak at 1540.89 cm− 1 with B1 and bacterial consortium suggested cleave of aromatic rings. Further, new peaks around 3800 − 3100 cm− 1 represented the amides, amines and carboxylic acid (–OH,-NH-, =C-H) of all different types of bacterial culture. The stretching vibration between –N– C = was detected at 1426–1455 cm− 1 with B1, B3 and BC. In addition, peaks at 1339.92 and 1246.75 cm− 1 were attributed to stretching vibrations of S = O and O–NO2 vibration of nitrates respectively of bacterial culture B2. Meanwhile, the new peaks (668–880 cm− 1) indicated the fission of aromatic rings. From the FTIR spectra, it may be concluded that the different bacterial strains and bacterial consortium decolorizes textile dye effluent attributed to biodegradation process [26].
3.5. Physico-chemical properties of textile dye after biodegradation
The industrial wastewater sample which collected from located studied. This industry discharges the pinky color effluent with dye and toxic compounds into the open environment. The physico-chemical characteristics of collected sample and after biotreatment by consortium of three bacterial strains were listed in Table (2) with standard methods of USA, 1995 and according to the allowable limit of Ministerial Resolution no. 44, 2000. The data in Table 2 was illustrated that temperature recorded in wastewater and treated samples at 25 °C which lower than the permissible limit. The pH value was recorded at 8.2 and 7.3 before and after biotreatment respectively. The pH was alkaline in nature and samples have pH within the permissible limit also reported Manikandan et al. [27]. The electrical conductivity was reduced in biotreatment sample at 800 µ.s. Electrical conductivity is commonly used as a measure of salinity of waste water. The value of total dissolved solid was obtained from dye wastewater sample 7400 mg/l which reduced into 500 mg/l in biotreated sample. High concentration of dissolved solids affects the density of water and influences solubility of gases in water (like oxygen) and osmoregulation of freshwater organisms [28]. Dos Santos et al. [29] illustrated that the presence of dyes in textile effluent contributes to high levels of suspended solids (SS), high chemical oxygen demand (COD) and biological oxygen demand (BOD). The total suspended solids were recorded at 20 mg/l in biotreated sample which lower than the dye wastewater sample. The bacterial consortium was reduced the chemical oxygen demand at 250 mg/l its effect on the quality of freshwater and subsequently cause harm to aquatic life [28]. The biological oxygen demand was recorded at 4000 mg/l which reduced into 200 mg/l with bacterial consortium, the COD and BOD which above the recommended global level [30]. The phosphate, nitrate and sulfide contains were recorded lower than the permissible limit in all different sample. The Phosphate and nitrate are major nutrients needed by living microorganisms for their physiological processes in ecosystem. However, they are considered as pollutants if their concentration is more than recommended limit.
Table 1
Screening of different bacterial strains for dye degradation by plate assay
Code of microorganisms | Name of bacterial strains | Zone information (in mm) |
B1 | Aeromonas aquatic AE 235 | 2.2 |
B2 | Flavobacterium ginsengiterrae DCY55 | 2.4 |
B3 | Shewanella xiamenensist S4 | 2.5 |
BC | Bacterial consortium from three strains | 3.0 |
Table 2
Physico-chemical properties of textile dye effluent sample and after treatment by bacterial consortium
Experiments analysis | Dye effluent sample | Dye sample after biological treated | Allowable limit |
Temperature oC | 25 | 25 | 43 |
pH | 8.2 | 7.3 | 6-9.5 |
Suspended soiled (mg/l) | 111 | 20 | 800 |
T.D.S. (mg/I) | 7400 | 500 | 2000 |
B.O.Ds | 4000 | 200 | 600 |
C.O.Ds | 9000 | 250 | 1100 |
Conductivity (µ.s) | 12500 | 800 | 4000 |
Phosphate (mg/l) | 2.64 | 0.5 | 25 |
Nitrate (mg/l) | 52 | 20 | 100 |
Sulfide (mg/l) | 1.48 | 0.4 | 10 |
Oil& Grease | 20 | 3 | 100 |
Color | Pinky | Colorless | Colorless |
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