INTRODUCTION:

Textile industries consume a considerable amount of water in their manufacturing processes. Considering both the volume and the effluent composition, the textile industry is rated as the most polluting among all industrial sectors. Wastewater from textile industries creates a great pollution problem due to the dye content. Textile dye effluents pose environmental hazards because of color and toxicity. Colour is one of the most obvious indicators of water pollution and discharge of highly coloured synthetic dye effluents can be damaging to the receiving water bodies¹.All dyes used in the textile industry are designed to resist fading upon exposure to sweat, light, water, many chemicals including oxidizing agents and microbial attack. The most widely researched fungi in regard to dye degradation are the ligninolytic fungi. White-rot fungi in particular produced enzymes as lignin peroxidase, manganese peroxidase and laccase that degrade many aromatic compounds due to their non-specific activity.

Large literature exists regarding the potential of these fungi to oxidize phenolic, non-phenolic, soluble and non-soluble dyes. In particular laccase from Pleurotus ostreatus, Schizophyllum commune, Sclerotium rolfsii and Neurospora crassa, seemed to increase up to 25% the degree of decolorization of individual commercial triarylmethane, anthraquinonic, and indigoid textile dyes using enzyme preparations² On the contrary, manganese peroxidase was reported as the main enzyme involved in dye decolorization by Phanerochaete chrysosporium³ and lignin peroxidase for Bjerkandera adusta. The most widely studied dye-decolourising microorganisms are the white-rot fungi like Phanerochaete chrysosporium, Trametes versicolor, Coriolus versicolor and Bjerkandera adusta⁴. Several other non-white-rot fungi can also successfully decolorize dyes like Aspergillus niger, Geotrichum candidum ^5,6, Pleurotus ostreatus and Cunninghamella elegans among others. This ability is correlated to the capacity of these organisms to synthesise lignin-degrading extracellular enzymes such as lignin peroxidases (LiP) and manganese peroxidases (MnP), or laccases (Lac)⁷

This study focuses on the biological decolourization of textile effluents through microbial isolates obtained from contaminated sites. The fungal colonies were isolated from the effluent samples and the soil from the contaminated sites. Then the strains with the ability to decolorize the reactive dyes such as Reactive Red 120 and Reactive Black 5 and the microbial decolourization studies were conducted with the strains.

MATERIALS AND METHODS:

Sample collection:

The dye effluent samples and soil sample from the dye contaminated sites were collected from various textile industries such as CETP in SIPCOT, Perundurai, About 3 effluent samples (2 untreated samples and 1 treated sample) and 1 soil sample were collected from CETP, Perundurai. The isolation of Fungal colonies from these samples was then carried out.

Isolation and identification of fungal colonies from the collected effluent and samples:

The fungal colonies are isolated from the effluent and soil samples collected from the CETP in SIPCOT, Perundurai. These are then studied for their ability to decolorize the effluent dyes. The Potato Dextrose Agar (Himedia) plates were prepared and 100 µl of the diluted effluent sample is added to the center of the Potato Dextrose Agar plates and using the L-Rod spread the sample to the whole surface of the Agar plate. The plates were then incubated at 30^oC for 48 hrs. After incubation, pure colony of Aspergillus niger were isolated and screened from a mixture of fungal colonies.

Decolorization studies with Synthetic reactive dyes:

The decolorization studies were carried out for the selected colonies with three synthetic reactive dyes namely Reactive Red 120 and Reactive Black 5. These dyes were prepared at a concentration of 50 mg/ 100ml and the decolorization assay mixture consists of 10% of dye. The decolorization studies were then carried out following the same procedure used for the decolorization of the effluent dyes.

Decolorization studies:

The decolorization studies were carried out for the isolated Aspergillus niger on a specialized media called Bushnell & Haas medium of the following composition (g/l): NH₄NO₃, 0.5; MgSO₄.7H₂O, 0.1; K₂HPO_4,0.5; NaCl, 1g/l; glucose, 10; yeast extract, 2% and pH 6. About a loopful of the inoculum of the Aspergillus niger from the PDA plates is then added to a test tube containing 8 ml of the Bushnell & Hass medium and 1ml of sterilized effluent dye and is then maintained at 37^oC. The samples were withdrawn at 24 hr interval for 7 days and were centrifuged at 10,000 rpm for 15 mins. The Absorbance of the supernatant was measured spectrophotometrically at 572 nm. The dye removal % was calculated after 7 days and the fungal colonies with high decolorization efficiency were selected.

Dye removal (%) was calculated as:

Optimization of decolorization of the synthetic dyes by fungal strains.

The optimization of the decolorization efficiency was then carried out for the fungal colonies. The effect of pH, Temperature, C: N ratio and shaking conditions were studied⁸ and these parameters are optimized to obtain maximum decolorization of the commercial synthetic reactive dyes namely Reactive Red 120 and Reactive Black 5 by using Aspergillus niger.

RESULTS AND DISCUSSION:

Isolation of fungal colonies from the effluent and soil samples

The dye effluent samples and soil samples from the dye contaminated sites were collected from various textile industries such as CETP in SIPCOT, Perundurai. Then isolation of fungal colonies was proceeded. About 8 different fungal colonies were obtained from the samples from CETP, Perundurai.

Fig.1 (a) Effluent sample – 1

Fig.1 (b) Effluent sample - 2

Fig. 1 Fungal colonines from the source CETP Effluent Sample, SIPCOT, Perundurai.

Decolorization of the synthetic dyes using the selected fungal strains

The screened fungal strains were then tested for their ability to decolorize the synthetic dyes. Three synthetic dyes namely Reactive Red 120 and Reactive Black 5 were used for these studies. The synthetic dye removal % of the screened fungal strains is used for further screening. The synthetic dye decolorization studies were made for 8 different fungal strains.

Table. 1 Synthetic Reactive dye removal% of the fungal cultures

Culture Name*	Dye removal % Reactive Red 120 (520nm)(after 7 days of incubation)	Dye removal % Reactive Black 5 (574nm) (after 7 days of incubation)
CETPF1	55.7	44.4
CETPF2	34.8	33.5
CETPF3	24.3	27.4
CETPF4	23.6	17.8
CETPF5	33.6	25.8
CETPF6	65.6	75.8
CETPF7	37.8	28.1
CETPF8	65.4	66.1

* CETPF- CETP Effluent fungal isolates

Based on these studies on the synthetic reactive dye removal by the 8 different fungal cultures, only one fungal isolates selected for the further study on the basis of the high dye removal efficiency of the synthetic reactive dyes.

The following are the different fungal strains that were selected and were renamed as follows,

CETPF 1, 7- Penicillium chrysosporium

CETPF 2,3,4,5 - Penicillium simplicissimum

CETPF 6 - Aspergillus niger

CETPF 8 - Pleurotus ostreatus

Fig.2 (a) Decolorization of Reactive Red 120

Fig.2 (b) Decolorization of Reactive Black 5

Fig. 2 Decolorization of synthetic Reactive dyes by Aspergillus niger

Optimization of the decolorization efficiency for the selected fungal strains

The optimization of the decolorization efficiency was then carried out for the screened fungal strains. The effect of various physical parameters such as Temperature (30, 37, 45°C), pH (3, 4,5, 6), C: N ratio (1:1, 2:1, 1:2) and shaking conditions were studied. The optimum conditions for the decolorization of the synthetic reactive dyes were determined.

Table. 2 Optimization of the decolorization efficiency of Aspergillus niger

Physical parameters	Parameter ranges	% Dye removal Reactive Red 120 (520nm)	%Dye removal Reactive Black 5 (574nm)
Incubation Temperature	30°C	78	40
	37°C	51	35
	45°C	16	22
pH	3	17	06
	4	36	45
	5	56	45
	6	60	61
C:N ratio	1:1	11	14
	2:1	29	52
	1:2	56	85
Culture incubation conditions	Shaking conditions (100 rpm)	78	61
Culture incubation conditions	Static conditions	44	33

Table 2. show the maximum dye removal efficiency (%) of Aspergillus niger was found to occur at the incubation temperature, pH, C:N Ratio and culture conditions is to be 30^oC, 6, 1:2 for the fungal isolate. And the maximum dye removal % occurred at the shaking condition (78 and 61 % of dye removal). Thus, the optimum condition for synthetic reactive dye decolorization by the Aspergillus niger was under the static condition.

CONCLUSION:

The fungal isolates were isolated from the effluent and soil samples from the contaminated sites. They are 8 different fungal isolates were selected. The screened isolates were then tested for their ability to decolorize the two synthetic dyes namely, Reactive Red 120 and Reactive Black 5 and then final screening was done based on these studies. After final screening, only one fungal isolate were selected. The fungal isolates were identified as Aspergillus niger. The various physical parameters such as temperature, pH, C:N ratio, shaking and stationary conditions were optimized for the decolorization of the two different synthetic reactive dyes by the selected Aspergillus niger. This isolated furthorly tested for the ability to decolorize the synthetic reactive dye and it was found that they showed about 65 – 85% dye removal. The fungal isolate were found to degrade the synthetic reactive dyes. It was concluded that the fungal isolates from the samples of the dye contaminated sites showed higher synthetic dye removal per cent age. Thus, the microbial fungal isolate (S) can be used for the decolorization of textile dyes efficiently.

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Received on 25.08.2013 Accepted on 01.09.2013

Research J. Engineering and Tech. 4(4): Oct.-Dec., 2013 page 235-238