当前世界环境

Introduction

In present days, Azo dyes also cause a serious environmental pollution by release of waste water through textile industrial.¹The annual production of azo dyes is estimated to be around one million tons, and more than 2000 different azo dyes are currently in use.²Azo dyes are used in a number of industries such as textile dyeing, food, cosmetics, paper printing, with the textile industry as the largest consumer.³In Textile industry, large amount of water and variety of chemicals are used.⁴The huge amount of water is used in many processes such as cleaning, rinsing, dyeing and washing.⁵Due to use of huge amount of water in textile industries, water layer fall near textile industrial areas. Farmer’s have only option to use polluted water for agriculture and also used in day to day work. Therefore, by using of this polluted water, different types of disease occur in humans as well as in animals.⁶Not only that agriculture crop also affected by this waste water.⁷So, treatment of such waste water could help to meet irrigation requirement of the crops. The discharge of these highly colored industrial effluents is very dangerous when it fall in water resources, as these dyes in the water absorb sunlight, which decreases the intensity of light absorbed by aquatic plants, ultimately reducing photosynthesis and the oxygenation of water reservoirs.^8-9Physical appearance of the colored water gives bad impact on aesthetic value. These dyes are xenobiotic in nature and in some cases, these are mutagenic and carcinogenic.^10-11Allergic effects and health problem in human due to these dyes have also been reported by several scientists^12-15so, Azo dyes contamination has emerged as a serious issue due to negative impact on water ecosystems and human. Different factors也就是说,high water solubility, high molecular weight and fused aromatic ring structures, which reduced degradation of dyes and inhibit penetration in biological cell membranes.^{16日至18日}Various physiochemical methods can be used for the removal of azo dyes from the wastewater.¹⁹Some of these methods are effective but are quite expensive because they generate significant amounts of chemical sludge waste. This chemicals waste causes disposal problem and also limit the use of these methods.^20-22Therefore, in such situations, biological treatment may be a beneficial and being eco-friendly. Microorganisms have developed enzyme system for the decolorization and neutralization of azo dyes under certain conditions.^23-25So, present study was designed to isolate efficient azo dye decolorizaing bacterial strains from the textile effluents. Since the bacterial isolates were originated from the dye contaminated textile wastewater of local industry, so they can easily adapt to the prevailing local environment. Therefore, such bacteria can be used to develop an effective biological treatment system for the waste waters contaminated with azo dyes.

Materials and Methods

Water Sampling

Sampling sites were selected on the basis of outlet drain from textile dying units. 200 samples of Textile waste water (TWW) were collected from areas of Nathnagar of Bhagalpur, Bihar, India nearby many small textile dyeing units are actively operating.

Isolation and Screening of Bacterial Strains

Bacterial strains were cultured from TWW by using MSM agar medium. The culture medium containing 50 ml MSM agar medium was inoculated with 10 ml of TWW then incubated at 35°C for 7 days till the appearance of microbial colonies. 150 actively growing colonies were randomly selected for screening of azo dye decolorizing bacteria and stored in refrigerator for further studies.²⁵

Screening of Azo dye Decolorizing Bacteria

Microbial colonies that appeared on the agar medium were washed gently with sterile water and re-suspended into the flasks containing fresh glucose peptone yeast (GPY) and Hans’s broth media with azo dye at a concentration of 0.1%. The culture media containing 200 ml of GPY and Hans’s broth in 500ml in Erlenmeyer flasks were inoculated with selected bacteria and incubated at 35°C for 36 hrs under static conditions. The respective cells were harvested by centrifugation at 10000 rpm for 10 min then decolorization was determined using spectrophotometer at 596 nm.

Optimization of Different Carbon Source for Enhancement of Decolorization

Carbon sources (charcoal, glucose, fructose, sucrose, maltose, xylose, manitol, cellulose, starch and lactose) at the concentration of 5 gm/L were used for microbial isolates for enhanced decolorization of dyes. Optimization analysis was carried out using broth medium while culture conditions were used in screening of azo dye decolorizing bacteria.

Results and Discussion

Three different bacterial colonies (枯草芽孢杆菌、铜绿假单胞菌Psuedomonas putida) were isolated from TWW.Primary screening of dye decolorizing bacteria was assessed on Han’s medium using different carbon source at the concentration of 5gm/L on 0.1% azo dye. In charcoal carbon source maximum decolorization i.e., 89.0%, 91% and 86% by different bacteria i.e.,枯草芽孢杆菌、铜绿假单胞菌Psuedomonas putidawere observed respectively. In Lactose carbon source minimum decolorization by different bacteria 33.56%, 30.8% and 30.1% were observed respectively in lactose carbon source (Table 1). In GYP medium by using different carbon source (5gm/L) on 0.1% azo dye were used and maximum decolorization by different bacteria 70.23%, 75.0% and 65.0% were observed respectively in charcoal carbon source. Minimum decolorization by different bacteria 32.00%, 30.8% and 34.1% were observed respectively in lactose carbon source (Table 2).

Table 1: Decolorization of azo dye (0.1%) in different carbon source in Hans media.

Table 2: Decolorization of azo dye (0.1%) in different carbon source in GYP media.

Second screening was performed by using Hans medium with Charcoal (5gm/L) carbon source at different time interval incubations to different bacteria也就是说,枯草芽孢杆菌、铜绿假单胞菌Psuedomonas putida.It was observed that maxium decolorization was at 24 hrs time interval by all three bacteria but all of themPseudomonas aeruginosahas maximum decolorization capacity (Table-3). Earlier it was also reported that decolorization of Azo dye occurs by photosynthetic bacteria.²⁶Further the impact of slik dye waste and distillery effluent have also been evaluated on different test animals.^27-28

Table 3: Different percentage of decolorization by different bacteria at different time intervals on Han’s medium.

Conclusion

On the basis of above study, it concludes thatPseudomonas aeruginosais a best decolorizer of Azo dye in Hans’s medium of charcoal carbon source as compare withBasillus subtilisandPsuedomonas putidain GYP medium at 24hrs.

Acknowledgement

The authors are thankful to the Head, PG Department of Biotechnology, T. M. Bhagalpur University Bhagalpur, Bihar for providing necessary research facilities. The authors are also grateful to the Director, University Center of Bioinformatics, T. M. Bhagalpur University Bhagalpur, Bihar for his valuable comments, statistical analysis and funding for this present study.

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