BIOTRANSFORMATION OF TEXTILE DYES: A BIOREMEDIAL ASPECT OF MARINE ENVIRONMENT

Presence of huge amount of salts in the wastewater of t xtile dyeing industry is one of the major limi ting factors in the development of an effective biotreat ment system for the removal of dyes from textile effluents. Large number of textile industries are l ocated on the coastal areas due to ease of transpor t to the various places in world and help in building na tions economy, but on the contrary the effluents released from these industries are proving a great problem for the marine life. Therefore, industrial effluents containing dyes must be treated before th eir safe discharge into the environment. There are various physiochemical methods are conventionally u sed. These methods are effective but quite expensive leading to the production of solid sludge . Bacterial spp. capable of thriving under high sal t conditions could be employed for the treatment of s aline dye-contaminated textile wastewaters. Most of the Scientists used chemical coagulation, Flocculat ion and Precipitation techniques for the removal of dye colors from waste waters. But this method is no t cost beneficial as it generates huge amount of Sludge and to dispose the sludge is major problem. The physical methods are also not cost effective. S o only biological treatment using acclimatized microo rganisms could remove 99-100% dye colour from wastewater. Hence now a day most of the workers con centrated on biotransformation of textile azo dyes by adapted organisms. The use of co substrates also slightly increased the decolorization of dye solut i n. Some scientists showed that the products of dye deg ra ation are not toxic to biological system. Produc ts formed can be determined by Gas Chromatography and Mass Spectroscopy (GC-MS) technique, Fourier Transform Infra Red (FTIR) etc.


INTRODUCATION
Environmental pollution has been recognized as one of the major problems of the modern world. The increasing demand for water and the dwindling supply has made the treatment and reuse of industrial effluents an attractive option. Textile effluents are of concern because they colour the drains and ultimately the water bodies. They also diminish the water quality. The ability of microorganisms to degrade and metabolize a wide variety of compounds has been recognized and exploited in various biotreatment processes.
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. During the dyeing process, a substantial amount of dyes and other chemicals are lost in the wastewater. Estimates put the dye losses at between 10-15% (Vaidya and Datye, 1982). Though

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The textile industries produce effluents that contain several types of chemicals such as dispersants, leveling agents, acids, alkalis, carriers and various dyes (Cooper, 1995). The textile factories daily discharge millions of litres of untreated effluents in the forms of wastewater into public drains that eventually empty into rivers (Olayinka and Alo, 2004). This alters the pH, increases the Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) and gives the water intense colouration (Ajayi and Osibanjo, 1980). The ecosystem is affected.
Several methods are used in the treatment of textile effluents to achieve decolorization. These include physicochemical methods such as filtration, coagulation, flocculation and precipitation. Some of these methods are effective but quite expensive (Do et al., 2002;Maier et al., 2004). Biotreatment offers a cheaper and environmentally friendly alternative for color removal in textile effluents.
Synthetic dyes are used vary widely in many industries such as paper, colored photography and textile industry. There are 10,000 types of dyestuff throughout the world and approximately 7×10 5 tones of these are produced every year. A remarkable amount of the dyestuffs are lost during dyeing processes. These losses are mainly disposed off into aquatic environment by textile and dyeing industries and some others means.
Dark coloured effluents are produced during dye processing which are alkaline and contain organic matters (Zee and Frank., 2002). These effluents impart colour and turbidity not only to receiving body but also to the other water resources in the surrounding areas, due to seepage soil pollution as well as ground water pollution occurs.
Industrial and municipal effluents are often discharged into saline and hyper saline depression and intertidal zones, especially in developing countries (Lefebvre, 2004). The biological treatment of industrial hyper saline wastewaters and the bioremediation of polluted hyper saline environments are not possible with conventional microorganism (Oren, 2002;Pieper and Reineke, 2000).
Conventional microorganisms are unable to operate efficiently at salinities above that of seawater and their capacity of adaptation to salinity is easily lost after exposition to low salinity conditions. High and fluctuating salinity promotes the loss of cell wall integrity, protein denaturaion and changes in osmotic pressure (Pernetti and Di Palma, 2005). Such inhibition effects due to high salinity have been reported in several conventional wastewater treatment plants (Kargi and Dincer, 1997;Woolard and Irvine, 1994). As the salt concentration increases, the microbial diversity is reduced and halotolerant and halophilic species tend to dominate (Oren, 2002). Thus, halophilic microorganisms are potential candidates for the degradation of pollutants at high salt concentration. Kushner (1981) defined halobacteria based on utilization of optimum salt concentration for their growth. In this system, marine bacteria (slight halophiles) grow best at 0.2-0.5 M NaCl.
Azo dyes are released in wastewater generated both by dye producing and dye consuming industries. Biodegradation of azo dyes can occur in both aerobic and anaerobic environments. These compounds are not very susceptible to oxidative metabolisms and as a consequence of this recalcitrance in aerobic environments, these compounds preferentially end up in anaerobic sediments, aquifers and ground waters (Razo-Flores et al., 1997). Rupture of the -N = Ndouble bond leads to the decolorization. Guo et al. (2008a) have described the decolorization of several azo dyes under anaerobic conditions by a new member of the Halomonas genus; strain GTW, isolated from coastal sediments in Dalian Bay (China). Optimal decolorization occurred at 30 o C, pH 6.5-8.5 and NaCl 10-20% with yeast extract as the carbon source. Asad et al. (2007) reported the isolation of three new Halomonas strains from textile effluents that were able to use a wide range of azo dyes as the sole source of carbon. These strains could decolorize the azo dyes in a wide range of NaCl concentrations (upto 20%) and pH (5-11).

History
The history of beautifully coloured compounds (dyes) which make our life colourful and sometimes dark with death goes back over hundreds of years. Dyes have been used since ancient times for colouring and printing fabrics. Untill middle of 19th century, all colorants used were from natural origins, synthetic dye manufacturing started in 1856, when the English Chemist W.H. Perkin in an attempt to synthesize quinine, obtained instead of bluish substance with excellent dyeing property that later became known as Aniline Purple, Tyrin Purple and Mauveine.
The principal route by which the dyes enter the environment is through wastewater. To judge the relative share of different dye classes in the wastewater of textile processing industry, dye consumption data should be considered tighter in the degree of fixation of different classes. The largest class of dye discharged in wastewater by textile industry is Anthraquinone dyes and second largest class is Triarylmethanes.
Indeed, apart from one or two notable exceptions, all the dye types used today were discovered in the 1800's (Gordon and Gregory, 1983). The discovery of the reactive dyes in 1954 and their commercial launch in 1956 heralded a major breakthrough in dyeing of cotton; intensive research in reactive dyes followed over the next two decades and indeed is still continuing today (Gordon and Gregory, 1983).
The concept of research and development was soon followed by the others and new dyes began to appear in the market. In the beginning of 20th century, synthetic dyestuff had most completely supplanted natural dyes (Welham, 2000).

Classification of Textile Dyes
The release of dyes into environment is undesirable not only because of their color but also their breaks down products are toxic or mutagenic to life.
In general, a dye consist of two basic components the chromogen (electron acceptor) and the auxochrome (electron donor) which regulates solubility and dyeing. The chromogen is an aromatic body containing a color giving group called as chromophore. The chromophore causes color by altering absorption bands in the visible region.
Textile dyes are usually classified according to application.

Acid Dyes
The dyes are insoluble in acid the solubility being confirmed by the presence of sulphonic acid group on dyes usually in form of sodium salt. The acidic conditions are used for dyeing of wool and nylon. The three most important classes of acid dyes on basic of chemical classes are Azo, Anthraquinoid and Triphenylmethane.

Azoic Dyes
An azoic coloring matter is a water insoluble azo compound produced in textile fibers. Azoic dyes are used for dyeing cellulosic fibers.

Basic Dyes
These are amino and substituted amino compounds are soluble in acid and become insoluble when alkali is added. They are used as dye acrylics or can be used with a mordant dye for dyeing wool and cotton.

Direct Dyes
Direct dyes are inexpensive and having auxiliary chemicals associated with direct dyeing are sodium salt, fixing agents, metal salts. Direct dyes belong to several chemical classes like Azo, phthlocyanine and stillbene.

Disperse Dyes
A disperses dye is defined as a substantially water insoluble having substantively for one or more hydrophobic fibers. Dyes are used on polyester, polyamide and acrylic fibers.

Fiber Reactive Dyes
Reactive dyes are colored component capable of forming a covalent bond between the dye molecule and fiber. Fiber reactive dyes are mainly used for cotton and cotton blends.

Mordant Dyes
The term mordant dye refers to a dye, which is applied to a fiber in conjunction with metallic mordant. Mordant dyes give fast, full but generally dull shades on wool and nylon.

Sulphur Dyes
Sulphur dyes are used for the dyeing of cellulosic fibers in medium to deep shades of generally dull brown, black, olive, blue, green, maroon and khaki hues.

Vat Dyes
These are water insoluble dyes, which contain at least two conjugated carbonyl groups that enable the dye to be converted into the corresponding water-soluble ionized leuco compound.

Dyes and Environmental Concerns
Textile industries use different colors (dyes) in their processing units. The textile wastewater typically contains the dyes in the range of 10-200 mg L −1 (O'Neil et al., 1999) and therefore usually highly coloured. These dyes in some amount liberated in natural marine water bodies, which in turn affects the marine environment very adversely. The dyes present in the effluent gets mixed the sea water due to which the aquatic life is disturbed. These dyes are toxic so the life in the marine environment is threatened, which affects the quality and quantity of the sea food produced. The release of these dyes in the environment creates an ecotoxic hazard and introduces potential danger of bioaccumulation that may eventually affect man by their magnification in food chain, in successive stages.

Bioaccumulation
The bioaccumulation of the dyes in fish has been investigated in the research promoted by Ecological and Toxicological Association of Dyes and Organic Pigment Manufactures (ETAD). The bioconcentration factors of dyes were determined and it was observed that the water soluble dyes were not bioaccumulated whereas the water insoluble dyes bioaccumulated (Anliker, 1979). Also these dyes being recalcitrant in nature, they are potentially toxic to humans and other life (Yoo, 2000) and if these compounds magnify in the environment and enter the food chain they may endanger sustainability of life on earth.

Dye Removal Techniques
Textile waste can be treated in various ways. This technique includes feasibility of physical, chemical, aerobic, anaerobic, aerobic-anaerobic, biological and combined chemical and biological treatments. During the decolorization processes, it is expected that the system will prevent the transfer the pollution from one part of environment to the other (Vandevivere et al., 1998;Hao et al., 2000;Robinson et al., 2001). Several methods are used in the treatment of textile effluents to achieve decolorization. These include physicochemical methods such as filtration, specific coagulation, use of activated carbon and chemical flocculation. Some of these methods are effective but quite expensive (Do et al., 2002;Maier et al., 2004). Biotreatment offers a cheaper and environmentally friendlier alternative for color removal in textile effluents.
Marine and fresh water, soils and air have been impacted by the dispersion of contaminants. Contamination and biodegradation of the pollutants/contaminants in extreme environments has received little attention although many contaminated ecosystems present high or low temperatures, extreme acidic or alkaline pH, high pressures or high salinity (Margesin and Shinner, 2001).
The characteristics of waste depends on quality of water (Gardinar and Borne, 1978;Norman and Roy, 1991). Type of processing involved and chemicals used. The preliminary processing treatments like sizing, desizing, scouring and bleaching produce effluents having high TDS and high BOD.
Halophilic and halotolerant microorganisms can be the best candidates for a practical biodecolorization process as they are able to grow easily at high concentrations of salts. In recent years, several studies have been focused on halophilic and halotolerant microorganisms and their abilities for decolorization of azo dyes, e.g., Shewanella putrefaciens was determined to be capable of the complete removal of Reactive Black-5, Direct Red-81,Acid Red-88 and Disperse Orange-3 (all 100 mg l −1 ) within 8 h in presence of 40 g L −1 NaCl. Another halophilic example is Halomonas sp. GTW which has shown a remarkable performance in the removal of different azo dyes within 24 h in the presence of 150 g L −1 NaCl (Amoozegar et al., 2011). Park and Choi (1999) studied the treatment ability of an osmotolerant yeast, Pichia guilliermondii A9, for waste brine from a Kim Chi factory using a shaker-flask scale. The growth of Pichia guilliermondii A9 in waste brine was not inhibited by NaCl concentration upto 100 g L −1 .
Marine microorganisms are of immense use in the decolorization of dye because most of the industrial effluents contain high concentrations of salts, especially chlorides and salts. Recently studies have been focused on halophilic and halotolerant microorganisms and their abilities for decolorization of azo dyes which is environmentally benign, cost competitive treatment technology (Amoozegar et al., 2010). Guo et al. (2008a) have described the decolorization of several azo dyes under anaerobic conditions by a new Science Publications AJES member of the genus Halomonas. Asad et al. (2007) reported the isolation of these new Halomonas strains from textile effluents that were able to use a wide range of azo dyes as the sole source of carbon. Guo et al. (2008b) studied the incorporation of biotreatment technology of the Bromoamine Acid (BA) wastewater and azo dye wastewaters under high-salt conditions (NaCl, 150 g L −1 ) in the decolorization of azo dye wastewaters by using halotolerant bacteria grown on BA wastewater and high-salt conditions. Also, studies have been reported that the dye decolorization by facultative and obligate marine fungi viz. Flavodon flavus, Gliocladium sp., Sordaria fimicola, Halosarpheia ratnagiriensis, Algialis grandis, Hypoxylon oceanicum, (Raghukumar, 2000;Raghukumar et al., 2004). Among bacteria, Pseudomonas fluorescens, Pseudomonas aeruginosa, Bacillus subtilis, Bacillus cereus, Proteus vulgaris, Acenetobacter sp., Zooglea sp. are dominant dye decolorizer (Sudhakar et al., 2002).
Marine fungi degrade and remineralize the lignocellulose substrates by their extracellular lignin degrading enzymes. Such fungi were isolated from decaying mangrove wood, leaves, seagrass and algae (Raghukumar et al., 1994). Marine microorganisms are of immense use in the decolorization of dye because most of the industrial effluents contain high concentrations of salts, especially chlorides and salts. Besides, marine microbial enzyme would act efficiently at neutral/alkaline pH and wide range of temperatures to combat the neutral/alkaline dye effluents (Chandramohan, 1997).
Therefore, it may be economical to develop alternative means of dye decolorization such as bioremediation as it is an environmentally friendly, cost effective treatment technology (Hao et al., 2000;Verma and Madamwar, 2003). Microbial decolorization and degradation is an environment friendly and cost effective means to different conventional treatment technologies (Gogate and Pandit, 2004;SalahUddin et al., 2007). Important pollutants in textile effluents are mainly recalcitrant organics, dyes, toxicants and inhibitory compounds, surfactants, chlorinated compounds, pH and salts. Alternations to their chemical structures can result in the formation of new xenobiotic compounds which may be more or less toxic than the potential compounds. It has been proved that dyes have been identified as the most problematic compounds in textile effluents as they are difficult to remove due to their high water solubility and low exhaustion.
The three most common groups are azo, anthraquinone and phthalocyanine dyes (Axelson et al., 2006). Most of which are toxic and carcinogenic (Acuner and Dilek, 2004). Disposal of these dyes into the environment causes serious damage, since they may significantly affect the photosynthetic activity of hydrophytes by reducing light penetration (Aksu et al., 2007) and also they may be toxic to some aquatic organisms due to their breakdown products (Hao et al., 2000).
Dyes can be removed from wastewater by chemical and physical methods including adsorption, coagulation-flocculation, oxidation and electrochemical methods Peng, 1994, 1996). However, both the physical and chemical methods have many shortcomimgs in application, such as high-energy costs, high-sludge production, formation of by-products (Sarioglu et al., 2007). Conversely, bioprocessing can overcome these defects because it is cost saving and environmentally friendly. Fungi (Acuner and Dilek, 2004;Asgher et al., 2008;Jadhav et al., 2007 andalgae (Daneshvar et al., 2007;Mohan et al., 2002) have been used in dye decolorization. Some new bacterial strains capable of decolorizing a broad-spectrum of dyes have also been isolated and characterized (Deng et al., 2008).

Aerobic Biological Treatment
Conventionally activated sludge treatment of wastewater, is often an effective and economic process for reducing organic pollutants in the wastewater. Most synthetic fibers are not readily subjected to extensive biodeterioration but some processing and finishing agents are susceptible to microbial spoilage. Microorganisms can affect all stages of textile processing and storage with fungi being one of the most important microorganisms in textile biodeterioration process (Szostak-Kotowa, 2004).
The occurrence of aerobic conversions of sulphonated azo dyes were more recently reported by Heiss et al. (1992) and Shaul et al. (1991) and sometimes even complete mineralization of a sulphonated azo dye was found used under aerobic conditions. The sulphonated azo dye was used as carbon and energy source in this case (Blumel et al., Science Publications AJES 1998). The degradation of azo dye was also observed in aerobic biofilm rectors, but this also observed in aerobic biofilm reactors, but this also may have been a result of the presence of aerobic microniches in the biofilm (Consterton et al., 1994;Hammer and Bishop, 1992;Jiang and Bishop, 1994).
Recently successful degradation of Acid red 151 as sole source of carbon was described using aerobic sequenced biofilm reactor and mineralization experiments showed that 73% of the carbon was transformed into CO 2 (Quezada et al., 2000). Pagga and Brown (1986) conducted a study on 87commercial-dye stuff. The tests were performed in the reactor designed to stimulate the condition of an adapted activated sludge waste treatment plants.
The highest COD removal efficiency obtained (90%) corresponded to the mixed culture of activated sludge and Halobacter halobium. Kargi and Dincer (2000) conducted a further study with Halobacter halobium. This Species was cultured along with activated sludge in the fed-batch reactor. The organic removal rate was significantly improved COD removal of 85% was obtained within 9 h at high salt contents (3-5%).
In order to estimate the removal efficiency of salt tolerant microorganisms, Kargi and Uygur (1996) used different types of microbial flora, namely Zooglea ramigera and Halobacter halobium. The experiments were conducted using an aerated percolation reactor with 1% salt content.
Anaerobic consortia do generally not degrade the aromatic amines but most of the aromatic amines are readily biodegraded under aerobic conditions (Baird et al., 1977;Brown and Laboureur, 1983). Although for a long time it was thought that azo dyes remained recalcitrant under aerobic conditions, some specific aerobic bacterial cultures were found able to reduce the azo linkage via an enzymatic reaction i.e., azo reductase. Dhavene et al. (2008) studied that the biodegradation of the Diazo Reactive Dye Navy Blue HE 2R by Exiguobacterium spp. upto 91.2% within 48 h in static aerobic condition. He studied the toxicity of the dye on plants viz.Triticum aestivum and Ervum lens linn which are important agricultural crops. The result was that the dye affected the germination process, the growth of plant roots and shoots. Also Kale and Thorat (2010) reported the use of acclimatized aerobic bacteria for the degradation of the dye Reactive Red M5B,which showed complete decolorization and degradation of the dye containing solution.

Anaerobic Biodegradation
Anaerobic reduction of azo dyes using microbial sludges can be an effective and economic treatment process for removing color from dye house effluents. Previous studies have demonstrated the ability of anaerobic bacteria to reductively cleave the azo linkages in reactive dyes (Chinwedkidvanich et al., 2000;Razo-Flores et al., 1997;Loyd, 1992;Ganesh, 1992;Brown and Hamburger, 1987;Brown and Laboureur, 1983;Chung et al., 1992). Bromley-Challenor et al. (2000) reported the decolorization of the azo dye Reactive Red 3.1 (RR 3.1) using unadapted activated sludge incubated under anaerobic condition with 2-70 g L −1 NaCl. In order to biologically treat (e.g., decolorize) commercial reactive dyebaths under hypersaline conditions without dilution, the use of halophilic heterotrophic cultures that can tolerate hypersaline conditions with upto 100 g L −1 NaCl is essential. However, significant decolorization was observed only in 2 g L −1 NaCl containing culture under anaerobic conditions. Some researchers have isolated halophiles from the anoxic sediments of Mono Lake (Blum et al., 2001;Litchfield and Gillevet, 2002). These organisms require salt (especially NaCl) and will not grow if placed in dilute ionic solutions. In addition, other researchers have reported relatively slow and partial bacterial decolorization of phthalocyanine dyes, which is due to their chemical stability and resistance to biotransformation (Nigam et al., 1996;Malpei et al., 1998;Beydilli, 2001;Fontenot et al., 2003). Therefore, the halophilic culture achieved a high degree of dyebath decolorization and could be used for the decolorization and reuse of spent reactive anthraquinone dyebaths.
Several researchers have reported that a range of substituted sulphonated naphthalene derivatives produced by the anaerobic reduction of certain dyes under autooxidation when exposed to oxygen (Nortemann et al., 1994;Kudlich et al., 1997).
Anaerobic digester was much more sensitive to chlorides than activated sludge (Burnett, 1974). Baere et al. (1984) examined influence of high NaCl on methanogenic activity on Anaerobic Filter (AF) process. An anaerobic and aerobic system consisting of an aerobic contactor followed by activated sludge was tested for the biological treatment of high salinity wastewater (Belkin et al., 1993). Feijoo et al. (1995) examined the continous exposure of high salinity in pilot scale USAB and AF Science Publications AJES reactors. The results show that the methanogenic activity of both anaerobic processes was reduced by 50% at sodium concentrations above 20 g L −1 .

CONCLUSION
Bioremediation is the pollution control technology that uses the natural microbial species to catalyse the degradation of variety of toxic compounds. Microbes can acclimatize themselves to toxic wastes and new resistant species develop naturally, which can transform various toxic chemicals to less harmful forms. The results presented here indicated that, the different textile dyes are biodegraded in 24 h by marine isolates. It is also observed that use of Co substrates like 1.0% glucose, 1.0% yeast extract and 1.0% Starch increased the decolourzation and degradation of the dyes.