INTRODUCTION:

The waste synthetic dyes from different sources, for example, material, paper, pharmaceutical industry, tannery industries add up into our regular water resources or waste water treatment units. One of the main sources with stern contaminating issue worldwide is the textile industry and its waste waters containing dyes. During dying process and 2-20% are directly discharged as aqueous effluents in different environmental components ¹.

The discharge of effluents containing dyes into water is undesirable due to its colour, dyes released and the breakdown products of dyes which are toxic, carcinogenic to life mainly because of the presence of carcinogens present such as naphthalene, benzamine and other aromatic compounds. If not treated these dyes remain in the environment for a long period of time ^{2, 3}. Another big issue is, the textile industry consumes large amount of water. So recycling of treated waste water should be done due to the high levels of contamination in dyeing and finishing process. Due to the toxic nature and adverse effect of synthetic dyes on environment the move to natural dyes started worldwide. But due to the use of mordents e.g. chromium to fix color on to the fabric they may be very toxic and render waste water poisonous. Natural dyes also require comparatively large quantity of water. Also about 80% of the dye stuff only stays on the cloth rest drain out even natural dyes high impact on the environment⁴.

CLASSIFICATION OF SYNTHETIC TEXTILE DYES:

The natural textile dyes were basically utilized for coloring fabric, until the 1856 utilizing colors extricated from vegetable and animals. The synthetic dyes were found in 1856. These dyes consist of aromatic compounds containing aromatic rings that contain delocalized electrons and unique functional groups. The color of the dye is due to the chromogene-chromophore i.e. acceptor of electrons, in the molecule of dye, and the dyeing capacity of the dye is due to the presence of auxochrome groups i.e. donor of electrons. The chromogene is an aromatic structure which normally contains benzene, naphthalene or anthracene rings carrying binding chromophores that contain double conjugated links with delocalized electrons forming conjugated systems. The groups which mainly act as chromophores are the azo group (-N=N-), methine group (-CH=), ethylene group (=C=C=), carbonyl group (=C=O), carbon-sulphur (=C=S; ≡CS-S-C≡), nitro (-NO2; -NO-OH), nitrozo (-N=O; =N-OH), carbon-nitrogen (=C=NH; -CH=N-), or chinoid groups. The auxochrome groups are ionizable groups, which are responsible for the binding capacity of the dyes molecules onto the textile material. The common auxochrome groups are: -COOH (carboxyl), -NH2 (amino), -SO3H (sulphonate) and -OH (hydroxyl) ⁵.

STRUCTURE OF SOME OF THE COMMON DYES:

The Textile dyes are mostly categorized in two ways:

(1) in view of its application for example, mordant, reactive, disperse, acid, basic, direct, sulphur dye, pigment, vat, azo insoluble dye.

(2) in light of its chemical structure, for example, nitro, azo, carotenoid, , acridine, quinoline, indamine, xanthene sulfur, diphenyl methane, indigoid, anthraquinone, amino-and hydroxy ketone, phthalocyanine, inorganic pigment, and so on.

The synthetic textile dyes are also categorized as anionic, nonionic and cationic dyes based on their general structure.The major nonionic dyes (which do not get ionized in the aqueous medium) are disperse dyes, and the major cationic dyes are the azo basic, anthraquinone disperse dyes.

TECHNOLOGY OF TEXTILE PROCESSING:

The common textile processing technology comprises various steps such as desizing, scouring, bleaching, mercerizing and dyeing processes (EPA, 1997) ⁶:

Sizing is the first preparation step, which involves addition of sizing agents such as polyvinyl alcohol (PVA), starch and carboxmethyl cellulose to impart strength to the fibres so as to lessen breakage.

Desizingis the process used to remove sizing agents prior to weaving.

Scouring is the process in whichimpurities are removed from the fibres by treating them with alkali solution usually sodium hydroxide to breakdown natural oils, fats, waxes and surfactants.

Bleachingis the step in which unwanted colour is removed from the fibers by treating with chemicals such as sodium hypochlorite and hydrogen peroxide.

Mercerising is a step in which a concentrated alkaline solution is applied to the fabric that is then washed using an acid solution fibres prior to the dyeing step. Mercerising increases the dye-ability, lustre and appearance of the fibre.

Dyeingis the process which involves the addition of colour to the fibres. It usually needs large volumes of water in the dye bath as well as during the rinsing step.

Depending on the nature of the fabric, various chemicals for example surfactants, metals, salts, sulphide, organic processing aids and formaldehyde, can be added to enhance the adsorption of dye onto the fibres in the dyeing process.

FIXATION DYE OF ON TEXTILE FIBRES:

In general, textile fibres can catch dyes in their structures as a result of physical adsorption which involves van der Waals forces, hydrogen bonds and hydrophobic interactions between the fibre and dye. The binding of the dye in fibres depends on nature and chemical constitution of the dye. The strongest dye-fibre attachment occurs due to chemisorption which involves the formation of a covalent bond along with an additional electrostatic interaction when the dye ion and fibre carry opposite charges. In alkaline conditions i.e. pH 9-12 , at 30-70ºC temperatures with 40-100 g/L salt concentration, reactive dyes form a reactive vinyl sulfone (─SO₃─CH═CH₂) group, which forms a bond with the fibres. But vinyl sulfone (─SO3─CH═CH2) group, which makes a bond with the fibres, experiences hydrolysis if water is present and the products obtained don't have any attraction with the fibres hence they don't make a covalent bond with the fibres. Thusly, a lot of the color is washed away in the wastewater.The fixation efficiency varies with the class of azo dye used, and it is about 98% for basic dyes and 50% for reactive dyes ⁷. Large amounts of salts such as sodium nitrate, sodium sulphate and sodium chloride are used in the dyebath. Sodium hydroxide is extensively applied to increase the pH to the alkaline range.

Fixation degreeof different dye classes on textile support (EWA,2005)⁸

Dye class	Fibre type	Fixation degree, %	Loss in effluent, %
Basic	Acrilic	95-100	0-5
Acid	Polyamide	80-95	5-20
Disperse	Polyester	90-100	0-10
Direct	Cellulose	70-95	5-30
Reactive	Cellulose	50-90	10-50
Sulphur	Cellulose	60-90	10-40
Metal complex	Wool	90-98	2-10

The issues of huge effluent rich in waste dye stuff has been recognized primarily with the dyeing of cellulose fibres mainly with the application of reactive dyes (10-50% loss in effluent), sulphur dyes (10-40% loss in effluent), direct dyes (5-30% loss in effluent), and vat dyes (5-20% loss in effluent). The need of the hour is to develop such techniques for the textile coloration industry production that minimise wastage of dye and hence reduce colour loads in the effluent by optimising the processes, and controlling automatically the dyeing and printing operation.

CHARACTERISATION OF SYNTHETIC TEXTILE DYES:

Colour in wastewater is categorized as true or real colour i.e. colour water sample without turbidity, or apparent colour i.e. colour of untreated water sample. The common methods used to measure the colour of dye solution or dispersion or waste water are visual comparison and spectrophotometry.

By visual comparison method:

Intensity of the colour is measured or predicted by comparing the colour of sample (textile waste water) with either known concentrations of coloured standard solutions generally a platinum-cobalt solution, or accurately calibrated colour disks. This method is not much applicable for highly coloured industrial wastewaters.

Another method used is the spectrophotometric technique, in which colour estimating methodology differ between the procedures and of the most regularly utilized are Tristimulus Filter Method, American Dye Manufacturer Institute (ADMI) Tristimulus Filter Method, and Spectra record.⁹

Tristimulus Filter:

In tristimulus Filter three tristimulus light filters are put between the light source, for example, tungsten lamp and a photoelectric cell inside a filter photometer. The transmittance is converted to trichromatic coefficient and value characteristic of colour.

ADMI Tristimulus: The ADMI colour value offers a true watercolour measure, which can be distinguished in 3 (WL) ADMI, the transmittance is determined at 590, 540 and 438 nm or 31 (WL) ADMI, the transmittance is recorded at each 10 nm in the range of 400-700 nm.

Spectra record:

In this method a complete spectrum of the sample textile waste water is recorded and the entire spectrum, or a part of spectrum is compared. In the modified method the areas under an extinction curve gives the colour intensity.

ENVIRONMENTAL IMPACT OF SYNTHETIC TEXTILE DYES:

High concentration of dyes in water bodies stop the oxygenation capacity of the receiving water and cut of sun light thus upsetting the biological activity of aquatic life and photosynthesis process of aquatic plants such as algae, The blue, green or brown colours of water courses is accepted by public but the red and purpide colors in water bodies make people concern. Polluting effects of these dyes is also due to their non-biodegradability, they keep on accumulating in the sediments, in fishes or other aquatic life forms. Decomposition of dyes into pollutants in carcinogenic or mutagenic compounds causing allergies, skin irritation, or different tissue changes¹⁰. Azodyes which are aromatic compounds cause high potential health risk by adsorption of azodyes and their breakdown products like toxic amines through the gastrointestinal tract, skin, and lungs and also formation of hemoglobin adducts. Several Azodyes cause damage of DNA which leads to malignant tumors. Carcinogenic potential of the dye increase when electrodonoting substituents are present in ortho and para position. Toxicity can be reduced with protonation of amino groups. The azodyes such as direct black 38, azodisalecylate and their breakdown derivatives like bezidine, its derivatives, a large number of anilines nitro semis, dimethyl amines etc. are known to induce cancer in human and animals ¹¹. Some azodyeds have been linked to bladder cancer in humans, splenic aromas, hepato carcinomas and nuclear anomalies like chrosomal aberration in mammalian cells ¹². The dyes which are made from known carcinogens such as benzidine and other aromatic compounds are reported as the most problematic dyes. Anthroquinone-based dyes because of their fused aromatic ring structure are resistant to degradation. There is evidence that malachite dye has adverse effect on immune and reproductive systems. It is also a geno toxic and carcinogenic agent. CI dispose of blue dye has genotoxic and cytotoxic effects on human cells. It also causes DNA fragmentation.

METHODS FOR REMOVAL OF SYNTHETIC TEXTILE DYES FROM WASTE WATER:

The organic dyes must be separated and eliminated from water by effective and viable treatments at sewage treatments works or on site by trying to remove, degrade neutralize the harmful pollutants so as to neutralize the harmful effects of industrial effluents. They have detergent, surfactants, weakly biodegradable substances suspended solids along with unused dyes. Due to diverse chemical nature of textile effluents, they are difficult to treat by conventional purification procedures. Treatments like chlorination cannot be used as it release mutagenic products even from less harmful dyes.

PHYSICAL METHODS FOR REMOVAL OF ORGANIC DYE POLLUTANTS FROM WASTE WATER:

Adsorption:

Adsorption has been found to be one of the most effective and established treatment of wastewater in textile industry as it is an economically achievable process for dyes removal and/or decolourization of textile effluents. The process involves the transfer of soluble organic dyes from wastewater to the surface of the adsorbent which is solid and highly porous material. The adsorbent adsorbs each compound to be removed to its capacity and when it is ‘spent’ should be replaced by fresh material. The spent adsorbent may be either regenerated or incinerated The principle factors which impact dye adsorption are: attraction between dye and adsorbent, surface area and molecular size of adsorbent, pH , temperature and time duration of contact. The most normally utilized adsorbent is activated carbon. Activated carbon has been built for ideal adsorption of big, negatively charged or polar particles of dyes.

Powdered or granular activated carbon with specific surface area of 500-1500 m2/g; pore volume of 0.3-1 cm3/g; bulk density of 300-550 g/L has been observed to have a practically good colour removal capacity if it is used in a separate filtration step.The cationic mordent and acid dyes are eliminated with high expulsion rates ¹³, while dispersed, vat, direct, pigment and reactive dyes are eliminated with temperate elimination rates ¹⁴.

Bio sorption has been considered utilizing different more affordable adsorbents of agricultural wastes like rice husk, sugarcane, bagasse, and corncobs etc. or industrial wastes such as coalashes, peat, clay, bentonite, red soil, bauxite,rice husk, leaf powder, wood chips, ground nut shell powder, ricehusks, bagasse pith, wood sawdust, other ligno-cellulosicwastes, etc. which can soak and collect dyes and other organic compounds from textileeffluents with an elimination capacity of 40-90% basic dyes and 40% direct dyes ^{15,16, 17,18}. The benefit of utilizing these materials is primarily because of their extensive availability, low cost and no need for their regeneration.

The ‘spent’ material isusually burnt though there is potential to use it for proteinenrichment by its solid state fermentation.Though the use of ‘low cost’ adsorbents for textile dye removal is lucrative but a vast amount of adsorbents are required as these are less efficient than activated carbon^{19, 20, 21, 22}.

Irradiation:

The irradiation treatment involves the use of radiations usually obtained from a monochromatic UV lamps working under 253.7 nm. It is a simple and effective technique for removing a wide variety of organic contaminants, and disinfecting harmful microorganism.The irradiation treatment includes the utilization of radiations generally got from a monochromatic UV lamps working under 253.7 nm. It is a basic and viable method for eliminating a wide range of contaminants, and harmful microorganism. This method needs a constant and adequate supply of oxygen because a large amount of dissolved oxygen is required for effectively breaking down of an organic dye by irradiation. Irradiation treatment of a secondary effluent from sewage treatment plant has been observed to reduce COD, TOC and colour up to 64%, 34% and 88% respectively using a dose of 15 K Gy gamma-rays ²³. The efficiency of irradiation treatment can be increased by using catalyst titanium dioxide ²⁴.

FILTRATION PROCESSES:

These are new procedures, which may be used to check organic contaminants andmicroorganisms present in wastewater. The common membrane filtration types are:

Micro-filtration:

It is generally utilized for treatment of dye baths containing shade pigment dyes and for following rinsing baths²⁵. Suspended solids, colloids from effluents or macromolecules with particle size of 0.1 to 1 micron get eliminated by microfiltration so microfiltration might be utilized as a pre-treatment for nano filtration or reverse osmosis²⁶. MF is effective in removing about 90% of turbidity or silt. Microfiltration membranes are made from polymers such as Poly (Ether Sulfone), Poly Tetrafluoroethylene (PTFE), Poly (Vinylidiene Fluoride), Poly (Vinylidene Difluoride), Poly (Sulfone), Polypropylene, Polycarbonate, etc. When extraordinary chemical resistance or high temperature is required in the operation, ceramic, glass, carbon, zirconia coated carbon, alumina and sintered metal membranes are used. Usually MF and UF operate at 20 to 100 psi transmembrane pressures (Ptm) and velocities of 20 to 100 cm/s ²⁷.

Ultra-filtration:

This technique can removepolluting substances such as dyes only 31-76% but can be used to eliminatemacromolecules and particles. The treated wastewater cannot be reused for sensitive processes, such as textile dyeing ²⁵ but can be used for rinsing, washing, etc. Ultrafiltration is used as a pre-treatment for reverse osmosis (28) or to remove metal hydroxides ²⁸. UF membranes are made from polymers such as nylon-6, polytetrafluoroethylene (PTFE), polyvinyl chlorides (PVC), polysulfone, polypropylene, acrylic copolymer etc.

Nano-Filtration:

It is utilized for the treatment of coloured effluents from the textile industry, for the most part in a mix of adsorption and Nano-filtration as NF modules are extremely sensitive to fouling by colloidal material and macromolecules. NF membranes are ordinarily produced using cellulose acetate and aromatic polyamides. Inorganic materials, for example, carbon based membranes, ceramics, zirconia can likewise be utilized as a part of making NF and RO membranes. These can remove low-molecular weight organic compounds, large monovalent ions, divalent ions, hydrolysed reactive dyes, and dyeing auxiliaries. About 70% colour removal has been reported for a NF plant working at 8 bar/18°C, with four polyethersulphonate membranes with molecular weight cut offs of 40, 10, 5 and 3 kda for three distinct effluents from colouring cycle of textile industry ²⁹. NF treatment can be sensibly utilized as an option for decolourization of textile effluent.

Reverse Osmosis:

This techniqueis used to eliminate hydrolysed reactive dyes, most types of ionic compounds, chemical auxiliaries in a single step. The influent has to be very carefully pre-treated because RO is very sensitive to fouling like NF. RO membranes are usually made from cellulose acetate and aromatic polyamides and of some inorganic materials.

The choice of the membrane process depends upon the nature of the final effluent.The membrane methods combined with physio-chemical treatment have advantages over the other traditional procedures, for example their capability to recover dye materials from industrial effluents, along with recyclable water, so as to reduce the consumption of fresh water and costs for wastewater treatment. As a result there are small disposal volumes of waste which minimizes the costs of waste disposal etc. The major difficulty with physical method is the huge sludge production. So disposal of solid adsorbent itself becomes a big headache. However physical methods are useful when effluents volume is small.

CHEMICAL METHODS OF REMOVING DYE FROM WASTE WATER:

OXIDATIVE PROCESSES:

Chemical oxidation is the conversion of pollutants by chemical oxidising agents (such as chlorines, ozone, Fenton reagents, UV/peroxide, UV/ozone etc.) other than oxygen/air or bacteria to similar but less harmful compounds and to easily biodegradable organic compounds.

Oxidation with sodium hypochlorite:

Inthis treatment azo-bond cleavage is initiated and accelerated by the attack of the dye molecule by Cl⁺at the amino group. The dye elimination and decolourization process gets accelerated with the increase in the concentration of chlorine which reduces the pH of effluent. /The chlorine decolourization works best on dyes which contain naphthalene ring with amino or substituted amino groups i.e. dyes derived from amino-naphthol-and naphtylamino-sulphonic acids (Omura, 1994). However this method is not suitable for removal of disperse dyes. Due to negative effects of aromatic amines or other toxic molecules on releasing these into water resources, this method is less frequently used.

Oxidation with hydrogen peroxide:

The oxidation processes with hydrogen peroxide (H₂O₂) can be used as wastewater treatment in two systems:

(1) Homogenous systems based on using visible or ultraviolet light, soluble catalysts, for example, Fenton reagents( hydrogen peroxide activated by some iron salts without UV light to produce hydroxyl radicals (HO.) which are solid oxidants than H₂O₂ and other chemical activators, for example, ozone, peroxidise etc. The efficiency of the Fenton oxidation treatment mainly depends on characteristics of the effluent and working conditions e.g., 31.5 % colour removal has been reported for effluents containing Remazol Arancio 3R, Remazol Rose RB textile dye, by Fenton oxidation at a pH of 4.00, utilizing 0.18-0.35 M H₂O₂ and 1.45 mM Fe2+, after 30 min. of oxidation.³⁰

(2) Heterogenous systems based on using semiconductors, zeolites, clays with or without ultraviolet light, e.g. TiO2, modified zeolites with iron and aluminium lead to colour removal of 53-83%, COD removal of 68-76% and TOC removal of 32-37% have been reported in the dye-containing effluents by heterogenous catalytic oxidation using 20 mM H₂O₂ and FeY11.5 (1 g/L) of Procion Marine HEXL at pH=3-5, after 10 min. ³¹. This oxidative treatment has advantage as it declines the chemical oxygen demand, colour and toxicity of effluent and may be utilized for the elimination of both soluble and insoluble dyes e.g. disperse dyes. The total decolourization was achieved commonly after 24 hours i.e. after the entire Fenton reagent stage. The main difficulty come across is in the separation of the solid photo catalysts at the end of the process ^{31, 32}.

Oxidation by Ozonation:

Ozone is a powerful oxidising agent and is capable of oxidising aromatic rings causing their cleavage in some textile dyes and decomposition of other organic pollutants in industrial effluents. Ozone causes the cleavage of conjugated double bonds ofchromophore in organic dyes resulting in decolorisation but this process is accompanied by the formation of toxic products. Thus ozonisation may be used along with a physical method to prevent this. Even prolonged ozonation can remove these toxic products. Ozone may react directly or indirectly with dye molecules. In the direct method, the ozone molecule acts as the electron acceptor, and hydroxide ion ( high pH) catalyse the auto decomposition of ozone to form hydroxyl free radicals (·OH) in aqueous effluents which react with organic and inorganic pollutants. At low pH ozone reacts efficiently with unsaturated chromophoric bonds of a dye molecule by direct reactions ³². The main advantage of ozone oxidation is that ozone can be applied even in its gaseous state and therefore does not cause increase in the volume of wastewater and sludge. The disadvantages of ozonation are its short halflife i.e. 20 min, its destabilisation by the presence of salts, pH, and temperature, and the added costs for the installation of ozonisation plant. The efficiency of ozonisation can be improved by using it in combination with irradiation ³³ or with a membrane filtration technique ³⁴.

Photochemical oxidation:

he UV treatment of wastewater containing dye in the presence of H₂O₂ would be able to breakdown the molecules of dye to smaller molecules, or even to final compounds of oxidation, for example, CO₂and H₂O, other inorganic oxides etc. ³⁵. The decay of dye molecules is initiated by the production of hydroxyl radicals. This procedure might be finished in a batch or continuous column unit. The productivity of this treatment relies upon the intensity of the UV radiation, pH, structure of dye and the composition of dye bath ³⁶. Hydrogen peroxide is used to raise the efficiency of photo oxidation treatment. For instance the colour elimination of more than 60-90% of Red M5B, H-acid and Blue MR dye containing effluents, has been found on working with 400-500 mg/L H₂O₂ at pH 3-7 ³⁷.

COAGULATION AND PRECIPITATION:

Coagulation:

Coagulation of dyes and other auxiliaries in textile effluents has been effectively done by Aluminum, Iron salts, Flocculants, organic polymers etc. As the coloured colloid particles from textile effluents can't be isolated by simple gravitational techniques so these are precipitated by a few chemicals, for example, lime, ferrous sulfate, ferric sulfate, ferric chloride, aluminum sulfate, aluminum chloride, cationic organic polymers, and so on which are added to settle down the ruminant colours and other effluents^38,39. These chemicals causedestabilisation of small suspended particles and emulsions mainly by neutralising their charge as a result the particles come together forming cluster of these particles large enough to settle (coagulate) under gravity or become filterable ⁴⁰. The key disadvantages of this treatment are the procedure control, impurities, for example, non-ionic cleansers staying in the effluent, and the ooze created which must be isolated and dried for later landfilling.

Electrocoagulation:

Electrocoagulation is a highly developed electrochemical treatment for the removal of color and dye. It involves processes such aselectrolytic reactions at electrodes, coagulation in aqueous effluent andadsorption of soluble pollutants on coagulants, and finally their removal by sedimentation^41,42. This treatment is efficient even at high pH for colour and COD removals and the efficiency further depends on the current density and duration of reaction. The colour removal of more than98% has been reported for textile Orange II and Acid red 14 dye-containing effluents in EC treatment⁴³. In general, decolourisation efficiency in EC treatment has been found to be 90-95%, and COD removal 30-36% under optimum conditions .The main drawback of chemical methods is the high cost which prevents it from being extensively used in industry.

BIOLOGICAL METHODS:

It involves microorganisms like fungi and Bacteria and is no cost effective to becoming popular. Biological treatment may involve degradation by combination of aerobic and anaerobic microorganisms.

Aerobic biological treatment:

This biological is the mostly used in large scale treatment of activated sludge in textileeffluent. The most important microorganisms liable for biodegradation of organic compounds are bacteria for example Aeromonas Hydrophilia,Acetobacter liquefaciens, Bacillus subtilis , Bacillus cetreus, Klebsiella pneunomoniae, Sphingomonas, Pseudomonas species, etc.; fungi for example white-rot fungi:Inonotus hispidus, Hirschioporuslarincinus, Phlebia tremellosa, Phanerochaete chrysosporium, Coriolus versicolor, etc.; algae such as Chlorella and oscillotoria species etc. Furthermore, some bacteria, white-rot fungi, mixed microbial cultures have been found to be able to degrade dyes using enzymes, such as manganese dependent peroxidases (MnP), lignin peroxidases (LiP), H₂O₂-producing enzime such as glucose-1-oxidase and glucose-2-oxidase, along with laccase, and a phenoloxidase. In biological aerated filters the organisms are grown on inert media that are held stationary during normal operation and exposed to aeration. In case of azo dyes, their nitro and sulfonic groups are quite intractable to aerobic bacterial degradation ^44,45. In any case, with azo reductases (oxygen-catalyzed chemicals), some aerobic bacteria decrease azo compounds to aryl amines ⁴⁶. Around 80% elimination of colour by degradation of azo dyes (i.e. acid Red 151; Basic Blue 41; Basic Red 46, 16; Basic Yellow 28, 19) in an aerobic bio membrane framework has been shown , which can be enhanced to more than 90% by adding activated carbon (PAC) or bentonite in aeration tank.

Anaerobic biological treatment:

Anaerobic biodegradation of water-soluble dyes such as azo dyes, has been reported to take place mainly by a redox reaction with hydrogen which result in the formation of carbon dioxide, hydrogen sulphide, methane, other gaseous compounds and release of electrons.³⁷The decolourization of the effluents is caused by the electrons released in above step which decrease the azo bonds and produce of poisonous amines⁴⁷. An extra carbon organic source, for example, glucose is vital. A chief benefit of anaerobic process notwithstanding decolourization of textile effluent is the formation of biogas, functional for heat and power production which will decrease energy costs. The primary benefit of biological treatment as compared to some physico-chemical procedures is that more than 70% of organic material expressed by COD might be changed over to biosolids The disadvantage is that the biological treatment process require long time period, hence the effluents has to be stored in large tanks for the process.

A combination of physical and biological processes has been proposed by Robinsons et. al (2001) which includes adsorption of color on agricultural waste in a constant procedure followed by color degradation utilizing solid state fermentation by micro-organisms by like white ret fungi. Here the solid waste left is non-poisonous and can be utilized as manure

CONCLUSION:

The natural and synthetic dyes which make our life colorful also cause a lot of pollution of our water bodies. Effluents from dying industry contain very harmful chemicals. The easiest way to access their impact is to study toxicity of water on aquatic plants and animals. The organic dyes should be discharged up to only certain strict limits in final effluents discharged untreated in natural water resources. Removal of Dye from textile effluents is an environmental issue which can be solved by use of adequate mechano-physic-chemical and biological treatment of textile effluents.

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Received on 12.02.2018 Modified on 26.02.2018

Asian J. Research Chem. 2018; 11(1):206-214.

DOI:10.5958/0974-4150.2018.00040.8