A Review Biotechnological removal of color and dye from waste water
Alpesh J.Shiroya*, K.K.Vaghasiya, N.J.ghantala
Bhagwan Mahavir College Of Biotechnology ,
Clean technology has become an important concern for every industry. Especially in textile dyeing factories, there is much use of water, energy, dyeing colours and chemicals. This can cause significant water and air pollution problems. The wastewater wear a lot of colour and having toxic odour, COD and BOD. wastewater contains the following reactive dyes: turquoise DG, black DN, red DB-8 and orange OGR. It has been shown that the efficiency of dye removal depends on the type of dye, coagulant dosage, and the sample pH.The performance of COD and colour removal in the single-stage ozonation- biological treatment was also compared with the multi-stage ozonation-biological treatment processes. Ozonation transforms the functional groups in azo dye to produce more biodegradable by products, which is easily removed by biological treatment. semiconductor photocatalysis process could be an appropriate tool for the treatment for textile dyeing and printing wastewater. Activated sludge treatment and the coagulation-flocculation method with ≥80% removal efficiency of waste water. Using the electrocoagulation process possible the reuse of dye wastewater by removing the colours. sequential batch reactor (SBR) technology as an alternative method for treating industrial effluents.In the present work we review existing processes as well as promising new technologies for texttile waste water decolorisation.
Reference Id: PHARMATUTOR-ART-1368
[ I ] INTRODUCTION
Water is life but now a-days due to the advancement in industrialization, it is spoiling a lot. Many contaminants present in wastewater, such as acids, bases, toxic organic and inorganic dissolved solids, and colors. Among them, colors are considered the most undesirable and are mainly caused by dyes . Presence of colour and its causative compounds has always been undesirable in water used for either industrial or domestic needs. Different colouring agents like dyes, inorganic pigments, tannins, lignins etch usually impart colour. Amongst complex industrial wastewater with various types of colouring agents, dye wastes are predominant . This wastewater not only toxic to the biological world, but it also has a dark colour, which blocks sun light. By these reasons, it causes many problems to the ecosystem . The number of dyes presently used in textile industry is about 10,000. Among these dyes, azo dyes constitute the largest and the most important class of commercial dyes. Azo dyes are widely used in textile, plastic, leather, and paper industries as additives . The removal of azo dyes in aquatic environment is important because many azo dyes are toxic to aquatic organisms .
There are some methods used for the treatment of dye-containing wastewater . Coagulation is effective for treatment of insoluble dyestuff wastewater but not so effective for soluble dyestuff wastewater [7, 8]. The adsorption method has difficulties in the treatment of insoluble dyestuff wastewater and it is very difficult to find the desorption process [8,9]. The chemical method is to oxidize organic materials by oxidizing agents, such as ozone, H2O2, UV light or combination of such oxidants that is known as Advanced Oxidation Processes (AOPs). Most factories use this method to reduce COD and colour. But, it cannot satisfy the environmental discharge standard by itself alone and the cost is relatively high. The combination of ozonation and biological treatment seems to be promising unit processes to remove residual colour, COD and BOD of wastewater containing dye. The reaction between the oxidizing agent with dye in an aqueous environment lead to the decrease in aromaticity and molecular weight which eventually result in an increase in biodegradability and colour removal of dye. The biodegradable compound produced during ozonation would be removed by the following biological treatment. Therefore, the improvement of biodegradability is considered to be essential factor that determines the performance of ozonation –biological treatment process.
Dye: Technologies for Colour Removal
Over the last few decades, society has become increasingly sensitive towards the protection of the environment. Due to this problem, mankind nowadays has concern about the potential adverse effects to the chemical industry on the environment, although the response in some parts of the world has been much faster and more intense than in others. The colour manufacturing industry represents a relatively small part of the overall chemical industry. Dyes and pigments are highly visible material. Thus even minor release into the environment may cause the appearance of colour, for example in open waters, which attracts the critical attention of public and local authorities.
Dyes are widely used in the Textile, rubber product, paper, printing, color photography, Pharmaceuticals, Cosmetics and Many other industries . Dyes usually have a synthetic origin and complex aromatic molecular structures which make them more stable and more difficult to biodegrade . Dyes tinctorial value is high: less than 1 ppm of the dye produces obvious coloration . Due to their chemical structure, dyes are resistant to fading on exposure to light, water, and many chemicals . Due to their complex struc-ture and synthetic origin, many dyes are difficult to be decolorized and decomposed biologically. There are many structure varieties such as acidic, basic, disperse, azo, diazo, anthroquinone based, and metal complex dyes.
[ II ] TECHNOLOGIES FOR COLOR REMOVAL
There are more than 100,000 commercially available dye exist and more than 7x105 tonnes per year are produced annually [14,15]. Wastewater containing dyes is very difficult to treat, since the dyes are recalcitrant organic molecules, resistant to aerobic digestion, and are stable to light. A synthetic dye in wastewater cannot be efficiently decolorized by traditional methods. This is because of the high cost and disposal problems for treating dye wastewater at large scale in the textile and paper industries . The technologies for colour removal can be divided into three categories: biological, chemical and physical . All of them have advantages and drawbacks.
A. Biological methods
Biological treatment is the often the most economical alternatives when compared with other physical and chemical processes. Biodegradation methods such as fungal decolourization, microbial degradation, adsorption by (living or dead) microbial biomass and bioremediation systems are commonly applied to the treatment of industrial effluents because many microorganisms such as bacteria, yeasts, alges and fungi are able to accumulate and degrade different pollutants [15,17]. However, their application is often restricted because of technical constraint. According to Bhattacharyya and Sharma, (2003),  biological treatment requires a large land area and is constrained by sensitivity toward diurnal variation as well as toxicity of some chemicals, and less flexibility in design and operation. Further, biological treatment is incapable of obtaining satisfactory colour elimination with current conventional biodegradation processes .
There are many types of biological treatment methods. Among them include trickling filters, activated sludge process, anaerobic process, oxidation ponding etc. To date the commonest treatment of textile wastewater has been based on mainly on aerobic biological process, consisting mainly conventional and extended activated sludge system. The trickling filters simulate stream flow by spraying wastewater over a broken, medium such as stone or plastic. The medium serves as a base for biological growth, which attacks the organic matter of wastewater, and uses it as food.
In activated sludge process, the wastewater flows into a tank after primary settling. The microorganism in activated sludge is suspended in the wastewater as aggregates. The sludge and wastewater is kept in suspension by compressed air, which also supplies the oxygen, necessary for biological activities. The aerated waste is continuously withdrawn and settled and a portion of the sludge is returned to the influent.
Biological methods of removing pollutants from wastewater using natural process involving bacteria and other microorganism for oxidation of the organic waste. Biological methods are generally cheap and simple to apply and are currently used to remove organic and color from dyeing and textile wastewater. Most of existing process includes an initial step of activated sludge treatment to remove the organic matters, followed by oxidation, membrane, activated carbon etc.
Anaerobic and aerobic treatments have been used together or separately for the treatment of textile effluents. Hence aerobic treatment is not effective in colour removal from textile wastewater containing azo dyes. Conventional biological process are not effective for treating dyestuff wastewater because many commercial dyestuff are toxic to organism being used and result in the problems of sludge bulking, rising sludge and pin flock. Because of low biodegradability of many textiles chemicals and dyes, biological treatment is not always effective for textile industry wastewater .
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