Abstract
Synthetic dyes are widely used in textile, paper, food, cosmetics and pharmaceutical industries with the textile industry as the largest consumer. Among all the available synthetic dyes, azo dyes are the largest group of dyes used in textile industry. Textile dyeing and finishing processes generate a large amount of dye containing wastewater which is one of the main sources of water pollution problems worldwide. Several physico-chemical methods have been applied to the treatment of textile wastewater but these methods have many limitations due to high cost, low efficiency and secondary pollution problems. As an alternative to physico-chemical methods, biological methods comprise bacteria, fungi, yeast, algae and plants and their enzymes which received increasing interest due to their cost effectiveness and eco-friendly nature. Decolorization of azo dyes by biological processes may take place either by biosorption or biodegradation. A variety of reductive and oxidative enzymes may also be involved in the degradation of dyes. This review provides an overview of decolorization and degradation of azo dyes by biological processes and establishes the fact that these microbial and plant cells are significantly effective biological weapon against the toxic azo dyes. Int. J. Appl. Sci. Biotechnol. Vol 5(2): 108-126
Highlights
Dyes are the important industrial coloring chemical compounds
Yeast, filamentous fungi and algae has been used successfully to remove toxic dyes by biosorption (Bhatnagar and Sillanpaa, 2010). This property of microorganism is due to the cell wall components such as heteropolysaccharides and lipids, which consists of different functional groups including, amino, hydroxyl, carboxyl, phosphate and other charged groups, creating strong attractive forces between the azo dye and cell wall (Srinivasan and Viraraghavan, 2010; Das and Charumathi, 2012)
Biological processes including microorganisms such as bacteria, fungi, yeast, algae and plants overcome the limitations of physico-chemical techniques and provide an alternative approach to existing technologies for removal of azo dyes
Summary
Dyes are the important industrial coloring chemical compounds. Organic chemicals that own color are known as dyes. Oxidative enzymes Microorganisms encode number of oxidative enzymes for degradation of azo dyes such as polyphenol oxidases (PPO), manganese peroxidase (MnP), lignin peroxidase (LiP), laccase (Lac), tyrosinase (Tyr), N-demethylase (Oturkar et al, 2011; Martorell et al, 2012), dye decolorizing peroxidases (Liers et al, 2010) and cellobiose dehydrogenase (Tilli et al, 2011) These oxidases have been reported in bacteria, filamentous fungi, yeast and plants. Pure bacterial culture Bacteria mediated decolorization and degradation of azo dyes involve azoreductase assisted breakdown of azo bond (-N=N-) under anaerobic condition which results in the formation of colorless hazardous aromatic amines (Van der Zee and Villaverde, 2005) which are further removed aerobically or anaerobically (Joshi et al, 2008).
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