Recent Advances in Decolorization and Degradation of Dyes in Textile Effluent by Biological Approaches PDF by Pradeep Kumar Singh, Rajat Pratap Singh, and Ram Lakhan Singh

Contents 

Preface
Synthetic dyes are widely used in textile industries. These industries generate a large volume of colored effluent which contains different types of pollutants including dyes. The release of dye-containing effluent into the environment has adverse and toxic effects on all forms of life. Therefore, removal of toxic dyes from textile effluent is necessary prior to their disposal into the environment. Different physical and chemical methods are utilized for removal of dyes from textile effluent. But these methods have several disadvantages which restrict their usage for effective treatment of textile effluent. Biological treatment methods including microorganisms and plants are efficient and eco- friendly in nature and offer several advantages over conventional physical and chemical methods. Nowadays, various advanced methods such as genetic engineering, nanotechnology, immobilized cells or enzyme, biofilms and microbial fuel cells (MFCs) are emerging as potential tools for the treatment of textile effluent. It gives us immense pleasure to introduce this Focus titled book Recent Advances in Decolorization and Degradation of Dyes in Textile Effluent by Biological Approaches. The purpose of this book is to provide updated information regarding different processes used for removal of dyes from textile effluent. This book covers all the details and aspects of textile effluent treatment. The book has been written in a simple and lucid style and is easy to follow with simple explanations and a good framework for understanding various approaches used for treatment of textile effluent. Starting with the basic knowledge of dyes and textile effluent, the book provides brief information on the toxicity of dyes and detailed discussion on various conventional and advanced methods for the treatment of textile effluent. This book will serve as a valuable resource for graduate and undergraduate students, professionals and others who are concerned with the treatment of industrial effluent.

Introduction
The population explosion combined with the industrial revolution has led to various environmental concerns. The rapid growth of industries has prompted the production of heavy loads of liquid waste. Environmental pollution, as a result of urban­ization and industrialization, has been identified as a noteworthy issue throughout the world which has a detrimental effect on human wellbeing and the biodiversity of the Earth. Food, clothing and shelter are the three fundamental needs of mankind. With the increased demand for textile products, the textile industry, and its effluents have been increasing, making them one of the prin­ciple sources of serious pollution around the world. Nature has an impressive ability of coping with small amounts of wastewater and pollution, however, it would be unsafe if the large amounts of effluent produced daily were not treated before discharging them back into the environment. The amounts and characteristics of released effluents vary from industry to industry depending on the water consumption and the average daily product. Textile indus­tries consume large volumes of potable water in various processing stages and produce vast volumes of liquid effluents containing dye (Andleeb et al. 2010; Singh et al. 2019). About 40– 65 liters of effluent is released per kilogram of fabric during the coloring process (Manu and Chaudhari 2002). Textile effluent has high biochem­ical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), total solids (TS) and also contains degradable and non- biodegradable chemicals such as dyes, dispersants and detergent, surfactants, leveling agents, heavy metal ions, dissolved inorganics, acids and alkali that are discharged into water bodies. Major pollutants and potentially hazardous compounds are discharged from the wet processing stages of textile industries.

Color is the primary contaminant to be seen in textile effluent which is mainly because of the presence of azo dyes. Azo dyes are synthetic aromatics compounds substituted with azo groups (- N=N- ). In addition to azo dyes, other classes of synthetic dyes such as anthraquinone, triphenylmethane, phthalocyanine dyes, etc. are also used in various industries. More than 100,000 dyestuffs are available commercially and annual production of the dyes is more than 7×105 tons worldwide (Selvam et al. 2003; Singh et al. 2019). These dyes are widely used in textile, paper, leather, food, cosmetic and other industries (Singh et al. 2017a). Due to inefficiency in the dyeing and finishing processes, 10– 15 percent of the total dyestuffs are discharged with the effluent into the environment (Khehra et al. 2006). These effluents can alter the physical, chemical and biological nature of the receiving water bodies such as rivers and lakes. This increase in the BOD, COD, TDS and total suspended solids (TSS), alters the pH and gives the intense colorations to water bodies. The colloidal matter present along with the colors increases the turbidity and gives the water a dirty appearance and foul smell. The release of colored textile effluent poses a serious threat to the environment. Discharge of these effluents into water streams not only creates an aesthetic problem but also these are toxic to aquatic life and eventually affect the health of both humans and animals. These colored effluents influence the transparency of water bodies and decrease the rate of photosynthesis by aquatic plants leading to damage of the aquatic environment. Moreover, some azo dyes and their deg­radation products are a serious threat to the environment due to their toxicity including mutagenicity and carcinogenicity (Wang et al. 2013). The stability and xenobiotic nature of azo dyes makes them recalcitrant. Hence it is necessary to treat the dyes present in textile effluent prior to their disposal. The treatment of polluting dyes is an important issue for small scale textile industries. These small scale industries dump their effluent into the main stream of water resources in light of the fact that their working conditions and economic status do not enable them to treat their wastewater before disposal. Without sufficient and proper treatment these dyes will remain in the environment for an extended period of time.