Biodegradation of Azo Dyes PDF by Hatice Atacag Erkurt

Contents

Volume Preface
Synthetic dyes are extensively used in textile, dyeing, paper, printing, color photography, pharmaceutical, food, cosmetics, and other industries. Azo dyes represent about one-half of all the dyes in common use and are employed as coloring agents in the textile, food, and pharmaceutical industries. Disposal of waste water from textile industries is a problem in many parts of the world. Although these dyes are not toxic in themselves, after being released into the aquatic environment, they may be converted into potentially carcinogenic amines that impact the ecosystem and human health. The absorption of light due to textile dyes creates problems to photosynthetic aquatic plants and algae. Nowadays, the public demand for colour- free discharges to receiving water bodies has made decolourisation of a variety of industrial waste water a top priority.

Chemical and physical methods including adsorption, coagulation-flocculation, advanced oxidation and electrochemical methods are very efficient in color removal. These methods are quite expensive and have operational problems. High sludge formation, regeneration requirement and cost of adsorbent make adsorption an unattractive method for decolorization purposes. So biodegradation begins to play an important role in decolorization of azo dyes.

This volume of The Handbook of Environmental Chemistry is very important as it includes different biodegradation methods with different microorganism groups. Integration of biological processes with physical and chemical processes are also given in this volume. Several biodegradation methods can be found in this one book and it is possible to compare these methods. All the chapters in this volume have been written by authors who are experts in the field.

This book is divided into 11 chapters. The first chapter outlines the bioaugmentation of azo dyes, a process in which various microorganisms are applied to the bioreactor or the polluted sites to accelerate the desired biological processes. The second chapter focuses on the different anaerobic microbial processes of biodegradation of azo dyes and enzymes that are responsible for their degradation. The third chapter reviews the biodegradation of azo dyes in anaerobic-aerobic sequencing batch reactors, where the cyclic operations of SBR provide both color removal in the anaerobic stage and aromatic amine removal in the aerobic stage. The fourth chapter outlines azo dye degradation by immobilized bacteria and concludes that immobilization increases the stability of the enzyme at high pH and tolerance to elevated temperatures and makes the enzyme less vulnerable to inhibitors. The fifth chapter focuses on bacterial decolorization and degradation of azo dyes catalyzed by redox mediators and the further investigation to enhance the applicability of redox mediators to the bio-transformation of azo dyes. In the sixth chapter, a survey of the state-of-the-art of azo-dye conversion by means of bacteria is presented with a focus on reactor design and operational issues. The relevance of thorough characterization of reaction kinetics and yields is discussed. The second section focuses on recent results regarding the conversion of an azo-dye by means of bacterial biofilm in an internal loop airlift reactor. Experimental results are analyzed in the light of a comprehensive reactor model. The seventh chapter outlines the treatment of azo dye-containing waste water using integrated processes like combined physical biological processes and combined chemical biological processes. The eighth chapter is about the role of white rot fungi in biodegradation of azo dyes and the detection of enzymes responsible for azo dye decolorization. The ninth chapter is about decolorization of azo dyes by immobilized fungi. The tenth chapter focuses on decolorization of azo dyes with another fungus group: yeasts. The last chapter highlights the factors affecting the complete mineralization of azo dyes.