Green chemistry for dyes removal from waste water

Dyes are used in large quantities in various industries including textiles, healthcare, paint, printing, leather processing and food processing, etc. to colour their products. Only a small fraction (10–20%) of a dye is actually used in the process and rest of the dye ends up in wastewater generated by dye-using industries. Disposal of dye laden wastewater imparts colour to the receiving water bodies. Colour impedes light penetration, photosynthetic activity, inhibits the growth of biota and interferes with the projected use of water bodies. Contamination of potable water by dyes even at very low concentrations could make it unfit for human consumption. This issue needs to be addressed seriously. Several technologies are available for dyes removal from wastewater but each method has its advantages and limitations. Thus, the scientific community is searching for new, non-polluting and sustainable processes which can be effectively employed for dyes removal from wastewater.

This book, entitled Green chemistry for dyes removal from waste water (edited by Sanjay K. Sharma), contains 11 chapters dealing with different aspects of dyes removal from wastewater including physical, chemical, biological and integrative approaches.

In the first chapter, the authors present the classification of dyes and various technologies available for colour removal from wastewater. Various physical methods used for dye removal including adsorption, membrane filtration, ion exchange, irradiation and electrokinetic coagulation are described in detail. In addition to this a brief account of aerobic and anaerobic degradation of dyes has also been integrated into the chapter.

Chapter 2 is focused on the use of nanoadsorbents for the removal of dyes from textile dye-laden water. In recent years a good volume of data has been published on the use of carbon nanotubes and grapheme for dye removal from water and wastewater. In this chapter the authors present a comprehensive update of the use of carbon-based nanoadsorbents for the removal of dye from wastewater along with their advantages and limitations in this field.

Advanced oxidation processes (AOPs) have emerged as a powerful technology to treat dyes-containing wastewaters. These processes are based on the production of highly reactive radicals which promote the destruction of the target pollutant. In chapter 3, the authors describe various AOPs including ozonation, Fenton’s reagent oxidation, wet air oxidation and phytocatalytic oxidation for the removal of dyes from an aqueous medium.

Heterogeneous photocatalysis has huge potential in tertiary treatment of wastewater. In chapter 4, the authors present the basic theory and mechanism of photo-oxidation processes followed by the application of solar light in dye degradation. This chapter also deals with design features, efficiencies and process parameters of solar photoreactors.

Adsorption or biosorption has proved to be one of the most promising and efficient dye removal techniques from industrial wastewater. But due to the high cost of the commercially available activated carbon the scientific community is continuously searching for effective but economically cheaper adsorbents. The importance of this field is evident by the fact that five chapters of the book are devoted to removal of dyes from wastewater employing adsorption.

In chapter 5, the authors review dye removal from wastewater using biowaste-derived adsorbents. The authors review various studies conducted in previous years for dye removal from wastewater using rice husk, bagasse, peat, bamboo, date pits, palm tree waste, coconut waste and tea and coffee waste. The effect of chemical modification of biowastes on dye removal has been compiled in tabular forms which enhances the value of the chapter.

In chapter 8, some important aspects of biosorption including classification, advantages, properties of biosorbents and process parameters which may affect the efficiency of the process are reviewed.

In chapter 9, the authors review the use of natural and modified clays, viz., bentonite, montmorillonite and vermiculite for the removal of cationic as well as anionic dyes.

In chapter 10, the authors focus on non-conventional biosorbents for dye removal from wastewater. In this chapter an exhaustive list of non-conventional adsorbents has been compiled and the results in terms of adsorption capacity are discussed.

In chapter 11, the authors present an elaborative discussion of the removal of two azo dyes, viz., tartazine and amaranth, using hen feathers as an adsorbent. This chapter includes the results of various experiments undertaken by the authors.

Use of ligninolytic enzymes for the degradation of synthetic dyes is a relatively new emerging technology. This process employs a hybrid of chemical and biological oxidation using a combination of crude or purified enzymes as biocatalysts or chemical oxidants. In chapter 6, the authors discuss the sources and application of fungal laccases and peroxidise enzymes for the treatment of synthetic dyes, reaction mechanisms and other development and challenges associated with enzymatic processes.

Ultrasound has emerged as a sustainable option via generating reactive oxidising and reducing species which are capable of degrading dyes in wastewater. In chapter 7, the authors give an overview of textile dyeing mill wastewater and its treatability by ultrasonic irradiation and hybrid processes which utilises ultrasound focusing on the degradation and mineralisation of reactive azo dyes.

In conclusion, the authors have been successful in providing a holistic account of various green technologies which have immense potential in dye removal from wastewater. Furthermore all the information is well documented with a good number of references by which readers can further deepen their knowledge on these aspects. This book can be a platform for the researchers working in the field of green processes for important techniques such as biosorption, advanced oxidation processes, photocatalytic processes, nanotechnology, etc. Therefore, I recommend the book for postgraduate students, PhD scholars and researchers working in the concerned research areas.