A Combination of Physicochemical and Biological Methods for Azo Dye Degradation

Abstract

Synthetic dyes are most commonly used in the textile, leather, paper, food, and pharmaceutical industries. Among them, textiles consume a large quantity of these dyes. The textile process uses ≤10,000 dyes with an annual production of approximately 7 × 105 t. Among the synthetic dyes, azo dyes are the largest group that is used in textile industries and are discharged as waste material, which is one of the major sources of water pollution problems worldwide. Azo dyes are mainly manufactured and used in the fabric industry. They are known as electron-deficient heterologous biological compounds and contain aromatic functional groups with ≥1 azo group (–N=N–). After treating the polluted water, these dyes are transformed from one form to another form, such as toxic compounds, secondary products, and chemical sludge in treated water. Researchers are investigating various methods to safely detoxify and discolor azo dyes in industrial wastewater. To overcome these problems, this chapter will provide a detailed review of several physical processes, such as adsorption, reverse osmosis, filtration, and irradiation and chemical methods, such as oxidation, precipitation, coagulation, and Fenton processes. In addition, various photolytic chemicals processes have been employed for the degradation of azo dyes. A review of new biological processes (e.g., the use of bacteria, fungi, algae, enzymes, and plants), which are more efficient degradation methods for azo dyes and the polluted water is less toxic, will be discussed.