**2.1 Textile industry effluents: Composition and conventional methods of treatment**

Textile industry effluents contain large quantities of biodegradable organic compounds and nonbiodegradable compounds [14]. According to the literature, there are more than 8000 substances, such as acids, surfactants, salts, metals, oxidizing agents, reducing agents, as well as dyes and their auxiliaries [15]. Wastewater from the textile industry contains characteristic color, resulting from the mixture of dyes, in addition to the presence of metals, organic carbon, ammonium salts, nitrate, and orthophosphate [5].

Due to the environmental impact of this type of effluent, pretreatment is necessary before such compounds are released into natural water bodies, and the textile industry shows interest in controlling this problem [14]. However, even after treatment, effluents are still discarded in rivers with up to 90% of dyes that have not undergone chemical changes [1]. **Table 2** shows information related to the studied treatment processes for the removal of textile dyes from industrial effluents and the main results obtained, as reported in the literature.

The composition, as well as the standards allowed for each substance present in the composition of effluents from textile factories, aiming at its release in surface water bodies, vary according to the standards of each country. In China, the chemical oxygen demand (COD) and chrominance of wastewater from dyeing and finishing processes cannot exceed 80 mg L−1 and 60, respectively, so that such effluents can be

