Treatment of dye-containing effluent by natural clay

• Effluents containing anionic dyes are discolored by raw clay.
• Chemicals added in the dyeing process enhance adsorption of dye onto clay.
• Enzymatic additives help dye adsorption contrary to cationic additives.
• High ionic strength and pH enhance adsorption of anionic dye onto clay.

Treatment of dye-containing effluents is a significant challenge because dyes are toxic and pose a threat to the environment. Recent studies have shown that natural clay is able to efficiently remove colour from effluents that contain dyes and various additives. The objective of this study is to investigate the combined effects of dyes, salts and auxiliary chemicals used in the dyeing process, on the adsorption process onto natural clay for the treatment of dye-containing effluents. Batch adsorption experiments were performed using real and synthetic effluents containing dyes (Reactive Red 120, Reactive Orange 84 and Reactive Blue 160), and natural clays (Fouchana and Tabarka). The results show that both of the natural clays are efficient in treating real effluents. Fouchana clay shows a higher efficiency than Tabarka clay in the discolouration of the most colour loaded solution. The added chemical of enzymatic nature (Catalase) facilitates the adsorption of anionic dyes onto clay, likely by electrostatic attraction interaction with the SO3- groups in the dye, followed by the adsorption onto the clays, of the dye-enzyme system. The mixture of all additives, enhances the adsorption of dyes on the clays, and does not act as a barrier to the decolouration process. Therefore, clays which are inexpensive and effective adsorbents may be promising alternatives for the treatment of the textile dyeing effluents.

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