Removal of organic dyes and tannins by electrochemical techniques

Abstract

Removal of organic dyes, tannins and phenol based molecules from aqueous solutions and the amenability of electrochemical techniques for the treatment of dye bath and tannery effluents was discussed. In the case of electro-coagulation/flotation, aluminum and steel were used as electrodes whereas graphite and IrO2/TaO2/RuO2 coated Ti electrodes were tried for electro-oxidation. The degradation of dyes such as CI Reactive blue 221 and CI Acid orange 10, phenol based tannins and phenolics such as resorcinol, pyrogallol, catechol and phloroglucinol was studied both by electrocoagulation and electro-oxidation techniques. The decolourization and degradation of the dye molecules was monitored by UV-visible spectrophotometer and the mineralization trend of all these compounds was followed by chemical oxygen demand (COD) and total organic carbon (TOC) measurements. The effect of operating parameters such as nature of the electrolyte, pH, and applied current density were discussed. The generation of chlorine based in situ oxidants has been confirmed by cyclic voltammetric technique. Electro-oxidation of the dyes and tannin molecules was evaluated and found that the graphite material was effective to achieve the complete mineralization. Although, IrO2/TaO2/RuO2 coated Ti anode is chemically inert and structurally stable, it fails to generate more molecular oxygen and hydroxyl radicals. The purification of textile and tannery effluent was successfully achieved by electrochemical treatment processes.