Electrochemical coagulation for textile effluent decolorization

Abstract

The three most commonly used dyestuffs in textile industry are reactive, acid, and dispersed dyes. One dye from each group, C.I. Reactive Blue-19, C.I. Acid Red-266, and C.I. Disperse Yellow-218 was chosen to study the feasibility of coagulation for color removal. The dyes used in these experiments were chosen to represent the two major structural features: anthraquinone and azo dyes. Reactive Blue is an anthraquinone-based dye, and Acid Red and Disperse Yellow represent azo-based dyes. As there is no standard method to measure the color intensity, a Hach spectrophotometer was used to measure the absorbance before and after the dye solution was treated. Removal efficiencies on these dyes were obtained by measuring absorbance of a sample at 592 nm for Reactive Blue, 498 nm for Acid Red, and 428 nm for Disperse Yellow. Aluminum and ferric coagulants were produced in a parallel-plate electrochemical reactor by anodic dissolution. Removal efficiencies of more than 98%, in terms of absorbance, were observed in laboratory conditions. Removal was found highly dependent upon NaCl concentration, applied voltage, current density, and pH. The NaCl in the solution effectively reduced the power consumption and promoted the coagulant generation by depasivating the Al-water and Fe-water electrochemical systems. The processes were determined to be highly NaCl dependent. A mechanism was proposed for the corresponding liquid phase chemistry.