Effect of dye molecules and electrode material on the settling behavior of flocs in an electrocoagulation induced settling tank reactor (EISTR)

A simple electrocoagulation induced settling tank reactor (EISTR) was fabricated to study the dye removal and sedimentation kinetics of Amido Black 10B (AB), Methyl Violet (MV), Eosin Yellow (EY), Malachite Green (MG), Methylene Blue (MB), Rhodamine 6G (R6G), their binary, tertiary mixtures and actual textile effluent. Optimum conditions such as current density, electrolysis time, initial pH and NaCl concentration to achieve high color removal efficiency (CRE) and sludge settling velocity were evaluated for the removal of 100 mg/L AB dye. The CRE and chemical oxygen demand (COD) reduction, initial sludge settling velocity, final sludge height and turbidity reduction were measured. These experiments indicate that 81-99% CRE, 54-68% COD reduction and 73-88% turbidity reduction can be achieved for the synthetic as well as textile dye wastewater systems. Around 3.8 Ah of charge loading per gram of dye was found to be sufficient for high CRE and satisfactory sedimentation kinetics for most of the dyes. The energy requirement was found to be 24 ± 3 Wh g^-1 of dye molecule. Fe electrodes perform better when compared to Al electrode in similar operating conditions. XRD and SEM studies indicate that relatively large porous low density aluminum hydroxide flocs formed under the induced sedimentation conditions do not settle effectively. Relatively smaller and denser iron hydroxide flocs generated using Fe electrode leads to relatively better performance.