Removal of brilliant green tannery dye by electrocoagulation

Abstract

• Bright green dye (BG) removal from tannery wastewater by electrocoagulation (EC). • Continuous up-flow parallel plate EC reactor with 1018 steel plates as electrodes. • Decolorization and COD removal reached values up to 100% and 96%, respectively. • Best conditions were 6 mA cm −2 and 0.69 cm s −1 giving overall cost of 0.193 USD m −3 . • The removal of BG occurs by adsorption on iron oxyhydroxides flocs. This paper deals with the removal of brilliant green (BG) tannery dye from synthetically prepared water (chemical oxygen demand 660 ≤ COD ≤ 2065 mg L −1 , in 6000 mg L −1 C l - at pH 6.0) by electrocoagulation (EC) using a continuous up-flow parallel plate EC reactor. The reactor employed two 1018 steel plates as sacrificial electrodes. The influence of flocculation time (15 ≤ τ f ≤ 35 min) on the dye removal efficiency was examined, using a jar test coupled to the exit of the EC reactor. The effect of hydrodynamics, in terms of mean linear flow rate and Reynolds number (0.69 ≤ u ≤ 3.47 cm s −1 and 72 ≤ Re ≤ 362), and current density, applied to the EC reactor, and the initial BG dye concentration on the elimination of color and COD was systematically analyzed. The range of Reynolds numbers studied in the EC reactor obeys a laminar flow, Re <2100. Laminar flow pattern allows the initial floc growth to occur orderly within the EC reactor. The decolorization and COD removal reached values up to 100% and 86%, respectively, at j = 6 mA cm −2 and u = 0.69 cm s −1 ( Re = 72), giving electrolytic energy consumption and overall operating cost of 0.077 kWh m −3 (0.134 kWh (kg COD) −1 ) and of 0.193 USD m −3 (0.34 USD (kg COD) −1 ), respectively. XRD, XRF-EDS, SEM, FTIR, and OEA analysis of the dried flocs indicated the removal of BG by adsorption on iron oxyhydroxides flocs.