Electrocoagulation-flotation for orange II dye removal: Kinetics, costs, and process variables effects

The textile industry is considered a threat to water resources due to the high demand for water and the dye-rich wastewater production. Electrocoagulation-flotation (EF) is an attractive option for treating textile dyes, providing efficient color removal in a simple, reliable, and economical way. However, variables involved in the EF process need to be analyzed with the purpose of increasing removal efficiency and decreasing operating cost. Therefore, this study evaluated variables through statistical models, such as the electrode surface area, HCl concentration in the initial treatment, initial treatment time, and nitric acid volume added to the wastewater. Aluminum plates in the honeycomb configuration were used as anode and cathode. EF tests occurred with an electric current of 2.5 A, at 450 rpm of agitation for 280 min, treating 2 L of wastewater with 21 mg L-1 of orange II dye. The electrode surface (p-value = 0.0271) and the nitric acid volume (p-value = 0.0080) were the most significant variables on the dye removal efficiency. All variables and their interactions were significant (p-value <0.05) on the dye removal per surface area and aluminum electrode consumption. The reaction kinetics of dye removal indicated that the reaction order was 1.6, with an average reaction rate constant k = 0.006 +/- 0.001 mg(-0.6) L-0.6 min(-1). Therefore, the variables did not affect the removal kinetics. Daily treatment costs ranged from 4723 to 16,629 US$, demonstrating that the voltage and electrode mass consumption influence the final cost of the EF process.

Automated summary

This study evaluated key variables in electrocoagulation-flotation for treating textile dyes through statistical models, finding that the electrode surface area and nitric acid volume were the most crucial factors in dye removal efficiency. All variables had significant effects on dye removal and aluminum electrode consumption.