Electrochemical oxidation of bio-refractory dye in a simulated textile industry effluent using DSA electrodes in a filter-press type FM01-LC reactor

Abstract

This work presents a study on degradation of indigo carmine dye in a filter-press type FM01-LC reactor using Sb₂O₅-doped Ti/IrO₂-SnO₂ dimensionally stable anode (DSA) electrodes. Micro- and macroelectrolysis studies were carried out using solutions of 0.8 mM indigo carmine in 0.05 M NaCl, which resemble blue denim laundry industrial wastewater. Microelectrolysis results show the behaviour of DSA electrodes in comparison with the behaviour of boron-doped diamond (BDD) electrodes. In general, dye degradation reactions are carried out indirectly through active chlorine generated on DSA, whereas in the case of BDD electrodes more oxidizing species are formed, mainly OH radicals, on the electrode surface. The well-characterized geometry, flow pattern and mass transport of the FM01-LC reactor used in macroelectrolysis experiments allowed the evaluation of the effect of hydrodynamic conditions on the chlorine-mediated degradation rate. Four values of Reynolds number (Re) (93, 371, 464 and 557) at four current densities (50, 100, 150 and 200 A/m²) were tested. The results show that the degradation rate is independent of Re at low current density (50 A/m²) but becomes dependent on the Re at high current density (200 A/m²). This behaviour shows the central role of mass transport and the reactor parameters and design. The low energy consumption (2.02 and 9.04 kWh/m³ for complete discolouration and chemical oxygen demand elimination at 50 A/m², respectively) and the low cost of DSA electrodes compared to BDD make DSA electrodes promising for practical application in treating industrial textile effluents. In the present study, chlorinated organic compounds were not detected.

Keywords:

• DSA electrodes
• active chlorine
• indigo carmine
• electrochemical oxidation
• FM01-LC

Acknowledgements

F.A. Rodriguez (grant holder number 227108) is grateful to CONACyT for the grant for her postgraduate studies. The authors thank the Research and Technology Innovation Project Support Program (PAPIIT for its initials in Spanish) of the Universidad Nacional Autónoma de México (UNAM) for the financial aid given through the project no. 224711. SEM-EDS images were taken by Prospero Acevedo-Peña at Laboratorio Central de Microscopía Electrónica, UAM-Iztapalapa.