Microwave-enhanced UV/H₂O₂ degradation of an azo dye (tartrazine): optimization, colour removal, mineralization and ecotoxicity

Abstract

This study optimizes two factors, pH and initial [H₂O₂], in the ultraviolet (UV)/H₂O₂/microwave (MW) process through experimental design and assesses the effect of MWs on the colour removal of an azo-dye (tartrazine) solution that was favoured by an acidic pH. The estimated optimal conditions were: initial [H₂O₂]=2.0 mmol L⁻¹ and pH=2.6, at 30±2°C. We obtained colour removals of approximately 92% in 24 min of irradiation (EDL, 244.2 W), following zero order kinetics: k=(3.9±0.52)×10⁻² a.u. min⁻¹ and R ²=0.989. Chemical and biological oxygen demand were significantly removed. On the other hand, the carbon content, biodegradability and ecotoxicity (Lactuca sativa) remained approximately the same. The UV/H₂O₂/MW process was shown to be eight times faster than other tested processes (MW, H₂O₂, H₂O₂/MW, and UV/MW).

Keywords:

• advanced oxidation processes
• AOPs
• microwave
• UV/H₂O₂
• tartrazine
• electrode-less discharge lamps
• EDLs

Acknowledgements

The authors appreciate the generous financial support of this work by The National Council for Scientific and Technological Development (CNPq), Brazil.