Electrochemical degradation of the Disperse Orange 29 dye on a β-PbO2 anode assessed by the response surface methodology

The electrochemical degradation of the Disperse Orange 29 azo dye in a filter-press flow cell using a Ti–Pt/β-PbO2 as anode was investigated by experimental design for the variables current density, pH, [NaCl], and temperature. The electrochemical system was modeled by the charge required to attain 90% decolorization (Q90) and the chemical oxygen demand removal after 120 min of electrolysis (COD120). The best conditions for Q90 were neutral to slightly alkaline solutions with low values of [NaCl] (<1.0 g L−1). On the other hand, slightly acidic to neutral conditions with higher values of [NaCl] (1.2–1.7 g L−1) yielded the highest COD120 values. These differences were ascribed to the possible formation of organochloride compounds that may lead to erroneous COD values. A total mass loss of only 0.1% was obtained during an accelerated life test of the Ti–Pt/PbO2 anode. Low levels of [Pb2+] were attained in neutral to alkaline conditions