Treatment of dinitrodiazophenol production wastewater by Fe/C and Fe/Cu internal electrolysis and the COD removal kinetics

• The difference of Fe/C and Fe/Cu IEC was discussed in DDNP wastewater treatment.
• Under the same conditions, COD removal of Fe/C IEC is greater than Fe/Cu IEC's.
• Novel pseudo-kinetics models were constructed and used to fit the COD removals.
• The COD removals are in line with the pseudo-second-order kinetic.
• The liquid film diffusion is the potential rate-controlling step.

In this study, Fe/C and Fe/Cu internal electrolysis (IE) was used to treat dinitrodiazophenol (DDNP) wastewater. COD removal was selected as evaluation index to discuss the difference of the two systems. The results of orthogonal experiment showed that under the same operational conditions, the COD removals of Fe/C IE were all greater than Fe/Cu IE, and the pH of wastewater had the greatest significant impact on COD removal. According to orthogonal and single factor affecting experiments, the optimum operational conditions of Fe/C and Fe/Cu IE were as follow: pH = 1, reaction time (RT) = 2 d, medium molar ratio (R) = 1.37 and reaction temperature (TR) = 25 °C (Fe/C IE); pH = 1, RT = 4 d, R = 1.14 and TR = 30 °C (Fe/Cu IE), and the COD removals of Fe/C and Fe/Cu IE under the optimum operational conditions were 86.65% and 82.24%, respectively. The COD removal kinetics by Fe/C and Fe/Cu IE was also investigated by classical reaction kinetics, traditional pseudo-first-order kinetic and innovative pseudo-kinetics models. The results showed that COD removal processes were well described by the novel pseudo-second-order kinetic model, and the liquid film diffusion was the potential rate-controlling step.

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