Comparative study on treatment of methylene blue dye wastewater by different internal electrolysis systems and COD removal kinetics, thermodynamics and mechanism

Abstract

In this study, Fe/Cu, Fe/Al/Cu, Fe/Cu/C and Fe/Al/Cu/C internal electrolysis systems (IESs) were constructed and used to treat methylene blue dye (MB) wastewater. The effects of filler mass ratio, filler dosage, solution pH, reaction time and reaction temperature on COD removal were discussed, while the kinetics, thermodynamics and mechanism of COD removal were also investigated. The results showed that when the COD removal rates were basically the same, the reaction times of Fe/Al/Cu, Fe/Cu/C and Fe/Al/Cu/C IESs were shorter, and the filler dosages were lower. For the four systems, the appropriate pH was around 5, while the suitable reaction temperature was in the range of 20-25 °C. The COD removals of these four IESs were generally greater than 90%. The COD removal processes of the four systems could be better described by the improved pseudo-second-kinetic model, and the liquid film diffusion was the rate-controlling step. Moreover, the COD removal was a spontaneous and endothermic process. MB was degraded into inorganic substances in four steps. In addition, the FTIR characterization of the fillers before and after reaction suggests the four IESs have good stability.

Keywords: Internal electrolysis systems; Kinetics; Mechanism; Methylene blue dye wastewater; Thermodynamics.