Enhancement of decolorization rate and COD removal from dyes containing wastewater by the addition of hydrogen peroxide under solar photocatalytic oxidation

The solar photocatalytic decolorization and degradation of Maxoline Navy 2 RM 200% basic dye in aqueous solution with TiO2-A (pure anatase) as photocatalyst in slurry form have been investigated using solar light. The removal of the dye was strongly enhanced by the addition of electron acceptors such as hydrogen peroxide (H2O2). The effects of various parameters such as amount of hydrogen peroxide, initial dye concentration, catalyst loading, pH-values on decolorization rate have been determined. The semi-logarithmic plots of absorbance data gave a straight line. The correlation constants for the fitted lines were calculated to be ranged from r = 0.97 to 0.99. This finding indicates that the solar photocatalytic decolorization of the dye in aqueous TiO2 suspensions can be described by the pseudo first-order kinetic model. The optimum operating conditions were to be: 1 g/L TiO2, 1.5 ml/L H2O2, pH=3–5. The effect of dye-assisting chemicals such as Na2CO3 and NaCl has been also investigated. Addition of these chemicals inhibits the removal rate. At optimum operating conditions, color removal from the effluent reached 99.9% after 90 min irradiation time. Measuring of total organic carbon (TOC) loss showed that the dye was mineralized by 60% within this time and 75% within 240 min irradiation time under these conditions indicating that the dye is also efficiently degraded. Nevertheless, the persistence of a low level of TOC indicated that mineralization was not complete and dead-end product(s) which was (were) resistant to solar photocatalytic oxidation might have accumulated.