Background and Aims: Dyes are widely used in different industries and consequently are disposed through different industrial effluents into the environment. Chronic and/or acute effects of the chemicals on microorganisms have been documented. Dyes may absorb and reflect the entering sun lights into the water and thereby decrease the algal photosynthesis. The later in turn can affect the food chain seriously. The aim of this study was, therefore, to use MgO nanoparticles as catalyst in heterogenic catalytic ozonation process (COP) for reactive red 120 dye removal (decolorization) from synthetic wastewater.Materials and Methods: MgO nanoparticles were produced by sol-gel method. The influences of several operational parameters including solution pH, reaction time, MgO dosage and initial dye concentration on removal (decolorization) efficiency were evaluated.Results: The optimum pH and MgO dosage for COP were determined as 10 and 3 g/L, respectively. Decolorization of 500 mg/L of dye was almost complete after 12 min under achieved optimum conditions. MgO nanocrystals markedly affected the COP and enhanced the dye removal efficiency by approximately 49% compared with the sole ozonation process.Conclusion: Higher O3 decomposition in presence a small amounts of catalyst and alkaline pH increases the radical production which in turn improves the decolorization efficiency. Increasing the initial concentration of dye deteriorated the removal efficiency; however, this can be compensated by increasing the ozonation rate.Key words: Catalytic Ozonation, MgO Nanoparticles, Reactive Red 120 dye (RR120)
