International Journal of Membrane Science and Technology, 2023, Vol. 10, No. 2, pp 3738-3744 3738 Decolorization by Catalytic Ozonation USING Mn(II) Fe(II) and Fe(III) Watcharapol Wonglertarak 1 , Boonchai Wichitsathian 2* , Jareeya Yimrattanabavorn 3 1 Environmental Engineering and Disaster Management Program, Mahidol University, Kanchanaburi campus, Kanchanaburi, Thailand. 2 School of Environmental Engineering, Institute of Engineering, Suranaree University of Technology, Nakhon Ratchasima, Thailand. boonchai@sut.ac.th 3 School of Environmental Engineering, Institute of Engineering, Suranaree University of Technology, Nakhon Ratchasima, Thailand. Abstract: The textile industry holds significant importance in Thailand. It has been estimated that 10-20% of dyes are lost during the dyeing process and subsequently released into wastewater. The high concentration of non- biodegradable substances in these wastewaters makes them challenging to treat using conventional methods. Therefore, this study aimed to assess the effectiveness of a catalytic ozonation process employing Mn(II), Fe(II), and Fe(III) for treating synthetic dye wastewater. The study also sought to optimize operational parameters such as pH and contact time. Both with and without catalytic ozonation, experiments were conducted in a batch reactor with a consistent ozone flow rate of 6 g/hr. Under the non-catalytic ozonation conditions, it was observed that more than 90% of decolorization occurred within 15 minutes at a pH of 9. The ozonation of the dye followed a first-order reaction mechanism at room temperature, with a rate constant (k) of 0.18 min -1 . The catalytic ozonation used a concentration of 1.2 mM of Mn(II) was showed color removal of 90% in 8 min. For catalytic ozonation used Fe(II) and Fe(III) with concentrations of 0.6 mM showed color removal of 90% in 10 min. The highest rate constant (k) showed 0.29 min -1 for Mn(II) and 0.21 min -1 for Fe(II) and Fe(III). In conclusion, the study found that the inclusion of a catalyst substantially enhanced the degradation efficiency of the dye compared to ozonation without a catalyst. Keywords: Decolorization, Dye Wastewater, Catalytic Ozonation, Advance Oxidation Process. 1. INTRODUCTION The textile industry has played a vital role in Thailand's economic development over the past few decades. In this sector, approximately 200,000 tons of dyes are utilized. These dyes, classified as water-soluble, exhibit a loss of 10- 20% during the dyeing process, ultimately released into wastewater [1]. Textile wastewater is characterized by a significant presence of refractory organic substances and color, which consist of toxic and non-biodegradable compounds [2]. Conventional technologies face challenges in effectively treating these complex wastewaters [3]. Advanced Oxidation Processes (AOPs) represent a category of chemical treatment methodologies designed for eliminating organic compounds from water and wastewater. These techniques operate by generating hydroxyl radicals, which are highly effective in purifying water. AOPs encompass various methods, including ozonation, photocatalytic degradation, the use of Fenton's reagent (comprising H2O2/Fe 2+ ), Electro-Fenton, photo-Fenton processes, UV/chlorine treatment, and wet air oxidation. Importantly, these methods are particularly efficient in degrading organic pollutants under pressure conditions and ambient temperature. Ozone and ozone-based advanced oxidation systems are acknowledged as potent and environmentally friendly technologies capable of efficiently degrading a broad spectrum of organic pollutants [4]. In recent years, the application of ozonation in wastewater treatment has experienced substantial growth. Significantly, ozonation stands out as the preferred technique for removing colored substances characterized by chromophore groups with conjugated double bonds. These compounds can be effectively disintegrated into smaller molecules through both