Degradation of methyl orange by UV, O 3 and UV/O 3 systems: analysis of the degradation effects and mineralization mecha
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Degradation of methyl orange by UV, O3 and UV/O3 systems: analysis of the degradation effects and mineralization mechanism Xiang-fei Lu¨ • Hong-rui Ma • Qian Zhang • Kai Du
Received: 26 August 2012 / Accepted: 17 November 2012 Springer Science+Business Media Dordrecht 2012
Abstract The effect of ultraviolet irradiation (UV), ozonation, and the combined UV/O3 systems on the decolorization and degradation of methyl orange, performed in a laboratory-scale reactor, was studied. Decoloration efficiency, UV–vis spectrum, chemical oxygen demand (COD), mass spectrum (MS), and total organic carbon (TOC) analyses were employed. Three oxidative processes including UV, ozonation (O3), and the combined UV/O3 system were assessed to select the most appropriate oxidative process in terms of methyl orange aqueous solution treatment and special emphasis was laid on the effect of reaction pH in the UV/O3 system. The results indicated that the pH value of methyl orange solution decreased with the treatment time, and it reached an acid value when oxidized for 150 min. The COD removal efficiencies of methyl orange were only 46.23 (UV), 44.54 (O3), and 71.17 % (UV/O3) in three processes, while the corresponding decolorization efficiencies were 94.8, 94.2, and 95.1 % after 150 min of treatment. The mineralization mechanism was suggested based on the analysis of the molecular structure of methyl orange, intermediate products, and final products by using MS. For the combined UV/O3 system, the basicity condition was good at the TOC removal. Keywords Ozonation Ultraviolet irradiation Combined UV/O3 system Methyl orange
X. Lu¨ H. Ma (&) Q. Zhang K. Du Department of Environmental Engineering, College of Resource and Environment, Shaanxi University of Science and Technology, Xi’an, Shaanxi 710021, People’s Republic of China e-mail: [email protected] X. Lu¨ e-mail: [email protected]
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Introduction The textile coloration industry produces large volumes of discharge effluent, and is considered as one of the major industrial polluters in China [1]. Amongst the 10,000 different dyes and pigments available, azo dyes constitute over 50 % of all textile dyes used in the industry [2]. As an important source of environmental contamination, dye-containing wastewater has aroused more attention because most of the dyes molecules have complicated structures and they are photostable, which renders them resistant toward conventional biochemical decomposition [3]. Through new environmental concerns and regulations, pressure is being placed on textile companies to reduce pollutants and reuse process water and chemicals [4]. Methyl orange is an anionic dye, widely used in the textile, printing, paper, food colorants, cosmetic, and pharmaceutical industries. The presence of the azo group (N=N) on its molecule and low biodegradability makes it an issue of concern for environmental science [5]. The strong electron-withdrawing character of the azo group stabilizes the molecule structure and it may produce secondary waste product
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