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Phenol and cresols treatment in aqueous solution by electro-Fenton process: Application to the mineralization of aeronautic wastewater industry

Abstract : Oxidation of phenol and cresols in aqueous media by electro-Fenton process using carbon felt cathode has been studied. The absolute rate constant of phenol and o-cresol degradation by hydroxyl radicals were obtained in acid medium (2.5 < pH < 3.0), being respectively equal to (2.62  0.23) x 109 M-1 s-1 and (3.70  0.19) x 109 M-1 s-1. The salts of iron, cobalt, manganese and copper were used to provide the metal cations as catalyst of Fenton reaction to produce hydroxyl radicals. 10-4 M of soluble iron(II) sulfate salt supplied the optimum catalytic condition, allowing to remove 100% of total organic carbon (TOC) of aqueous phenol solutions. The main reaction intermediates (environ 70%) formed during phenol electro-Fenton treatment were identified as hydroquinone, p-benzoquinone and catechol. Carboxylic acids such as maleic, fumaric, succinic, glyoxylic, oxalic and formic were predominantly identified as end products, before complete mineralization. During o-cresol electrolysis, the main initial reactions (about 58%) were successively electrophilic additions of hydroxyl radical on the aromatic ring, leading to the formation of 3-methylcatechol and methyl-hydroquinone. Fumaric and succinic acids were predominantly formed in initial stages, but there were also traces of piruvic and maleic. Oxalic, acetic and glyoxylic acids were predominant formed in final stages. Experiments with electro-Fenton oxidation of most identified intermediates allowed to propose a complete mineralization pathway to phenol and o-cresol. The predominant acids produced in first stages of m-cresol degradation by electro-Fenton process were glycolic, succinic, malonic and piruvic acids. These acids were rapidly converted in glyoxilic, acetic, oxalic and formic. After 450 minutes, high concentrations of acetic and oxalic acids showed greater persistency to total mineralization. The main identified acids in first stages of p-cresol degradation were glicolic, malonic, piruvic and formic acids. After 125 minutes, acetic acid was predominant, being completely degraded after 550 minutes. During real effluent treatment, the replacement of Pt anode by BDD, under the same experimental conditions, increased significantly the efficiency of electro-Fenton process, removing about 98% of TOC in 20 hours of reaction. The presence of chrome did not harm the efficiency of the process. High mineralization rates evidenced the efficiency of the electro-Fenton as an advanced oxidation process to treat stripping aircraft wastewater.
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Marcio Pimentel. Phenol and cresols treatment in aqueous solution by electro-Fenton process: Application to the mineralization of aeronautic wastewater industry. Environmental Engineering. Université Paris-Est; Universidade Federal de Rio de Janeiro, 2008. English. ⟨tel-00742470v1⟩

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