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Degradation of tyrosol by a novel electro-Fenton process using pyrite as heterogeneous source of iron catalyst

Author:
Ammar, Salah, Oturan, Mehmet A., Labiadh, Lazhar, Guersalli, Amor, Abdelhedi, Ridha, Oturan, Nihal, Brillas, Enric
Source:
Water research 2015 v.74 pp. 77-87
ISSN:
0043-1354
Subject:
4-hydroxybenzoic acid, aqueous solutions, benzoquinones, catalysts, catechol, electrodes, gas chromatography-mass spectrometry, hydrogen peroxide, hydroxyl radicals, hydroxylation, iron, mineralization, olive oil mills, oxalic acid, oxidation, pH, pyrite, reversed-phase high performance liquid chromatography, specific energy, wastewater
Abstract:
Tyrosol (TY) is one of the most abundant phenolic components of olive oil mill wastewaters. Here, the degradation of synthetic aqueous solutions of 0.30 mM TY was studied by a novel heterogeneous electro-Fenton (EF) process, so-called EF-pyrite, in which pyrite powder was the source of Fe2+ catalyst instead of a soluble iron salt used in classical EF. Experiments were performed with a cell equipped with a boron-doped diamond anode and a carbon-felt cathode, where TY and its products were destroyed by hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between Fe2+ and H2O2 generated at the cathode. Addition of 1.0 g L−1 pyrite provided an easily adjustable pH to 3.0 and an appropriate 0.20 mM Fe2+ to optimize the EF-pyrite treatment. The effect of current on mineralization rate, mineralization current efficiency and specific energy consumption was examined under comparable EF and EF-pyrite conditions. The performance of EF-pyrite was 8.6% superior at 50 mA due to self-regulation of soluble Fe2+ by pyrite. The TY decay in this process followed a pseudo-first-order kinetics. The absolute rate constant for TY hydroxylation was 3.57 × 109 M−1 s−1, as determined by the competition kinetics method. Aromatic products like 3,4-dihydroxyphenylethanol, 4-hydroxyphenylacetic acid, 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid and catechol, as well as o-benzoquinone, were identified by GC–MS and reversed-phase HPLC. Short-chain aliphatic carboxylic acids like maleic, glycolic, acetic, oxalic and formic were quantified by ion-exclusion HPLC. Oxalic acid was the major and most persistent product found. Based on detected intermediates, a plausible mineralization pathway for TY by EF-pyrite was proposed.
Agid:
5452259