Laboratoire Géomatériaux et Environnement (LGE), Université Paris-Est, EA 4508, UPEM, 77454, Marne-la-Vallée, France.
School of Environmental Sciences, Mahatma Gandhi University, Kottayam, Kerala, 686560, India.
Environ Sci Pollut Res Int. 2018 Jul;25(21):20363-20373. doi: 10.1007/s11356-017-9309-6. Epub 2017 May 31.
Degradation of a widely used antibiotic, the para-aminosalicylic acid (PAS), and mineralization of its aqueous solution was investigated by electro-Fenton process using Pt/carbon-felt and boron-doped diamond (BDD)/carbon-felt cells with applied currents in the range of 50-1000 mA. This process produces the highly oxidizing species, the hydroxyl radical (OH), which is mainly responsible for the oxidative degradation of PAS. An absolute rate constant of 4.17 × 10 M s for the oxidation of PAS by OH was determined from the competition kinetics method. Degradation rate of PAS increased with current reaching an optimal value of 500 mA with complete disappearance of 0.1 mM PAS at 7 min using Pt/carbon-felt cell. The optimum degradation rate was reached at 300 mA for BDD/carbon-felt. The latter cell was found more efficient in total organic carbon (TOC) removal where a complete mineralization was achieved within 240 min. A multi-step mineralization process was observed with the formation of a number of aromatic intermediates, short-chain carboxylic acids, and inorganic ions. Eight aromatic intermediate products were identified using both LC-Q-ToF-MS and GC-MS techniques. These products were the result of hydroxylation of PAS followed by multiple additions of hydroxyl radicals to form polyhydroxylated derivatives. HPLC and GC/MS analyses demonstrated that extended oxidation of these intermediate products conducted to the formation of various short-chain carboxylic acids. Prolonged electrolysis resulted in a complete mineralization of PAS with the evolution of inorganic ions such as NO and NH. Based on the identified intermediates, carboxylic acids and inorganic ions, a plausible mineralization pathway is also deduced. The remarkably high degree of mineralization (100%) achieved by the present EF process highlights the potential application of this technique to the complete removal of salicylic acid-based pharmaceuticals from contaminated water.
采用 Pt/碳纤维和掺硼金刚石（BDD）/碳纤维两种电极的电芬顿体系，在 50-1000 mA 的电流范围内，研究了广泛使用的抗生素对氨基水杨酸（PAS）的降解及其水溶液的矿化过程。该过程产生了强氧化性的羟基自由基（OH），主要负责 PAS 的氧化降解。通过竞争动力学法确定了 OH 氧化 PAS 的绝对速率常数为 4.17×109 M s。随着电流的增加，PAS 的降解速率增加，在 Pt/碳纤维电极中，当电流为 500 mA 时，0.1 mM PAS 在 7 min 内完全消失，达到最佳降解速率。在 BDD/碳纤维电极中，最佳降解速率出现在 300 mA。后者的电极在总有机碳（TOC）去除方面更为有效，在 240 min 内可实现完全矿化。观察到多步矿化过程，形成了许多芳香族中间体、短链羧酸和无机离子。使用 LC-Q-ToF-MS 和 GC-MS 技术鉴定了 8 种芳香族中间体产物。这些产物是 PAS 羟化后多次加入羟基自由基形成多羟基化衍生物的结果。HPLC 和 GC/MS 分析表明，这些中间产物的进一步氧化导致了各种短链羧酸的形成。延长电解导致 PAS 完全矿化，无机离子如 NO 和 NH 逸出。根据鉴定出的中间体、羧酸和无机离子，还推导出了一个可能的矿化途径。本 EF 工艺实现了极高的矿化度（100%），这突出表明该技术具有从受污染的水中完全去除水杨酸类药物的潜力。
