Degradation of trans-ferulic acid in acidic aqueous medium by anodic oxidation, electro-Fenton and photoelectro-Fenton

• Published in: Journal of hazardous materials 2016-12, Vol.319, p.3-12
• Main Authors: Flores, Nelly, Sirés, Ignasi, Garrido, José Antonio, Centellas, Francesc, Rodríguez, Rosa María, Cabot, Pere Lluís, Brillas, Enric
• Format: Article
• Language: English
• Subjects: Anodic oxidation; Anodizing; Carbon; Current density; Degradation; Electro-Fenton; Mills; Mineralization; Olea; Oxidation products; Photoelectro-Fenton; Substrates; trans-Ferulic acid; Wastewater treatment
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2015.11.040

•trans-Ferulic acid degradation by EAOPs using a stirred BDD/air-diffusion cell.•Slow substrate abatement and poor mineralization by AO-H2O2.•98% Mineralization by PEF, but with rapid and similar substrate decay than by EF.•Quicker degradation by SPEF due to the more potent photolytic action of sunlight.•Reaction pathway with four primary aromatic products and three final carboxylic acids. Solutions of pH 3.0 containing trans-ferulic acid, a phenolic compound in olive oil mill wastewater, have been comparatively degraded by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). Trials were performed with a BDD/air-diffusion cell, where oxidizing OH was produced from water discharge at the BDD anode and/or in the solution bulk from Fenton’s reaction between cathodically generated H2O2 and added catalytic Fe2+. The substrate was very slowly removed by AO-H2O2, whereas it was very rapidly abated by EF and PEF, at similar rate in both cases, due to its fast reaction with OH in the bulk. The AO-H2O2 process yielded a slightly lower mineralization than EF, which promoted the accumulation of barely oxidizable products like Fe(III) complexes. In contrast, the fast photolysis of these latter species under irradiation with UVA light in PEF led to an almost total mineralization with 98% total organic carbon decay. The effect of current density and substrate concentration on the performance of all treatments was examined. Several solar PEF (SPEF) trials showed its viability for the treatment of wastewater containing trans-ferulic acid at larger scale. Four primary aromatic products were identified by GC–MS analysis of electrolyzed solutions, and final carboxylic acids like fumaric, acetic and oxalic were detected by ion-exclusion HPLC. A reaction sequence for trans-ferulic acid mineralization involving all the detected products is finally proposed.