Homogeneous and heterogeneous degradation of caffeic acid using photocatalysis driven by UVA and solar light

Abstract

Waste water from the wine industry is characterized by a high concentration of dissolved organic matter and the presence of natural phenolic compounds with low biodegradability. High concentrations of phenolic compounds may cause environmental pollution and risks to human health. In this article caffeic acid (CA) was used as a model compound of wine effluent because it is refractory to the conventional wastewater treatments. The oxidation of caffeic acid in water solution (0.01 g L⁻¹) by heterogeneous photocatalysis and photo-Fenton reaction was studied using UVA. The optimal conditions for each treatment were performed by multivariate experimental design. The optimal conditions for heterogeneous photocatalysis were pH 5.3 and 0.9 g L⁻¹ TiO_2. In the case of photo-Fenton treatment, optimized variable were 82.4 μmol L⁻¹ of Fe²⁺ and 558.6 μmol L⁻¹ of H₂O₂. The degradation profiles of CA were monitored by UV-Vis, HPLC, TOC and COD. To reach 90% of CA removal, 40 and 2 min of reaction, respectively, were required by heterogeneous and photo-Fenton processes, respectively. For comparison purposes, the reactions were also performed under solar light. The use of solar light does not change the efficiency of the photo-Fenton reaction, yet the performance of the heterogeneous process was significantly improved, reaching 90% of degradation in 15 min.

Keywords:

• Advanced oxidation processes
• caffeic acid
• photo-Fenton
• TiO₂
• winery wastewaters

Funding

The authors would like to thank Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT No. 1130502), CONICYT/FONDAP/15110019 and REDOC.CTA Project UCO 2102 for financial support.