Effect of light source on the catalytic degradation of protocatechuic acid in a ferrioxalate-assisted photo-Fenton process

The catalytic degradation of protocatechuic acid (PA) solutions in a ferrioxalate-assisted photo-Fenton process irradiated with solar or artificial ultraviolet light sources was investigated. The reactions were carried out either in a pilot plant consisting of a compound parabolic collector (CPC)-solar reactor or in a UV-A/C-lamp reactor. An optimization study was performed using a multivariate experimental design including the following variables: pH, temperature, solar power, air flow and initial concentrations of H2O2, Fe(II) and oxalic acid. The photocatalytic degradation efficiency was determined by measuring the elimination of the original PA and the removal of total organic carbon (TOC). TOC-removal rates of 97% and 96% were achieved under artificial UV-A/C and solar light, respectively, but with different optimum operating conditions. When artificial UV light was used in the presence of oxalic acid, the degradation rate was higher in the UV-C system than in the UV-A system because ferrioxalate complexes are primarily formed at 200–280 nm. OH radicals were the main oxidative intermediate species in the artificial UV-A/C process while superoxide and OH radicals played the most significant roles in the solar process. Artificial UV-A/C light can be used as an alternative to solar CPC on cloudy days.