Gaining further insight into photo-Fenton treatment of phenolic compounds commonly found in food processing industry

A mixture of eight phenolic compounds, namely 2,4-dinitrophenol, tannic, ellagic, gallic, protocatechuic, vanillic, syringic and sinapic acids, have been treated by means of a photo-Fenton process under simulated and real sunlight. An experimental design methodology, based in Doehlert matrixes, was employed to check the effect of the concentration of Fe(II) and H2O2, as well as pH. Response surfaces show that photo-Fenton can be extended to pH values clearly above 2.8, probably due to complexation of iron with the phenolic substances. Experiments performed under solar irradiation at pH=3.9 showed that complete removal of the monitored pollutants was achieved in less than 3min; mineralisation was also efficient, although some organics remained in the solution. Toxicity was monitored according to Pseudokirchneriella subcapitata and Daphnia magna bioassays; Recombinant Yeast Assay (RYA) was employed to assess estrogenic and dioxin-like activities. 2,4-Dinitrophenol was demonstrated to be the major concern and, in general, photo-Fenton resulted in a detoxification of the solution. Finally, excitation emission matrix (EEM) fluorimetry was employed to obtain complementary information on the behaviour of organic matter. Most peaks associated with the parent pollutants disappeared after short irradiation periods and, at 12min of irradiation chromophores were destroyed, what can be associated with the removal of complex molecules.