Role of sunlight and oxygen on the performance of photo-Fenton process at near neutral pH using organic fertilizers as iron chelates

Abstract

Nowadays, reaction mechanisms of photo-Fenton process with chelated iron are not yet clearly defined. In this study, five organic fertilizers were used as iron complexes to investigate the role of sunlight and oxygen in photo-Fenton at near neutral pH. UV absorbance and stability constant of each selected iron chelate is different, and this work demonstrates that these parameters affect the reaction mechanisms in SMX degradation. Irradiation experiments without H2O2 revealed that only EDDS-Fe and DTPA-Fe achieved SMX degradation, but different iron release. These results, together with soluble oxygen free experiments, allowed the proposal of complementary reaction mechanisms to those of the classical photo-Fenton. The proposed mechanisms start through the potential photoexcitation of the iron complex, followed by subsequent oxygen-mediated hydroxyl radical generation reactions that are different for EDDS-Fe and DTPA-Fe. Moreover, irradiation experiments using EDTA-Fe and HEDTA-Fe had negligible SMX degradation despite iron release was observed, evidencing the differences between iron chelates.