Application of the photo-Fenton process at circumneutral pH to agricultural water reuse

Abstract

The high water consumption in agriculture (60-70% of freshwater) and the prediction of a significant growth usage led the scientific community to the concept that the reuse of WW is necessary. Advanced Oxidation Processes (AOPs) and, in particular, photo-Fenton technique showed up to be very useful for the elimination of micropollutants (MPs) and disinfection from wastewater by generating powerful Reactive Oxygen Species (ROS). The strategy of this project consisted in involving three organic fertilizers (EDTA-Fe, EDDS-Fe and DTPA-Fe) in the application of the photo-Fenton process at neutral pH for Sulfamethoxazole (SMX) abatement (100%, 94.1% and 90.1% of SMX degradation, respectively). To be iron chelate agents, their employment permitted to avoid iron precipitation making plausible water reuse for agricultural purposes containing already a fertilizer. In this way, DTPA-Fe complex has been deeply investigated since it is the less known in scientific community so far, showing a great outcome in photo-Fenton technique application. This thesis is focus on reaction’s mechanism of the process as there would be a chance that iron complexes would participate with dissolved oxygen and sunlight to the generation of ROS, which could have significant environmental implications if they are also formed in aquatic ecosystems. From test with tert butanol as radical hydroxyl (HO∙) scavenger, this most oxidation species showed up to be the responsible of SMX degradation. Also, the introduction of solar light in the system revealed a possible iron complex excitation and radical species formation ([DTPA-Fe(II)]*2-, DTPA∙3-, O2∙-) so its engagement in reaction but at very minimum level. In addition, oxygen and hydrogen peroxide allowed the development of ROS species so increasing the efficiency of the process itself (69.2% when only H2O2 applied, 30.1% when only O2 applied).To sum up, photo-Fenton with iron complexes at neutral pH revealed to be very efficient technique in terms of reference compound removal, considering to be a possible strategy to apply in one line of WWTP (Wastewater Treatment Plant) to wastewater reuse in agriculture since the availability of solar light is free.