Effect of volumetric rate of photon absorption on the kinetics of micropollutant removal by solar photo-Fenton with Fe3+-EDDS at neutral pH

To run the photo-Fenton process at circumneutral pH as a tertiary wastewater treatment, the use of chelating agents, such as ethylenediamine disuccinic acid (EDDS), has been proposed. For the design and optimization of photocatalytic reactors, the concept of volumetric rate of photon absorption (VRPA) is very useful, since it combines the effects of light absorption and reactor geometry. This research is focused on the study of the effect of VRPA of the Fe3+-EDDS complex on the kinetics of micropollutant removal by solar photo-Fenton at neutral pH. To this end, experiments were carried out at different values of VRPA, from 383 to 1933 mu E m(-3) s(-1), using the pesticide acetamiprid (ACTM) as a model pollutant at an initial concentration of 100 mu g L-1. Despite instability of the complex with light, high removal percentages were achieved for short reaction times with 0.1 mM Fe3+-EDDS. Due to the higher absorptivity of the complexed iron, the process became photosaturated at higher values of VRPA than those reported at pH 2.8 for Fe3+ allowing to work under photolimitation conditions at shorter optical path lengths than at acidic pH. The higher absorptivity of the complexed iron at neutral pH than Fe3+ at pH 2.8 allowed to work under photolimitation conditions at shorter optical path lengths because the process became photosaturated at higher values of VRPA. Nonetheless, a 50% increase in the treatment capacity was achieved by increasing the liquid depth by three times. As far as the authors know, this is the first work that quantitatively describes the effect of the radiation and the optical path length on micropollutant removal with Fe3+-EDDS.