Kinetic study of the photo-Fenton degradation of formic acid: Combined effects of temperature and iron concentration

This study is focused on the kinetic modelling of the Fenton and photo-Fenton degradation of a model pollutant (formic acid) in aqueous solution, for relatively low iron concentrations (1–9 ppm). The reaction rate expressions are derived from an accepted reaction mechanism and explicitly having into account the local volumetric rate of photon absorption. The experimental work was performed in a well-stirred tank laboratory reactor irradiated from the bottom. Afterward, the proposed kinetic model and the experimental data were used to estimate the Arrhenius parameters between 20 and 55 °C, applying a non-linear regression procedure. To avoid the precipitation of iron compounds during the experimental runs, simultaneous high reaction temperatures (55 °C) and iron concentrations (9 ppm) were prevented. To achieve this goal, an experimental design based on the D-optimality criterion was adopted. The proposed kinetic model was able to reproduce the combined effects of changing the ferric iron concentrations, reaction temperatures, and formic acid to hydrogen peroxide molar ratios on the pollutant degradation rate. Kinetic model predictions are compared with experimental data of the organic compound conversion, and a good agreement is obtained. For the whole set of Fenton and photo-Fenton experimental runs, the maximum root mean square error is 7.64%.