Photonic and Quantum Efficiencies for the Homogeneus Photo-Fenton Degradation of a Herbicide 2,4-D Using Different Iron Complexes

Abstract

BACKGROUND: An experimental study of the homogeneous photo-Fenton degradation of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is presented.Different sources of iron in water solution were studied: sulphate, oxalate and citrate complexes. The performances of these complexes were evaluated by means of two parameters: (i) the photonic efficiencies of degradation and mineralization; and (ii) the quantum efficiencies of degradation and mineralization. Moreover, in order to quantify the consumption of the oxidizing agent, two parameters were also defined and evaluated: the initial specific consumption of the hydrogen peroxide and the minimum hydrogen peroxide consumption for complete mineralization. RESULTS: For pH=5 and T =35ºC, the degradation photonic efficiency using ferric sulphate was 6 times lower than that obtained with the ferric citrate.On the contrary, at pH=5, quantum efficiencies of mineralization close to 50% for citrate and oxalate complexes were attained. For pH=5 and 25 or 35ºC, the initial specific consumption of hydrogen peroxide for the ferric sulphate was 5 times higher than those of the remaining complexes. However, considering all the operating conditions, the minimum hydrogen peroxide consumption for completemineralization using the oxalate complex was always lower than or at most similar to those observed in the other two complexes. CONCLUSION: Using different sources of iron, the influence of pH and temperature on the pollutant degradation and mineralization process was determined. For pH=5 and both temperatures, the ferric sulphate system required more than twice the time to achieve complete degradation of the herbicide. Moreover, mineralization only reached 55% after 180 min operation.