Photodegradation of Reactive Blue 4 solutions under ferrioxalate-assisted UV/solar photo-Fenton system with continuous addition of H2O2 and air injection

An experimental study based on the homogeneous ferrioxalate-assisted solar photo-Fenton process shows the effect of the continuous addition of hydrogen peroxide and air injection on the degradation of non-biodegradable dye Reactive Blue 4 (RB4) solutions. The reaction was carried out in a CPC (compound parabolic collector) solar pilot plant reactor. It was shown that the degree of dye solution mineralization was enhanced because the scavenger effect of H2O2 was minimized. Air bubbling had a negative effect because oxygen reacted with oxalyl radical anions, diminishing the amount of generated Fe(II), and consequently the concentration of hydroxyl radicals produced under irradiation of oxalate in the presence of peroxide was lower. In addition, this system permits the use of lower concentrations of ferrous ion, reducing the costs of the later iron removal process. Under the optimal conditions selected in this system, TOC removal was increased from 61% to 82% with a shorter reaction time as compared with a peroxide dose at the beginning of the reaction. The efficiency of the mineralization of RB4 solutions was enhanced when the solar CPC reactor worked together with an artificial UV-A/C pilot plant, increasing TOC removal up to 95%. Artificial UV lamps can be used either to improve the process or as an alternative to solar CPC on cloudy days.