Changes of dissolved oxygen during the caffeine oxidation by photo-Fenton

The aim of this work is to analyse the changes of dissolved oxygen ([DO], mg/L) during the oxidation of caffeine waters by photo-Fenton treatment. The concentration of dosed hydrogen peroxide would be the addition of the stoichiometric [H2O2], which reacts with organic matter ([H2O2]esteq=2.0 mM), plus the concentration in excess of [H2O2]exc that decomposes, generating O2 through radical processes, according to a ratio R=0.8164 mmol H2O2/mg O2). Operating at doses lower than the stoichiometric value [H2O2]0<2.0 mM, O2 is not emitted, as there is no excessive oxidant. Besides, it is verified that the Fe2+ ion is oxidized to Fe3+, with subsequent regeneration to Fe2+. Applying higher doses than the stoichiometric [[H2O2]0>2.0 mM, oxygen is released, and regeneration of Fe3+ to Fe2+does not occur. The highest oxygen generation output is obtained when dosing [Fe]0=10.0 mg/L, conducting at pH=3.0 and 25ºC. The evolution of DO formation is adjusted to zero-order kinetics, the kinetic constant of oxygen generation being kf=29.48 [Fe]0-1.25 (mg O2 L-1 min -1) and oxygen consumption kd=-0.006 [Fe]02.0 + 0.244 [Fe]0-3.7 (mg O2 L-1 min-1).