Kinetics and Reaction Mechanism for Formaldehyde Wastewater Using UV-Fenton Oxidation

In photochemical reactor, the process conditions of formaldehyde wastewater treatment using UV-Fenton oxidation under the joint action of hydrogen peroxide, ferrous ions, and ultraviolet were studied, and the kinetic curves of formaldehyde degradation in different conditions were obtained. The results showed that: when the original wastewater concentration is 30mg/L, operating temperature is 23 °C, pH = 3, the dosage of H₂O₂ is suitable for 68mg/L (correspond to the theoretic oxygen requirement of wastewater 1Q_th), H₂O₂ and Fe²⁺ dosing ratio n(H₂O₂) □n (Fe²⁺) = 5, reaction to 30 minutes, the removal rate of formaldehyde is up to 91.89%. On this basis, the kinetic model for formaldehyde wastewater treatment in UV-Fenton system was established. By curve fitting and equation solving, the kinetic equation was obtained as follow: r = - (d[HCHO])/dt = 2.788×10^-2[HCHO]^0.574[Fe²⁺]^0.51[H₂O₂]^0.728. The analysis of reaction products by UV spectrum supposed that the further oxidation of the intermediate product, formic acid, is the rate-limiting step of formaldehyde oxidation reaction.