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

Abstract

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℃, pH = 3, the dosage of H 2 O 2 is suitable for 68mg/L (correspond to the theoretic oxygen requirement of wastewater 1Q th ), H 2 O 2 and Fe 2+ dosing ratio n(H 2 O 2 ) n (Fe 2+ ) = 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: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.

Combined AOPs for Formaldehyde Degradation Using Heterogeneous Nanostructured Catalysts

“…For ferrous sulfate, based on mass balance calculation, a 4% w/w solution in ethanol should be enough to have the same catalyst content of titania and similar to that used in literature for a homogenous photo-Fenton system [11]. However, due to a partial loss of FeSO 4 experienced during the electrospray process, owing probably to an interaction of the Fe 2+ with the electric field, a 10% w/w FeSO 4 solution in ethanol has to be used.…”

“…Concentrations of catalysts, in both homogeneous and heterogeneous experiments, have been fixed based on optimal compositions reported in literature [11] or based on our previous experience [32]: for homogeneous catalysis, FeSO 4 and H 2 O 2 were used at 24 and 400 ppm, respectively, while in the heterogeneous supported system around 0.15 mg/cm 2 of catalyst has been deposited (the exact values are obtained by thermogravimetric analysis (TGA) and are reported in the following).…”

“…However, it was evident that after 4 h the abatement of the formaldehyde content was still low. The addition of H2O2 (400 ppm, according to optimal content reported in [11]) in aqueous solution to the PAN-TiO2 system (PAN_TiO2 + H2O2 in Figure 6) resulted in greater oxidation with respect to neat PAN-TiO2 and this was likely attributed to the enhanced charge separation induced by H2O2 as an electron acceptor and the reductive conversion of H2O2 to OH• [7]. Moreover, the The degradation of the methanol can start as soon as a hydroxyl radical is produced and it may compete with formaldehyde to consume hydroxyl radicals resulting in the retardation of the oxidation reaction of formaldehyde.…”

“…In photo-Fenton processes (i.e., whenever Fe was present) the pH has been adjusted to 3 using 0.2 N sulfuric acid. When ferrous sulfate and H 2 O 2 were used in solution, their concentrations were 24 and 400 ppm, respectively, i.e., set at the optimal conditions identified elsewhere [11]. The heterogeneous PAN-Fe catalyst comprised 0.12 mg/cm 2 of FeSO 4 (i.e., similar content to the TiO 2 content of the previous experiment, i.e., optimal composition defined elsewhere [32]), which corresponded to a total of 6 mg of ferrous sulfate in the system.…”

“…Fenton and photo-Fenton processes have already been proposed for formaldehyde removal from wastewater [11][12][13]. In general, the Fenton and photo-Fenton processes require the use of ferrous ions (Fe 2+ ) and hydrogen peroxide (H 2 O 2 ) [14].…”