Study On Treatment Of High Concentration Phenol And Formaldehyde Wastewater By Photocatalytic Oxidization

The UV/Fenton process is an advanced oxidation process, by which the poisonous substances in wastewater can be degraded. In this study, an apparatus for the Photo-assisted Fenton decomposition of phenol and formaldehyde wastewater was established and the oxidative decomposition process was studied with the emphasis on its influence factors, affecting mechanism, the kinetics and the conditions of the techniques.Based on the analysis of the conclusion of preliminary experiments, orthogonal experiments were designed to optimize four selected influence factors of PH, concentration of H2O2, concentration of Fe2+ and reaction time. According to the rank of those factors in the decreasing order, we designed the basic operating conditions of the Fenton and UV/Fenton processes in the single factor experiments: H2O2 = 6mL, FeSO4·7H2O = 2g, PH=4,t=30min,T=30OC. The results indicate:①The substantive mechanism is that hydrogen peroxide was decomposed into hydroxyl radical rapidly with the UV and iron ions as the catalysts. The hydroxyl radical can decompose the phenol and formaldehyde in a short time and the degradation of the COD can be higher than 90%.②The UV/Fenton process had the higher degradation rate of the phenol,formaldehyde and COD than the Fenton process. The reason is that the Fe3+ can be converted into the Fe2+ by the UV ,and form a circular reaction of Fe(Ⅱ)/Fe (Ⅲ),therefore,it is very advantageous to the degradation of the organic pollutants.During the experiments, we observed that with the increasing amount of the H2O2, the color of the wastewater of the phenol and formaldehyde changed from the deep brown into the yellow. The degradation mechanism of the phenol is seemed as: phenol → benzoquinone → maleate → oxalic acid,Malonate → propanoic acid,acetic acid,formic acid → CO2,H2O and that of the formaldehyde is the formic and oxalic acid and so on. We can learn from the dynamical theory that the low-molecular-weight organic acids have higher activation energy, so their conversions to the CO2 and H2O are the rate-limiting steps.The paper also compared the treatment of organic wastewater by homogeneous-phase oxidation technology, including UV / H2O2,UV / H2O2 /Fe2+,H2O2 /Fe2+and H2O2.The results showed that the effective degradation could be observed in the UV/Fenton process, and the degradation rate of the Fenton process was lower than the UV/Fenton process.The degradations of COD by UV/H2O2 and H2O2 were not notable.Through the alteration of the concentration of the catalyst and oxidant, the dynamics of the phenol and formaldehyde oxidized by the UV/Fenton process were studied. The correlativity of the reaction time and the relative degrading rate of the COD was analyzed and a simplified mechanistic model for the organic wastewater of the phenol and formaldehyde was derived. The kinetic reaction equation was fitted as follows:...