Formaldehyde is a colorless, intensely irritating gas. Soluble in water, alcohol and ether. 35 ~ 40% formaldehyde solution is called formalin. Formaldehyde is an important organic raw material, mainly used in the plastics industry, synthetic fiber, leather industry, pharmaceuticals, dyes and wood adhesives production process. Hazard: Formaldehyde is very toxic to humans and warm-blooded animals. It can irritate the skin and easily lead to dermatitis. It is easy to cause respiratory irritation, allergy, lung dysfunction, abnormal liver function and immune dysfunction. Long-term human consumption of formaldehyde contaminated water can cause dizziness, anemia and various neurological diseases. Due to the wide range of uses of formaldehyde in industrial production, complete restrictions are not realistic and the production of formaldehyde wastewater must be treated. National Standard "Integrated Wastewater Discharge Standard" (GB8978-1996) provides that the formaldehyde content of secondary emission standards shall not exceed 2mg / L. However, formaldehyde can directly react with the proteins, DNA and RNA in the microorganism, resulting in the death of the microorganism or inhibiting the biological activity. When the concentration exceeds 200 mg / L, the activity of the microorganism is almost completely inhibited. Therefore, the high concentration of formaldehyde is not suitable for the biological treatment. Solution morphology is true solution, coagulation process is also difficult to work. Introduction of formaldehyde wastewater pretreatment method Researchers at home and abroad have made a great deal of research on the treatment technology of formaldehyde wastewater. Formaldehyde wastewater treatment methods are: oxidation, biological treatment, stripping, condensation, lime and so on. 1, oxidation method Fenton's reagent oxidation of formaldehyde wastewater is a commonly studied method by domestic and foreign scholars. The reagent is a kind of strong oxidant consisting of H2O2 and Fe2 +. It oxidizes and deoxidizes the organic matters in waste water mainly by highly active hydroxyl radicals (OH), and completely degrades the organic substance in a short time. 2, wet oxidation method In the absence of added catalyst, the formaldehyde-containing wastewater is selectively oxidized to CO2 and H2O at 180 to 315 Â° C and 2 to 15 MPa without the generation of nitrogen oxides, sulfur oxides, Hydrogen chloride, fly ash and so on. With CuO-ZnO / Al2O3 catalyst, the reaction time is shortened, the temperature and pressure can be reduced to 130 ~ 250 â„ƒ and 1 ~ 5MPa. According to relevant research shows that the removal rate of formaldehyde and CODCr up to 90%. 3, photocatalytic oxidation method Photocatalytic oxidation technology, is from the 1970s and gradually developed a new environmental technology. It utilizes the properties of semiconductor oxide materials that can be activated by light in the surface and can effectively oxidize and decompose organic compounds, reduce heavy metal ions, kill bacteria and eliminate odors, especially the most commonly used TiO2 system. In 1974, Honda et al. First discovered that TiO 2 can decompose water into H 2 and O 2 under light irradiation. Photocatalytic oxidation is rapidly applied to wastewater treatment, especially to various organic materials that are hard to degrade. Research shows that photocatalytic oxidation can effectively deal with low concentrations of formaldehyde wastewater. Removal rate of 90% or more.