Advantages of using coagulation and sedimentation (flotation) in decolorization of printing and dyeing wastewater Description The advantages of using coagulation and sedimentation (flotation) in decolorization of printing and dyeing wastewater indicate that our country's dye industry has the characteristics of small quantities and varieties and most of them are intermittent Operation, intermittent discharge of wastewater, water quality and water changes in a wide range. Long dye production process, low product yield, complex wastewater components, high concentration (COD 1000 ~ 100,000 mg / L), deep color (500 to 500,000 times). Most of the organic components in wastewater are aromatics and heterocyclic compounds as precursors, with a chromogenic group and a polar group. Wastewater also contains more raw materials and by-products, such as halide, nitro, aniline, phenols, etc., and inorganic salts such as NaCl, Na2SO4, N a2S and so on. Due to the variety of dye production, and toward the anti-photolysis, anti-oxidation, anti-biological oxidation direction, so that dye wastewater treatment more difficult. Difficulties in the treatment of dye wastewater: First, COD high, while the BOD / COD value is small, poor biodegradability; the second is the high color, and complex components. COD removal and decolorization are related, but decolorization problems more difficult. Direct dyes are generally double azo, trisazo or stilbene type structure, high molecular weight hydrophilic groups, good water solubility, solubility, direct dye molecules in aqueous solution generally linear, a few aromatic The rings are in the same plane. Dye molecules can associate with each other through the hydrogen bonds of the groups, have a tendency of aggregation, exist in the colloidal form in the aqueous solution, and are easily removed by the chemical coagulation method. At present, in the common printing and dyeing wastewater decolorization method, the coagulation and sedimentation (flotation) method is widely used due to the advantages of technical investment, simple equipment and small occupation area. In the printing and dyeing wastewater used in many coagulant, can be roughly divided into two types of inorganic coagulant and organic coagulant. In the coagulation process, the coagulant first hydrolyzes in the water, (polyaluminum chloride, polymerized ferric sulfate, etc.) polymerization and other chemical reactions, the resulting hydrolysis, the polymerization product and then the water particles electrostatic neutralization, intergranular plus Bridge, adhesion roll sweep and other effects, to generate coarse coagulation and then removed by precipitation. The above several effects may occur at the same time, under different conditions may play a dominant role. Printing and dyeing wastewater dye chromophore is through the complex process to complete the decolorization. The coagulation method is the key to the selection of coagulant, dosing less, easy management, and can get the best economic effect of the coagulant is the most viable.