The wastewater treatment of printing and dyeing enterprises basically adopts the coagulation decolorization technology to treat the wastewater. In the purification treatment of printing and dyeing wastewater, disperse dyes, vat dyes, sulfide dyes and some water-soluble dyes with large molecular weight can be decolorized by coagulation. For the dyeing wastewater with small molecular weight, such as acid dyes, reactive dyes, etc The decolorization effect is poor. The molecular structure of dye directly affects its charged state, aggregation state and dyeing mechanism in water, which are the important factors affecting the effect of coagulation decolorization of printing and dyeing wastewater. Therefore, effective coagulation decolorization technology should focus on the molecular structure of dye, and a variety of new coagulation decolorization technologies can be developed from the molecular structure and spatial configuration of dye.

A large number of repetitive experiments were carried out to study the effect of ferrous sulfate dosage on the chromaticity and COD of printing and dyeing wastewater It is found that ferrous sulfate can maintain good and stable coagulation effect on printing and dyeing wastewater with different colors, and reduce the COD value of raw water. Because the dye molecules in raw water also contain amino groups, poor groups and other groups, these groups have not shared electron pairs, which are very strong standard. After adding ferrous sulfate, it will react with ferrous ion to form complex macromolecular complex, reduce its water solubility and make dye molecules have colloidal properties. Then, it will be removed by coagulation of ferrous ion hydrolysate. From the experimental results, when the dosage of ferrous sulfate is 0.8g/l, the removal rates of raw water chromaticity and cod are 58.7% and 81.6%. When the dosage is increased, the color and COD removal rate of raw water have little change, so the dosage of ferrous sulfate is 0.8g/l raw water.