Printing and dyeing wastewater is mainly polluted by pigments and coagulum. Then, decolorization treatment is also its main treatment condition. Printing and dyeing decolorization is different from the decolorization of clothing that we usually say. The best printing and dyeing decolorization method is not bleaching powder.
Physical decolorization of printing and dyeing wastewater
In the sewage, physical methods are used for decolorization, and activated carbon is widely used as an adsorbent. Activated carbon is different from chemical bleach, ferrous sulfate and other agents. It will not damage the structure of the dye while removing the color. It is currently the best decolorizing agent for printing and dyeing. But its treatment effect is largely affected by the PH value of printing and dyeing wastewater. Its adsorption and decolorization of acid dyes and sulfur dyes is relatively weaker than that of basic dyes and direct dye wastewater.
Chemical decolorization of printing and dyeing wastewater
Decolorization is achieved through a chemical reaction, which is called chemical decolorization. The commonly used methods are oxidation and adsorption. The bleaching powder decoloration we mentioned earlier is the chlorine oxidation decolorization treatment. The decolorization principle of oxidizing decolorizing agents such as bleaching powder is to destroy the structure of color-developing organic matter in wastewater. After the dye in the wastewater is oxidized and decolorized, some dyes will exist in an oxidized state, and a reduction and recovery reaction will occur under certain conditions. Therefore, this method is not used alone for dyeing and decolorization.
Chemical adsorption is another very common method in printing and dyeing decolorization. It is to use ferrous sulfate, polymeric ferric sulfate and other chemical agents with adsorption effect to remove colored dyes in wastewater by adsorption and precipitation. After the dye in the wastewater is treated by this method, it is mixed with the sludge in the water and separated by the sludge to achieve the decolorization effect. Compared with the oxidative decolorization method, this method of decolorizing by ferrous sulfate and other agents has no risk of recovery.
Ferrous sulfate has the advantages of low cost and convenient operation, and also has relative durability in the decolorization of wastewater. However, in printing and dyeing wastewater, it is not as safe and efficient as activated carbon. Activated carbon is non-renewable and expensive. It is generally only used for high-concentration and low-water decolorization of printing and dyeing. Ferrous sulfate is currently the most commonly used treatment for decolorization of printing and dyeing wastewater Medicament.