Textile printing and dyeing wastewater mainly refers to the wastewater containing natural impurities, fats, and organic substances such as starch generated during the processes of raw material steaming, rinsing, bleaching, and sizing. Printing and dyeing wastewater is generated during multiple processes such as washing, printing, and sizing. It contains a large amount of organic substances such as dyes, starch, cellulose, lignin, detergents, as well as inorganic substances such as alkali, sulfides, and various salts, and is highly polluting.
The textile printing and dyeing industry is a major emitter of industrial wastewater, which mainly contains pollutants, oils, salts on textile fibers, as well as various pulp, dyes, surfactants, additives, acids and bases added during the processing.
The characteristics of wastewater are high concentration of organic matter, complex composition, deep and variable color, large pH variation, and significant changes in water quantity and quality, making it difficult to treat industrial wastewater. With the development of chemical fiber fabrics, the rise of silk like fabrics, and the increasing requirements for post printing and dyeing finishing, a large amount of difficult to degrade organic compounds such as PVA slurry, artificial silk alkali hydrolysates, new dyes, and additives have entered textile printing and dyeing wastewater, posing a serious challenge to traditional wastewater treatment processes. The COD concentration has also increased from several hundred milligrams per liter to 3000-5000 mg/l.
Pulp dyeing wastewater has high chromaticity and COD, especially with the development of printing and dyeing processes such as silk blue, silk black, ultra deep blue, and ultra deep black based on foreign markets. This type of printing and dyeing uses a large amount of sulfide dyes, printing and dyeing auxiliaries such as sodium sulfide, etc. Therefore, the wastewater contains a large amount of sulfides. This type of wastewater must be pre treated with chemicals and then undergo series treatment to ensure stable and compliant discharge.
The bleaching and dyeing wastewater contains dyes, pulp, surfactants and other additives. This type of wastewater has a large amount of water, low concentration and chromaticity. If only physical and chemical treatment is used, the effluent can be between 100-200mg/l, and chromaticity can also meet the discharge requirements. However, the pollution amount is greatly increased, and the cost of sludge treatment is high, which can easily cause secondary pollution. In the case of strict environmental protection requirements, the biochemical treatment system should be fully considered. Conventional enhanced biological treatment processes can meet the treatment requirements.