Printing and dyeing wastewater is discharged from printing and dyeing plants mainly processing cotton, hemp, chemical fibers, and their blended products. Printing and dyeing wastewater has a large volume, with each ton of textile processing consuming 100 to 200 tons of water, of which 80 to 90% becomes wastewater.

Characteristics of Wastewater:

Printing and dyeing wastewater is one of the more difficult industrial wastewaters to treat. It has characteristics such as high COD concentration, high color, high salt content, difficulty in biodegradation of organic matter, and significant variations in water quality and quantity over time (intermittent discharge of wastewater). The prominent issue in printing and dyeing wastewater treatment is the removal of color and refractory organic matter.

Treatment Methods:

The treatment of printing and dyeing wastewater typically adopts a process mainly consisting of hydrolysis acidification, biological contact oxidation, and biological charcoal. This treatment process has been widely used and matured in recent years for printing and dyeing wastewater treatment. The purpose of hydrolysis acidification is to hydrolyze and acidify certain poorly biodegradable high-molecular-weight substances and insoluble substances in printing and dyeing wastewater into small molecular substances and soluble substances, thereby improving the biodegradability and B/C value to create conditions for subsequent aerobic biodegradation. Meanwhile, the residual sludge generated from aerobic biodegradation is returned to the anaerobic digestion stage through sedimentation tanks, reducing the discharge of residual sludge from the entire system, thus achieving the balance of its own sludge. Both the anaerobic hydrolysis acidification tank and the biological contact oxidation tank are equipped with fillers, belonging to the biological film method treatment. The biological charcoal tank is filled with activated carbon and supplied with oxygen, combining characteristics of suspended growth and attached growth methods. The purpose of pulsating water inflow is to agitate the anaerobic hydrolysis acidification tank.