Characteristics and treatment status of printing and dyeing wastewater

Printing and dyeing processing is an indispensable and important process in the textile industry. Whether it is silk, cotton and linen, or knitting and wool spinning, printing and dyeing problems will be more or less involved in the processing process.

In recent years, with the continuous updating of printing and dyeing technology, the use of chemically synthesized slurries and auxiliaries has spread throughout large and medium-sized printing and dyeing plants. Correspondingly, the water quality of printing and dyeing wastewater has long been no longer limited to high COD, high chroma, and low biodegradability. specialty. As the raw materials used by various textile printing and dyeing enterprises are quite different, the microscopic components in the wastewater are naturally quite different. Some printing and dyeing wastewater also contains toxic substances such as high ammonia nitrogen and chromium. Therefore, it is necessary to carry out a detailed scientific experimental analysis of the printing and dyeing wastewater according to the difference of the discharge source, and optimize the operating parameters in the treatment to obtain the best treatment effect.

Printing and dyeing wastewater treatment technologies

At present, the main treatment methods of printing and dyeing wastewater include three categories: physical chemical treatment, chemical treatment and biological treatment. The following will analyze the application of various treatment technologies in the treatment of printing and dyeing wastewater.

1. Physical and chemical treatment method

In the treatment of printing and dyeing wastewater, the commonly used physical and chemical treatment methods mainly include adsorption method and membrane separation method.

Adsorption method

The adsorption method refers to the method of removing the dark color and various substances in the printing and dyeing wastewater by using the adsorption capacity of the surface porous solid substances such as activated carbon, clay minerals and fly ash. Materials used in adsorption methods generally have strong acid and alkali corrosion resistance and chemical stability. When pollutants come into contact with solids, they will be attracted and attached to their surfaces. However, since the solid matter is easily saturated and the regeneration cost is high, this technology is generally suitable for a small amount of low-concentration or multiple advanced treatment of printing and dyeing wastewater.

Membrane separation method

Membrane separation method, also known as the use of membrane method, is an emerging printing and dyeing wastewater treatment technology developed in recent decades - through semi-permeable membranes with different pore sizes, the mixture is separated and filtered according to particle size. According to the different functions of separation, the method is divided into four aspects: microfiltration, ultrafiltration, nanofiltration and reverse osmosis.

Although the membrane separation method has stable water output, easy operation, environmental protection and energy saving, because the separation membrane can only be used once and the cost is relatively high, this technology is mainly used in large-scale textile printing and dyeing factories with strong economic ability.

2. Chemical treatment

The chemical treatment method of printing and dyeing wastewater uses the principle of chemical reaction to achieve the purpose of separating pollutants or changing the properties of harmful substances in wastewater to make them harmless. The commonly used technologies are flocculation sedimentation, chemical oxidation and electrochemical methods.

Flocculation sedimentation method

Add flocculants and coagulants to the printing and dyeing wastewater, and then apply external force to make the above colloidal substances collide and polymerize with the small molecule suspended matter in the wastewater until flocculent particles with larger particle size are formed, and finally settle or float with air. way to filter it out. This technology has low cost, and the flocculant made of natural polymer materials has no toxicity, mild reaction and convenient degradation. When it is used in the treatment of printing and dyeing wastewater, the CODcr removal rate is greater than 91% and the decolorization rate is greater than 99%. It is a widely used wastewater treatment technology in medium-sized textile printing and dyeing factories, but the decolorization effect of this technical method is still not ideal when facing highly water-soluble dyes.

Chemical oxidation

Common chemical oxidation methods include chlorine oxidation, ozone oxidation, photocatalytic oxidation and wet oxidation. The group is broken, and at the same time of decolorization, the organic molecules in the water body are converted into safe substances, and the water quality of the printing and dyeing wastewater is improved. However, in addition to the advantages of high treatment efficiency, fast oxidation speed, and no secondary pollution, chemical oxidation has poor decolorization effect on insoluble dyes in printing and dyeing wastewater.

Electrochemical method

At present, the electrochemical method is mainly used in the wastewater treatment technology of textile printing and dyeing plants. It has excellent decolorization effect, low operating cost, and convenient operation and management. On the basis of removing COD from wastewater, it can significantly improve its efficiency Biochemical properties are usually used as a pretreatment method to lay the foundation for the subsequent treatment of printing and dyeing wastewater.

3. Biological method

With the development of modern textile printing and dyeing technology, there are some soluble substances in the printing and dyeing wastewater that cannot be completely degraded by traditional physical and chemical technologies, and the use of microorganisms in nature can often solve this problem efficiently. At present, the common biological treatment methods include aerobic method, anaerobic method and bacterial injection method.

Generally speaking, the printing and dyeing wastewater treated by aerobic method can often obtain better BOD treatment effect, but the removal rate of COD and chroma is not ideal, and in terms of degrading organic matter, anaerobic method is superior to aerobic method bigger. Therefore, in recent years, the biodegradability of printing and dyeing wastewater is improved by hydrolysis and acidification by anaerobic method, and then the wastewater treatment technology in series by aerobic method is being widely used by textile printing and dyeing plants.

Summarize

With the development of environmental protection in the new era, people's awareness of protecting the environment and water resources has gradually increased, and the treatment of printing and dyeing wastewater has also attracted more and more attention as part of water pollution control. For printing and dyeing wastewater, because its composition and concentration are different from other industrial wastewaters, it is difficult to meet the increasingly strict effluent discharge requirements of the country with simple physical and chemical methods or biological methods. , should be based on the principle of fully analyzing the pollution element composition of wastewater, and combine a variety of treatment technologies.