Optimization of combined process for high standard discharge of printing and dyeing wastewater

With the scientific and technological progress and continuous innovation of the textile printing and dyeing industry, new changes have taken place in the water quality characteristics and treatment technology of printing and dyeing wastewater. Based on the analysis of the printing and dyeing process flow and the characteristics of printing and dyeing wastewater, China has a large amount of printing and dyeing wastewater discharge every year. The characteristics of printing and dyeing wastewater determine that it is difficult to treat.

Therefore, it is necessary to deeply study the advanced treatment process of printing and dyeing wastewater in order to recycle printing and dyeing wastewater and ease the tense situation of water resources in China. This paper briefly analyzes the status quo and development direction of advanced treatment process of printing and dyeing wastewater, hoping to provide some valuable reference.

Printing and dyeing wastewater is a kind of industrial wastewater which is difficult to treat because of its high chromaticity, high organic content, complex composition and poor biochemical performance. The state pays more and more attention to ecological environment protection, and has increasingly strict control over wastewater discharge standards and total regional wastewater discharge. With the scientific and technological progress and continuous innovation of the textile printing and dyeing industry, the use of chemical synthetic raw materials has increased greatly, making the quality of printing and dyeing wastewater diversified and complex. In view of this situation, it is necessary to deeply treat printing and dyeing wastewater to ease the tension of water resources.

1、 Analysis of the characteristics of printing and dyeing wastewater

Specifically, the mixed wastewater discharged in the production process of various textile printing and dyeing enterprises is called printing and dyeing wastewater. The printing and dyeing wastewater includes production wastewater, domestic water and other components, and the water quality is constantly changing. Specifically, printing and dyeing wastewater has the characteristics of higher organic pollutant content, greater alkalinity, darker chroma, greater difference in pollutant composition, etc. In the new era, the development of chemical fiber fabrics is accelerating, and more toxic organic substances, including new auxiliary size, are introduced into printing and dyeing wastewater, which greatly increases the difficulty of advanced treatment of printing and dyeing wastewater.

2、 Advanced treatment technology of printing and dyeing wastewater

1. Adsorption method

At present, in the advanced treatment of wastewater, the adsorption method has been widely used, which mainly uses the adsorption capacity of porous solid materials to effectively remove a variety of substances in the sewage.

Among them, activated carbon is widely used in the advanced treatment of printing and dyeing wastewater. It has strong resistance to strong acid and alkali corrosion, can effectively resist water immersion, high temperature, high pressure, etc., and has good adsorption performance and chemical stability. Therefore, its application field is expanding. With the development of science and technology, other types of new adsorbents have emerged.

The coagulation sedimentation plus activated carbon adsorption process is developed into the modified magnetic particle adsorption combined with chlorine dioxide oxidation treatment technology. The results show that it has a good effect, can significantly reduce the mass concentration and chromaticity of wastewater, and does not require high economic costs.

Yang Zhanhong uses the activated carbon combination method to treat printing and dyeing wastewater, which has a high removal rate of organic pollutants and a low mass concentration. # It should be noted that although activated carbon can effectively remove the chromaticity and organic pollutants in printing and dyeing wastewater, it has a greater difficulty in regeneration. After regeneration, it will also significantly reduce its adsorption capacity, which has a greater restriction on the application scope of activated carbon.

2. Membrane separation

The membrane separation technology is a purely physical process. The membrane will not change the phase and does not need to add other catalytic substances. The operation cost is low, the effluent is stable and the effect is good. However, the disadvantage of this method is that the one-time cost is high and the membrane pollution is serious. Different pretreatment methods need to be selected according to the type of wastewater. Proper removal of suspended solids in the pretreatment unit can increase the life of the membrane, but these operations will increase the cost budget and limit the promotion and application of membrane technology.

3. Biological method

The study found that the biological method is less difficult to operate, does not require high operating costs, and there is no secondary pollution. Therefore, it is widely used in the treatment of printing and dyeing wastewater. This technology mainly uses aerobic and anoxic bioreactors to effectively treat printing and dyeing wastewater through interception, filtration, adsorption, biological metabolism and other links.

Compared with ordinary activated sludge method, this method has greater advantages, such as no need for large floor area, strong impact load resistance and oxygen transmission efficiency. Some people use two cascades of ozone oxidation to deeply treat printing and dyeing wastewater. The results show that the removal rate is more than 345, and the chromaticity is significantly reduced.

3、 Effect of combined process on dyeing wastewater treatment

At present, the combination of physico-chemical and biochemical processes is the mainstream process for the treatment of printing and dyeing wastewater. Generally, the three-stage treatment process - the first stage treatment is mainly coagulation, which uses inorganic and coagulant organic formaldehyde dicyandiamide polymer coagulants to remove large fiber particles and other easily settled impurities. The second stage treatment is mainly biological method. The printing and dyeing wastewater has poor biodegradability, and only aerobic treatment is easy to cause sludge bulking.

At present, hydrolysis acidification aerobic treatment method is often used to improve the biodegradability of wastewater through anaerobic acidification, and then remove organic pollutants through aerobic process. The tertiary treatment is mainly based on advanced oxidation technology, which makes use of the highly efficient oxidation effect produced by ozone, photocatalyst reagents, etc. on water bodies; And chroma, the components of printing and dyeing wastewater are complex,

Local standards are becoming stricter, which makes wastewater treatment more difficult.

At present, most of the printing and dyeing wastewater treatment processes are aimed at the treatment of mixed wastewater. The characteristics of wastewater in different processes are not considered, and the treatment of different types of printing and dyeing wastewater is not targeted enough. The water quality of high concentration wastewater and low concentration wastewater in pretreatment is different, The selection of treatment process is not targeted - the refractory organic matter in printing and dyeing wastewater is the main factor that restricts the wastewater to reach the new standard and realize recycling&In the process of selecting the printing and dyeing wastewater treatment process, we should consider the characteristics of different methods according to the actual wastewater situation, and scientifically select the combined process to achieve the removal effect. Researchers at home and abroad have designed different combined treatment processes, The combination process has become the main method of dyeing wastewater treatment.

The printing and dyeing wastewater of the wool factory is treated by the membrane reactor, which adopts the continuous infiltration method. The treated effluent quality can reach the average removal rate of turbidity and color in the recycled water reuse standard sewage in China, respectively, and the coagulation composite biological tank and coagulation contact oxidation combined process, which have shown good effect in the treatment of low concentration printing and dyeing wastewater, and the removal effect of color can reach about, The research on the combination process of printing and dyeing wastewater not only has good effect when applied to low concentration or simulated printing and dyeing wastewater, but also has ideal removal efficiency for high concentration wastewater.

At present, most of the printing and dyeing wastewater treatment processes are aimed at the treatment of mixed wastewater. The characteristics of wastewater in different processes are not considered, and the treatment of different types of printing and dyeing wastewater is not targeted enough. The quality of high concentration wastewater and low concentration wastewater in pretreatment is different, and the selection of treatment process is not targeted. To solve this problem, anaerobic hydrolysis anaerobic fluidized bed is selected as the pretreatment process of high concentration water, After mixing the effluent with low concentration water, it is subjected to aerobic contact oxidation, and finally it is subjected to advanced treatment. After the combined process runs stably, the indicators such as aniline in the effluent meet the industry's emission standards.

4、 Development Direction of Advanced Treatment Technology for Printing and Dyeing Wastewater

The practical research shows that after the advanced treatment of printing and dyeing wastewater by various processes, the effluent quality is basically in line with the discharge standard and recycling standard, but there are also many problems, such as high operation cost, low recycling rate, etc.

Therefore, in the future development, it is still necessary to actively optimize the advanced treatment technology of printing and dyeing wastewater. The optimized combined process can give full play to the advantages of each combined unit through the combined process. However, there are also problems in the application of the combined process, which needs to be actively optimized. For example, in the treatment of printing and dyeing wastewater, the organic combination of biological ceramsite, ozone decolorization, double-layer filter media filtration, cation exchange resin softening and other process technologies, However, in practice, it was found that the structure of the exchange resin might be destroyed by the residual ozone in the ozone effluent, and the exchange capacity would be gradually lost.

In view of this situation, it is necessary to add the clean water tank to the combined process, and after the complete ozone decomposition, the next process can be carried out. In the future development, it is necessary to deeply study the restriction and destruction of different units in the combined process, take targeted measures, and improve and optimize the combined process. In essence, the purpose of advanced treatment of printing and dyeing wastewater is to actively develop separate reuse technology.

In different processes, different recycled water quality will be produced. If the most stringent water quality requirements are implemented, a lot of resources and costs will be wasted. In view of this situation, enterprises need to fully take into account the requirements of water quality, water volume, etc., and apply the method of separate quality reuse.

1. Strengthen environmental control

In the production practice of the printing and dyeing industry, there will be a large number of dyes, auxiliaries, etc., and there will be a wide variety of them. There will be a large difference in the parameters of dyes and auxiliaries in each process or product production and processing. In order to effectively improve the efficiency of energy conservation and emission reduction in the industry, it is critical to strengthen environmental control. It is not only necessary to track and control the whole production and processing process, but also to effectively treat the subsequent wastewater and pollutants.

In addition, under some traditional technical processes and management modes, the solution preparation accuracy and accuracy are relatively poor, and there is a large consumption of dyes and auxiliaries. The remaining dyes during printing and dyeing will enter the wastewater, so that the content is small, and it is difficult to achieve effective treatment of wastewater and sewage. According to the site conditions and product production requirements, strict precautions should be taken in specific operation links, and a variety of hand punches should be used to encourage the industry.

The enterprise actively introduces automatic batching equipment and automatic operating system to solve the problems of low precision and insufficient accuracy of the traditional liquid mixing method, which can achieve the purpose of energy saving and consumption reduction, and plays a very important role in protecting the ecological environment. It is worth mentioning that it is improving the quality and efficiency of production and processing, saving energy and reducing consumption, and improving the production efficiency of printing and dyeing products.

Concluding remarks

The effluent quality of printing and dyeing wastewater treated by a single method cannot meet the requirements of the new discharge standard, and cannot adapt to the changes in the current printing and dyeing wastewater quality. It is particularly important to conduct in-depth research on the treatment methods and explore the combination of various methods. It is rare to carry out integrated system research on the whole process of printing and dyeing wastewater with different concentrations, which needs further exploration by researchers to adapt to the continuous changes in the quality of printing and dyeing wastewater, Improve the treatment capacity and effect, meet the new emission requirements, and conform to the current environmental management.