Printing and dyeing wastewater is one of the most harmful and difficult to treat industrial wastewaters in China. The main pollutants are dyes, slurries, additives, fiber impurities, oils, acids and bases, and inorganic salts. It is characterized by large amount of wastewater, complex water quality, high concentration of organic matter, difficulty in biodegradation, deep color, fast and unchanging water quality, among which dyes are the most polluted. Even if the concentration of the remaining dye components is low, the light transmittance of the water body is lowered, resulting in destruction of the ecological environment. At present, the domestic treatment of printing and dyeing wastewater is mainly based on biochemical methods, and some are supplemented by chemical methods, but there are widespread shortcomings such as high processing investment cost, high operating cost, poor treatment effect, and difficulty in removing chromaticity. On this basis, there are many studies using physical and chemical treatment methods [1]. Certain COD and chromaticity can be removed by coagulation precipitation [2], chemical oxidation [3], adsorption [4, 5] and membrane technology [6], among which the oxidation method is the most obvious. However, the use of chlorine and ozone has been limited due to problems such as oxidation by-products (such as organic halogens and epoxy compounds) or operating costs. Chlorine dioxide has been widely used as an oxidizing agent with strong oxidizing and rare organic halogenated substances in the oxidation process [7] in the oxidative disinfection of water treatment and the bleaching of papermaking and pulp industry. In recent years, people have studied the new oxidant Cl02 in the treatment of wastewater, and reported the direct treatment of printing and dyeing wastewater with Cl02. In this paper, the status quo, mechanism and development trend of the application of chlorine dioxide in the treatment of printing and dyeing wastewater are reviewed and discussed. The properties of 1 Cl02 and its decolorization mechanism 1.1 Properties of Cl02 Cl02 is a chlorine-like gas that changes from yellowish green to orange-red as the concentration increases. The mass concentration of chlorine dioxide in water was 70 mg/L at 20 cc and atmospheric pressure. The chlorine dioxide gas can be compressed to a liquid density of 2.4 kg/L, a boiling point of 11 o C and a melting point of 59 cc at room temperature. Cl02 is extremely unstable, volatile, and easy to decompose. Generally, C10 is required to be made into a stable aqueous solution. It is used after the acid activator is used at the site of use or C10: the generator is directly added at the site. For drinking water and sewage treatment, chlorine dioxide is used in the form of a solution. 1.2 Decolorization mechanism of Cl02 The treatment of printing and dyeing wastewater by Cl02 is mainly the chromogenic group and the color-assisting group of the oxidative destruction dye, achieving remarkable decolorization effect. Under certain conditions, chlorine dioxide can be combined with DPD (N,N-diethyl-p-phenylenediamine), cresol red (o-cresol), chlorophenol red (dichlorosulfonium), acid indigo (5 , 5 - indigo disulfonate or indigo trisulphonate), lissamine green B (aryl methane dye), rhodamine B (tetraethyl rhodamine) and methylene blue and other color reagents decolorization reaction. When the acid indigo is at pH<4, it can react with the oxidant chlorine dioxide to form a stable compound, blush C8H5NO2. In addition to reacting with dyes such as acid indigo, chlorine dioxide reacts with many direct and reactive dyes to fade the dye. With this property of chlorine dioxide, chlorine dioxide can be used to treat printing and dyeing wastewater. At present, the use of chlorine dioxide to treat printing and dyeing wastewater has made certain progress, especially in the decolorization, and thus has a broad application prospect. 2 Application of chlorine dioxide in the treatment of printing and dyeing wastewater 2.1 Direct treatment of printing and dyeing wastewater Wang Fuxiang et al [8] had tested in Qilin Huayang Printing and Dyeing Co., Ltd., Dachang District, Nanjing. By treating chlorine and dyeing wastewater with chlorine dioxide, the decolorization rate and COD removal rate reached 97.5% and 80.3%, respectively. National emission standards. Lin Dajian [9] used chlorine dioxide as a strong oxidant to oxidatively decompose organic matter in bleaching and dyeing wastewater. The test results show that the removal rate of COD is >78%, the removal rate of chroma is >95%, and the water recycling rate can be Up to 72%. Deng Li et al. [10] used Cl02 to test the decolorization of printing and dyeing wastewater. The results showed that the simulated wastewaters of two reactive dyes (Reactive Brilliant Red X-3B, Reactive Brilliant Red K-2BP) were easily decolorized by C10 oxidation. When the ratio of the concentration of chlorine dioxide to 1:0.24, the decolorization rate of the two reactive dyes can exceed 90%; when the amount of chlorine dioxide is sufficient, the decolorization rate has no relationship with the initial concentration of the dye; The decolorization rate of red X-3B increased little with the change of pH, while the decolorization rate of reactive brilliant red K-2BP increased greatly with the change of pH, and the highest decolorization rate was in the range of pH 7-10; chlorine dioxide and dye The reaction speed is relatively fast, and the reaction can be basically completed in 15 minutes. The temperature has little effect on the reactive brilliant red X-3B, but has a great influence on the decolorization reaction of reactive brilliant red K-2BP. Yu Deshuang [11] proposed a method for the removal of aniline from dye wastewater by chlorine dioxide oxidation according to the productive experimental study of dye wastewater treatment of a fine chemical company. The results show that when the concentration of aniline in the sewage is ≥50mg/L, it is easy to cause active poisoning; when the concentration of aniline in the sewage is ≤50ms/L, the concentration of aniline can be reduced to below 2mg/L by chlorine dioxide oxidation. The removal rate is about 95%. Li Yilin directly treated the printing and dyeing wastewater containing hydrophobic dye (COD 360mg/L, color 256 times) with chlorine dioxide, and filtered by PE precision filter. The effluent water quality was COD64mg/l and color 4 times [12]. A pure cotton dyed cloth factory wastewater containing vulcanization, reduction and disperse dyes, pH=8～12, color=256 times, COD=360 ms/L; 25 g of Cl02 per ton of wastewater is contacted for 30 minutes, using The water effluent is mixed and then filtered through a PE filter. The effluent COD is reduced to 64 mg/L and the chromaticity is 4 times [13]. Zhao Maojun et al. used self-made high-purity chlorine dioxide to carry out oxidative decolorization studies on two commonly used and representative reactive brilliant red K-2G and disperse blue 2BLN dyes, and made temperature, pH value, chlorine dioxide dosage, etc. Conditional tests and experiments with actual printing and dyeing wastewater have achieved good results. At room temperature, t=5~7 minutes, under the condition of alkaline pH, the decolorization rate of single dye solution and mixed dye solution is more than 90%, and the decolorization of actual printing and dyeing wastewater is also about 90%. Various factors such as pH value, temperature and amount of Cl02 have certain effects on the decolorization rate: the higher the pH value, the higher the decolorization rate of the dye. The optimum amount of Cl02 is present, and the optimum molar ratios of reactive brilliant red K-2G and disperse blue 2BLN dye are about 40 and 20, respectively. The Cl02 consumption increases as the initial concentration of the dye increases (when the decolorization rate is the same) [14]. Zhang Chunhui et al. [15] chlorine dioxide was used to study the decolorization of dyes and printing and dyeing wastewater. The results showed that chlorine dioxide has a good decolorization effect. When the raw water COD is 1592 ms/L and the color is 781 times, the wastewater is 781 times. Without adjusting the pH (raw water pH=7.6), after treatment with chlorine dioxide at a dose of 75 mg/L for 4 h, the COD removal rate was 68.4%, the chroma removal rate was over 94%, and the water sample was almost colorless. The test also found that the pH value has a great influence on the oxidative decolorization of Cl02, and has a good decolorization effect under acidic conditions. Printing and dyeing wastewater is mostly alkaline, and it is unfavorable to directly decolorize with Cl02. It is necessary to adjust the pH of the wastewater first. This is an unfavorable factor that must be considered when using chlorine dioxide for decolorization. 2.2 Used in conjunction with other processes The printing and dyeing wastewater contains not only dyes but also a large amount of refractory substances such as dyeing auxiliaries and detergents. As an oxidant, Cl02 can effectively oxidize chromophores in dye molecules, and the decolorization effect is remarkable. However, the removal effects of dyeing auxiliaries such as starch, sodium alginate, polyvinyl alcohol and carboxymethyl cellulose in wastewater are effective. Very poor. Therefore, the Cl02 oxidation method usually needs to be combined with coagulation, air flotation, adsorption, filtration and biochemical methods to achieve the treatment standard. Jiangsu Tianlun Dyeing and Weaving Industrial Co., Ltd. and Jingjiang No.3 Textile Factory _l use the coagulation-chlorine dioxide combination method to treat printing and dyeing wastewater. The removal rate is 95%, COD is 82.5-83.7%, BOD is 96%, SS is 67.2 ~ 75.5%, S is 86.5 ~ 98.3%, it can be seen that the effluent water color removal rate is high, no color change phenomenon, COD and other indicators can reach the national GB8978-88 discharge standard. The whole process equipment is simple, the power consumption is small, the operation and management are convenient, the engineering cost is low, and the effect is fast, which is worth promoting. He Qihuan [17] conducted a chlorine dioxide catalytic oxidation experiment on the wastewater prepared from micro-electrolytic pretreatment of acid red dye. The results showed that when the wastewater COD=3400ms/L, pH: 4, the oxidation reaction time is 45 minutes, C10 The addition amount is 750mg/L. Under the action of the catalyst, the average removal rate of COD is about 88%, and the average removal rate of COD is only about 28%. Wang Jiusi [18] and other experiments using C10 oxidation-batch activated sludge treatment of printing and dyeing wastewater showed that the oxidation and decolorization effect of Cl02 was obvious. When the amount of Cl02 was 50ms/L, the decolorization rate was over 85%, and the COD removal rate was More than 75%, and both increase with the increase in the amount of Cl02. The oxidative decolorization rate of Cl02 is little affected by pH and can be fully adapted to the processing requirements in a wide pH range. After the dye wastewater is treated by Cl02 oxidation and intermittent activated sludge treatment, the effluent quality meets the first-class standard in GB8978-88 Integrated Wastewater Discharge Standard. 3 Conclusion In summary, the use of Cl02 to treat printing and dyeing wastewater has the advantages of simple equipment, low investment, low energy consumption, convenient operation and management, good effluent quality, good social and environmental benefits, and broad application prospects. Shanghai Chuangsai Technology has excellent performance, interleukin cytokines, fetal bovine serum, electrophoresis equipment scientific instruments, raw material drug standards, chemical reagents, cell culture consumables, Shanghai Chuangsai, mass products special promotions, welcome to inquire! Porcelain Embossed Dinner Set,Porcelain Soup Bowl,Porcelain Embossed Dinnerware Set,Pad Printing Design Dinner Plates Henan WonkingChina I/E Co., Ltd. , https://www.wshousewares.com