Chlorine dioxide, as an oxidizing agent with strong oxidizing and little organic halogenated substances in the oxidation process, has been widely used in the oxidative disinfection of water treatment and the bleaching of papermaking and pulp industry. In recent years, people have studied the new oxidant chlorine dioxide in the treatment of wastewater, and reported the use of chlorine dioxide to directly treat printing and dyeing wastewater.
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. Certain COD and chromaticity can be removed by coagulation sedimentation, chemical oxidation, adsorption and membrane technology, among which the oxidation method is 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.
1. The nature of chlorine dioxide and its decolorization mechanism
1.1 The nature of chlorine dioxide
Chlorine dioxide is a chlorine-like gas that changes from yellow-green to orange-red as the concentration increases. The mass concentration of chlorine dioxide in water is 70 mg/L at a standard atmospheric pressure of 20 °C. The chlorine dioxide gas can be compressed to a liquid density of 2.4 kg/L and a boiling point of 11 ° C at room temperature. Chlorine dioxide is extremely unstable, volatile, and easy to decompose. Generally, chlorine dioxide is firstly made into a stable aqueous solution. It is used after being used with an acidic activator at the site of use or directly at the site of a chlorine dioxide generator.
For drinking water and sewage treatment, chlorine dioxide is used in the form of a solution.
1.2 Decolorization mechanism of chlorine dioxide
Chlorine dioxide treatment of printing and dyeing wastewater is mainly caused by oxidative destruction of the chromophoric group and the color-assisting group of the dye, achieving a 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. Acidic indigo can form a stable compound, blush C8H5NO2, when the pH is <4. 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
He has been tested in Qilin Huayang Printing and Dyeing Co., Ltd., Dachang District, Nanjing. Through the treatment of printing and dyeing wastewater with chlorine dioxide, the decolorization rate and COD removal rate reached 97.5% and 80.3%, respectively. The treated wastewater index is in full compliance with national emission standards.
Oxidative decomposition of organic matter in bleaching and dyeing wastewater by using chlorine dioxide as a strong oxidant shows that the removal rate of COD is >78%, the removal rate of chroma is >95%, and the water recycling rate can reach 72%.
The test results of decolorization of printing and dyeing wastewater by using chlorine dioxide show that the simulated wastewater of two reactive dyes (Reactive Brilliant Red X-3B, Reactive Brilliant Red K-2BP) is easily oxidized by chlorine dioxide, when dye and dioxide When the concentration ratio of chlorine is 1:0.24, the decolorization rate of both reactive dyes can exceed 90%; when the amount of chlorine dioxide is sufficient, the decolorization rate has no relationship with the initial concentration of dye; active brilliant red X- The decolorization rate of 3B increases little with the change of pH, while the decolorization rate of reactive brilliant red K-2BP increases greatly with the change of pH. The decolorization rate of pH is the highest in the range of 7-10; between chlorine dioxide and dye The reaction rate is faster, 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.
According to the productive experimental study of dye wastewater treatment of a fine chemical company, a method for removing aniline from dye wastewater by chlorine dioxide oxidation was proposed. 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%.
The printing and dyeing wastewater containing hydrophobic dye (COD360mg/L, color 256 times) was directly oxidized by chlorine dioxide, and filtered by PE precision filter. The effluent water quality was COD64mg/L and the color was 4 times. A pure cotton yarn-dyed cloth wastewater containing vulcanization, reduction and disperse dyes, pH=8～12, color=256 times, COD=360ms/L; 25g chlorine dioxide is added to each ton of wastewater for 30 minutes. It is mixed with water effluent and then precisely filtered by PE filter. The effluent COD is reduced to 64mg/L and the chromaticity is 4 times.
Oxidative decolorization studies were carried out on two commonly used and representative reactive brilliant red K-2G and disperse blue 2BLN dyes using self-made high-purity chlorine dioxide. Temperature, pH, chlorine dioxide dosage and other conditions were tested and used. The actual printing and dyeing wastewater was tested and 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 chlorine dioxide dosage have certain effects on the decolorization rate: the higher the pH value, the higher the decolorization rate of the dye.
The optimum amount of chlorine dioxide is present, and the optimum molar ratios to Reactive Brilliant Red K-2G and Disperse Blue 2BLN dye are about 40 and 20, respectively. The chlorine dioxide consumption increases as the initial concentration of the dye increases (when the decolorization rate is the same).
The decolorization of dyes and printing wastewater was studied by using chlorine dioxide. The results showed that chlorine dioxide has good decolorization effect. When the raw water COD is 1592ms/L and the color is 781 times, the wastewater is not adjusted. Under (raw water pH=7.6), after treatment with chlorine dioxide at 75mg/L for 4h, 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 chlorine dioxide, and has a good decolorization effect under acidic conditions. Printing and dyeing wastewater is mostly alkaline, and it is unfavorable to directly decolorize with chlorine dioxide. It is necessary to adjust the pH of the wastewater first. This is a disadvantage that must be considered when using chlorine dioxide for decolorization.
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3, one yuan chlorine dioxide disinfection powder
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