Summary of decolorization treatment technology for printing and dyeing wastewater at home and abroad
Textile printing and dyeing wastewater , large amount of water, high chroma, complex composition, wastewater containing dyes, slurries, auxiliaries, acids, alkalis, fiber impurities and inorganic salts, amine compounds in the dye structure and copper, chromium, zinc, Heavy metal elements such as arsenic have greater toxicity. At present, 10-20% of dyes in the dyeing process are discharged into the wastewater, which seriously pollutes the environment. With the development of the dye industry and the advancement of printing and dyeing processing technology, the stability of the dye structure is greatly improved, which makes the decolorization treatment more difficult. At present , the decolorization problem of printing and dyeing wastewater has become a major problem in the domestic and international wastewater treatment . Most printing and dyeing factories use a combination of chemical treatment and biochemical treatment . Biochemical treatment uses microbial methods to degrade dye molecules and organic matter. However, the biochemical treatment process has low degradation rate of harmful molecules, large equipment investment, and high operating cost. Therefore, choose a simple one. The cost-effective treatment method has become the research focus of dyeing wastewater. In addition to biochemical methods, other physical chemical or chemical decolorization methods such as adsorption, redox, ion exchange, membrane, and coagulation have been reported in many applications and applications, but the treatment results are not very satisfactory. Summary of dyeing wastewater treatment process at home and abroad Adsorption decolorization One of the main advantages of adsorption decolorization is that the dye can be removed from the water by adsorption, and the adsorption process retains the structure of the dye. As an excellent adsorbent, activated carbon has been widely used in water treatment. It is still the best adsorbent for colored printing and dyeing wastewater. Activated carbon is selective for dyes. The decolorization performance is followed by basic dyes, direct dyes, acid dyes and Sulfur dyes. Activated carbon is expensive and difficult to regenerate, so it is generally only used in the treatment or deep treatment of printing wastewater with low concentration. Molecular sieves, activated aluminum, granular activated carbon (GAC), diatomaceous earth and sawdust can be used as adsorbents for disperse dye 1260, but activated carbon has the best effect in removing chroma and COD. The treatment of printing and dyeing wastewater with montmorillonite as adsorbent has a decolorization rate and COD removal rate of over 90% and 96.9%, respectively. The biggest problem with adsorbents is that it is difficult to achieve on-site regeneration. S. Karcher [4] developed a new renewable adsorbent, CUCURBITURIL, which is a cyclic polycondensate formed by polycondensation of glycoluril and formaldehyde. A large number of experiments have shown that the substance is non-toxic, and when the calcium ion concentration is 1-100 mmol/L, and the total concentration of the salt in the solution is less than 100-1000 mmol/L, a high adsorption amount can be obtained, and the residual color is very high. low. Redox decolorization The conjugated system or chromophore group which destroys the dye by means of redox is an effective method for dyeing and decolorizing. In addition to the conventional chlorine oxidation method, research at home and abroad mainly focuses on ozone oxidation, hydrogen peroxide oxidation, electrolytic oxidation and photooxidation. Ozone is a good decolorizing oxidant. For dyes containing water-soluble dyes such as active, direct, cationic and acidic dyes, the decolorization rate is high. It also has good decolorization effect on disperse dyes but other reduction and vulcanization in the wastewater in suspension. And paint, the decolorization effect is poor. The results of Matsui et al. show that azo dyes are more susceptible to oxidation by ozone. The amount of ozone is related to the number of azo groups. For example, for 0.1 mol/l direct red 2S and direct black 2S, the ozone demand is 80 and 130 mg/l, respectively. Ozone oxidation can also be combined with other processing techniques. If FeSO4, Fe2(SO4)3 and FeCl3 are coagulated and then treated with ozone, the decolorization effect can be improved. Ozone treatment can increase the decolorization rate of direct and acid dyes by 25-40% compared with ozone treatment. The dye is increased by 10%. Ozone plus ultraviolet radiation or simultaneous ionizing radiation can also increase oxidation efficiency. Ozone oxidation has wide adaptability to dye varieties and high decolorization efficiency. At the same time , the reduction products of O3 in wastewater and excess O3 can be rapidly decomposed into O2 in solution and air, which will not cause secondary pollution to the environment. Therefore, O3 decolorization technology has certain industrial application prospects. At present, the main deficiency of ozone oxidation is that the operating cost is relatively high. Fenton reagent is a strong oxidizing agent which is a mixture of H2O2 and FeSO4 in a certain ratio. In addition to oxidation, Fenton's reagent also has a coagulation effect in the process of treating wastewater, so the decolorization efficiency is high. In recent years, it has been widely used in the decolorization treatment of dyes and wastewater. The conventional H2O2 oxidation is currently in the form of Fenton reagent. In order to fully understand the decolorization ability of Fenton reagent for various dyes, Kuo, W, and G selected a representative compound covering 90% of commonly used dye varieties for simulation study. The results show that under acidic conditions (pH<3), the average decolorization rate can reach 97%, and the COD removal rate can reach 90%. In the actual application process, the inorganic acid can be used to adjust the pH of the wastewater to 2~5, and then treated with H2O2/Fe2+. After being treated with Fenton reagent, the pH value can be adjusted and added to further enhance the Fe3+ coagulation effect. A small amount of polymer coagulant. Advanced oxidation decolorization is considered a promising approach. The so-called advanced oxidation methods such as UV+H2O2 and UV+O3, because of the generation of hydroxyl radicals in the oxidation process, their strong oxidizing properties decolorize the dye wastewater. It has been found that it is very effective for the decolorization of azo dyes. In the actual production, it can improve the decolorization effect with certain chemical adjuvants, and the degradation products produced by the UV+H2O2 method for treating azo-type reactive dyes are completely harmless to the environment. Recent studies have found that dichlorotriazinyl azo reactive dyes also have good effects by UV+H2O2 decolorization. Therefore, decolorization by advanced oxidation can be used as a pretreatment for biological treatment. A serious shortcoming of the advanced oxidation process is the high processing cost, which limits its widespread use. Coagulation decolorization treatment technology The coagulation decolorization effect of the water-soluble dye of the dye is closely related to its existence in water, and the existence state of the dye in water depends on its molecular structure and physicochemical properties. Dyes have three states of existence in printing and dyeing wastewater: dissolved, colloidal and suspended. The weak acid dyes are generally monoazo or disazo. The structure is relatively complicated. The molecule contains hydrophilic groups such as -SO3H and -OH, and the solubility is medium. It exists in the aqueous solution in a state close to the colloid at room temperature, and is easily mixed. It is removed by coagulation and has a good decolorizing effect in a wide range of pH 3-10. The basic skeleton of the molecular structure of the reducing dye is a polycyclic aromatic compound having a relatively large molecular weight, which contains -C=O and -NH- groups, and has a hydrophobic aromatic ring and a small number of hydrophilic groups. The disperse dye often has an azo and an anthracene skeleton, and the molecule contains a polar group such as -O- or -NH- and no hydrophilic group such as -SO3H or -OH. Both of these types are nonionic hydrophobic dyes, which have very low solubility in water and poor stability. Coagulants are easily agglomerated and removed after being added, and the amount of coagulant required is small. Direct dyes generally belong to the structure of bisazo, trisazo or diphenylhexene . The hydrophilic groups such as -SO3H, -OH and -COOH are high in content, good in water solubility and high in solubility. The reactive dyes are monoazo type, hydrazine type, phthalocyanine type, etc. The dye precursor contains a large number of hydrophilic groups such as -SO3H, -OH, -COOH, and has good solubility in water. The above two types of dyes are mostly in a state close to a true solution, and even if the dosage of the coagulant is large, the decolorization rate is low. Mens Leather Boot,Men'S Heavy Leather Boot,Men'S Snow Leather Boot,Men'S Dress Casual Boot Guangdong XDDD Footwear Crop. Ltd , https://www.xdshoe.com