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Printing and dyeing wastewater treatment method

by:BOQU     2023-03-30
Printing and dyeing wastewater is wastewater discharged from printing and dyeing factories that mainly process cotton, hemp, chemical fibers and their blended products. Printing and dyeing wastewater has a large amount of water, 100-200 tons of water is consumed per ton of textile printing and dyeing, of which 80-90% becomes wastewater. Textile printing and dyeing wastewater has the characteristics of large water volume, high content of organic pollutants, high alkalinity, and large changes in water quality. It is one of the most difficult industrial wastewater to treat. Wastewater contains dyes, pastes, additives, oils, acids and bases, fiber impurities, sand substances, inorganic salts, etc. 1. Classification of printing and dyeing wastewater 1. Desizing wastewater: small amount of water, high concentration of pollutants, mainly containing pulp and its decomposition products, lint, acid, starch alkali and enzyme pollutants, high turbidity; wastewater is alkaline , the pH value is around 12. When the starch slurry is used, both BOD and COD are high, and the biodegradability is good; when the synthetic slurry is used, the COD is very high, and the BOD is less than 5mg/L, and the water biodegradability is poor. 2. Smelting wastewater: large amount of water, high concentration of pollutants, mainly containing cellulose, fruit acid, wax, grease, alkali, surfactant, nitrogenous compounds, etc. The wastewater has strong alkalinity, high water temperature, brown color, high COD and BOD, up to thousands of milligrams per liter. The pollution of chemical fiber cooking wastewater is relatively light. 3. Bleaching wastewater: large amount of water, light pollution, mainly contains residual bleaching agent, a small amount of acetic acid, oxalic acid, sodium thiosulfate, etc. 4. Mercerizing wastewater: high alkali content, NaOH content is 3%-5%, most printing and dyeing factories recover NaOH through evaporation and concentration, so mercerizing wastewater is generally rarely discharged, and the wastewater discharged after repeated use of the process is still strong alkali Sex, BOD, COD, SS are higher. 5. Dyeing wastewater: the water quality is variable, and sometimes contains toxic substances when using various dyes (alkali sulfide, tartar, aniline, copper sulfate, phenol, etc.), alkaline, and sometimes the pH is above 10 (using sulfur and vat dyes) ), containing organic dyes, surfactants, etc. High chroma, less SS, higher COD than BOD, and poor biodegradability. 6. Printing wastewater: containing slurry, high BOD and COD. 7. Wastewater from the finishing process: mainly contains lint, resin, formaldehyde, oil and slurry, with little water. 8. Alkali reduction wastewater: It is produced by the alkali reduction process of polyester imitation silk, mainly containing polyester hydrolyzate terephthalic acid, ethylene glycol, etc., of which the content of terephthalic acid is as high as 75%. Alkali reduction wastewater not only has a high pH value (generally>12), and the concentration of organic matter is high. The CODcr in the wastewater discharged from the alkali reduction process can be as high as 90,000 mg/L. The high-molecular organic matter and some dyes are difficult to be biodegraded. This kind of wastewater is a high-concentration refractory organic wastewater. Second, printing and dyeing wastewater treatment methods 1. Adsorption method The most widely used physical treatment method is the adsorption method. This method is to mix the powder or particles of porous substances such as activated carbon and clay with the wastewater, or let the wastewater pass through the particles. A filter bed is composed of a method in which pollutants in wastewater are adsorbed on the surface of porous materials or removed by filtration. The adsorption rate, BOD removal rate and COD removal rate of activated carbon are 93%, 92% and 63% respectively. 2. Coagulation methods mainly include coagulation sedimentation method and coagulation air flotation method. Most of the coagulants used are aluminum salts or iron salts. Among them, basic aluminum chloride (PAC) has better bridging adsorption performance. good. The main advantages of the coagulation method are simple process flow, convenient operation and management, low equipment investment, small footprint, and high decolorization efficiency for hydrophobic dyes; the disadvantages are high operating costs, large amount of sludge, and difficult dehydration. Water-based dyes are less effective. 3. Oxidation method Ozone oxidation method can obtain good decolorization effect on most dyes, but the decolorization effect on vulcanization, reduction, paint and other water-insoluble dyes is poor. From domestic and foreign operating experience and results, this method has a good decolorization effect, but consumes a lot of power, and it is difficult to popularize and apply it on a large scale. Oxidation treatment of printing and dyeing wastewater has a high decolorization efficiency, but equipment investment and power consumption need to be further reduced. 4. Electrolysis Electrolysis has a good treatment effect on the treatment of printing and dyeing wastewater containing acid dyes, and the decolorization rate is 50% to 70%, but the treatment effect on wastewater with deep color and high CODCr is poor. 5. Biological methods The surface accelerated aeration and contact oxidation methods account for the majority of the biological treatment methods for printing and dyeing wastewater in my country. In addition, the blast aerated activated sludge method, the jet aerated activated sludge method, and the biological turntable are also applied, and the biological fluidized bed is still in the experimental application stage. Since the biological removal rate of chroma is not high, generally around 50%, when the effluent chroma is required to be high, physical or chemical treatment is required.
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