Removal of chroma in printing and dyeing wastewater

Printing and dyeing industry wastewater has a large chroma, which will adversely affect the drainage of printing and dyeing wastewater, and these colored pollutants are also a toxic substance. In the engineering design of printing and dyeing wastewater, it is not only necessary to consider the chromaticity of the standard discharge, but also the removal rate of pollutants such as chromaticity and COD. Our company believes that the decolorization of printing and dyeing wastewater treatment is best carried out by biochemical treatment.

Biological decolorization is the use of microbial enzymes to oxidize or reduce dye molecules, destroying their unsaturated bonds and chromophores. The decolorizing microorganism first adsorbs and enriches the dye molecules, followed by biodegradation. Dye molecules are finally degraded into simple inorganic substances or converted into various nutrients and protoplasts through a series of activities such as oxidation, reduction, hydrolysis, and chemical reaction.

Subtle structural changes of dye molecules will affect the decolorization rate, and different microorganisms have different dye removal rates for different structures. The dye concentration also has a certain influence on the decolorization rate. High concentration dyes (the dye itself has strong biological toxicity) will inhibit Microbial activity affects the decolorization effect.

The aerobic process is a common treatment process, but due to the strong biodegradability of the dye molecules, the BOD5/COD ratio decreases during the treatment process (the biodegradability is deteriorated), resulting in the coloration and COD removal rate of the common aerobic process. Not high (60 to 70%). By adding iron salt, activated carbon and other adsorbing substances to the aeration tank, the residence time of the refractory substance in the system can be prolonged, the activated sludge concentration of the aeration tank can be increased, the sludge load can be reduced, and the decolorization rate of the system can be improved. COD removal rate. The anaerobic (hydrolysis acidification)-aerobic treatment process developed in recent years can make up for the deficiency of the aerobic process to a certain extent. However, the biochemical treatment process alone cannot meet the requirements of chroma and COD stability.

Pre-treatment and subsequent treatment of wastewater for the production and different water quality of the enterprise can ensure that the color and other pollutants can reach the standard discharge.

The woven fabric printing and dyeing process usually includes desizing wastewater, scouring wastewater, dyeing wastewater, and the like. This kind of wastewater has high alkalinity, high chroma, high COD, high water temperature, and a wide variety of dyes. Sometimes, sulfur dyes are used in the production process, which will contain a certain amount of sulfide. If PVA is used as the slurry, mix. The wastewater will contain a certain amount of PVA with very poor biodegradability. The wastewater is simply anaerobic-aerobic or delayed aeration, and the effluent COD and chromaticity are difficult to reach the standard. When the system effluent is added to strengthen the oxidant, the sulfide will be converted into sulfur and the effluent will be in the form of a thin rice soup. Milky white, the color is still difficult to reach the standard. In the treatment of such wastewater, if the physicochemical treatment facility is added before the biochemical treatment, the decolorizing agent mainly composed of ferrous sulfate and polyaluminum chloride can be used to remove about 80% of the chromaticity and more than 95% of the sulfide. And about 40% of COD, which also removes some of the refractory macromolecular dyes. If combined with well-designed biochemical processes, the COD and color of the wastewater can reach the standard.

The dyeing wastewater of denim yarn has high chroma and high COD. This kind of wastewater uses a large amount of sulphur dyes in the printing and dyeing process. Therefore, the wastewater contains a large amount of sulfides, often as high as 200-1000 mg/L, and the chroma is as high as 2000-3000 times. . This kind of wastewater must also be pretreated by physical and chemical addition, and then biochemically treated to achieve stable discharge.

The denim garment rinsing wastewater contains additives such as dyes, slurries and surfactants. This type of wastewater has a large amount of water, and its concentration and chroma are low. If physicochemical treatment is used alone, the effluent COD is only between 100 and 200 mg/L, and the chromaticity can meet the discharge requirements, but the sludge volume is greatly increased. The cost of treatment is high and it is easy to cause “secondary pollution”. Therefore, biochemical treatment should also be considered.

Knitted cloth (yarn) printing and dyeing wastewater and sweater printing and dyeing wastewater, using cationic dyes, reactive dyes, disperse dyes, etc. Decolorization of this kind of wastewater in the first-level physical and chemical treatment, mostly using ferrous sulfate-based decolorizing agent, coagulant often uses slaked lime powder, but the addition of lime will lead to pipeline fouling, resulting in system maintenance workload Increase. In addition, once combined with the oxygen in the air, the effluent will oxidize the divalent iron ions to ferric ions, and the water body will appear turbid yellow brown iron rust.

Knitted fabric (yarn) printing and dyeing wastewater and sweater printing and dyeing wastewater can generally be directly subjected to anaerobic-aerobic-based biochemical treatment, but sometimes the phenomenon of increased chroma in the aerobic system, indicating that the biochemical system is operating well. However, in addition to the strong oxidant, the decoloring agent removal effect is not satisfactory, and the contact reaction time of the strong oxidant and the wastewater should be controlled within 30 to 60 minutes. The decolorization of such wastewater should also take into account the impact of water quality fluctuations. When receiving a batch of orders for vulcanization printing, enterprises often discharge sulphide-containing wastewater within one week or 10 days. Due to microbial suitability and other reasons, Sulfide in the discharged wastewater will strongly inhibit the activity of the microorganisms, resulting in different levels of COD and chromaticity of the effluent. This part of the wastewater should be subjected to physicochemical pretreatment before biochemical treatment.

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