Textile wastewater is mainly wastewater containing natural impurities, fats, starch and other organic substances generated during the process of raw material cooking, rinsing, bleaching, sizing, etc. Printing and dyeing wastewater is generated in multiple processes such as washing, dyeing, printing, sizing, etc., and contains a large amount of organic substances such as dyes, starch, cellulose, lignin, detergents, as well as inorganic substances such as alkali, sulfide, and various salts, which are highly polluting.
Characteristics of printing and dyeing wastewater
The textile printing and dyeing industry is a major discharger of industrial wastewater. The wastewater mainly contains dirt, grease, salts on textile fibers, and various slurries, dyes, surfactants, additives, acids and alkalis added during the processing process.
The characteristics of wastewater are high organic concentration, complex composition, deep and variable chromaticity, large pH changes, large changes in water volume and water quality, and it is difficult to treat industrial wastewater. With the development of chemical fiber fabrics, the rise of imitation silk and the improvement of post-printing and dyeing finishing requirements, a large amount of refractory organic matter such as PVA slurry, rayon alkaline hydrolyzate, new dyes, and auxiliaries have entered the textile printing and dyeing wastewater, posing a serious challenge to the traditional wastewater treatment process. The COD concentration has also increased from hundreds of milligrams per liter to 3000-5000 mg/l.
The slurry and dyeing wastewater has high chroma and high COD, especially the printing and dyeing processes such as mercerized blue, mercerized black, extra dark blue, and extra dark black developed according to the foreign market. This type of printing and dyeing uses a large amount of sulfur dyes and printing and dyeing auxiliaries such as sodium sulfide. Therefore, the wastewater contains a large amount of sulfide. This type of wastewater must be pre-treated with drugs and then subjected to serial treatment to stably meet the discharge standards. The bleaching and dyeing wastewater contains dyes, slurries, surfactants and other auxiliaries. The amount of this type of wastewater is large, and the concentration and chromaticity are both low. If physical and chemical treatment is used alone, the effluent is also between 100 and 200 mg/l, and the chromaticity can meet the discharge requirements, but the amount of pollution is greatly increased, the cost of sludge treatment is high, and it is easy to cause secondary pollution. Under the condition of strict environmental protection requirements, the biochemical treatment system should be fully considered. Conventional enhanced biological treatment processes can meet the treatment requirements.
Chemical treatment method
Coagulation method
There are mainly mixed sedimentation method and mixed flotation method. The coagulants used are mostly aluminum salts or iron salts. Among them, basic aluminum chloride (PAC) has better bridging adsorption performance, and the price of ferrous sulfate is the lowest. The number of people using polymer coagulants abroad is increasing, and there is a trend of replacing inorganic coagulants, but in China, due to price reasons, the use of polymer coagulants is still rare. It is reported that weak anionic polymer coagulants have the widest range of use. If used in combination with aluminum sulfate, they can play a better effect. The main advantages of the mixed 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 difficulty in dehydration, and poor treatment effect on hydrophilic dyes.
Oxidation method
Ozone oxidation method is widely used abroad. Zima S.V. et al. summarized the mathematical model of ozone decolorization of printing and dyeing wastewater. Studies have shown that when the ozone dosage is 0.886gO3/g dye, the decolorization rate of light brown dye wastewater reaches 80%; the study also found that the amount of ozone required for continuous operation is higher than that required for intermittent operation, and the installation of partitions in the reactor can reduce the amount of ozone by 16.7%. Therefore, when using ozone oxidation decolorization, it is advisable to design an intermittent reactor and consider installing partitions in it. Ozone oxidation method can achieve good decolorization effect for most dyes, but the decolorization effect is poor for water-insoluble dyes such as sulfide, reduction, and coatings. Judging from the operating experience and results at home and abroad, this method has good decolorization effect, but it consumes a lot of electricity, and it is difficult to promote and apply it on a large scale. The photooxidation method has a high decolorization efficiency for treating printing and dyeing wastewater, but the equipment investment and power consumption need to be further reduced.
Electrolysis method
Electrolysis has a good treatment effect on the treatment of printing and dyeing wastewater containing acid dyes, with a decolorization rate of 50% to 70%, but the treatment effect on wastewater with dark color and high CODcr is poor. Studies on the electrochemical properties of dyes show that the order of CODcr removal rate of various dyes during electrolytic treatment is: sulphur dyes, reducing dyes> acid dyes, active dyes> neutral dyes, direct dyes> cationic dyes, and this method is being promoted and applied.
What indicators should be tested for printing and dyeing wastewater
1. COD detection
COD is the abbreviation of chemical oxygen demand in printing and dyeing wastewater, which reflects the amount of chemical oxygen required for the oxidation and decomposition of organic and inorganic matter in wastewater. COD detection can reflect the content of organic matter in wastewater, which is of great significance for detecting the content of organic matter in printing and dyeing wastewater.
2. BOD detection
BOD is the abbreviation of biochemical oxygen demand, which reflects the amount of oxygen required when organic matter in wastewater is decomposed by microorganisms. BOD detection can reflect the content of organic matter in printing and dyeing wastewater that can be degraded by microorganisms, and more accurately characterize the content of organic matter in wastewater.
3. Chroma detection
The color of printing and dyeing wastewater has a certain stimulation to the human eye. Chroma detection can reflect the level of chroma in wastewater and have a certain objective description of the degree of pollution in printing and dyeing wastewater.
4. pH value detection
pH value is an important indicator to characterize the acidity and alkalinity of wastewater. For biological treatment, pH value has a greater impact. Generally speaking, the pH value should be controlled between 6.5-8.5. Too high or too low will affect the growth and metabolic activities of organisms.
5. Ammonia nitrogen detection
Ammonia nitrogen is a common indicator in printing and dyeing wastewater, and it is also one of the important organic nitrogen indicators. It is the product of the decomposition of organic nitrogen and inorganic nitrogen into ammonia in printing and dyeing wastewater. Excessive ammonia nitrogen will lead to the accumulation of nitrogen in water, which is easy to cause eutrophication of water bodies.
6. Total phosphorus detection
Total phosphorus is an important nutrient salt in printing and dyeing wastewater. Excessive total phosphorus will lead to eutrophication of water bodies and affect the health of water bodies. The total phosphorus in printing and dyeing wastewater mainly comes from dyes, auxiliaries and other chemicals used in the printing and dyeing process.
In summary, the monitoring indicators of printing and dyeing wastewater mainly cover COD, BOD, chromaticity, pH value, ammonia nitrogen, total phosphorus and other aspects. Only by comprehensively testing these indicators and properly treating them can the pollution of printing and dyeing wastewater be effectively controlled.
Lianhua is a manufacturer with 40 years of experience in producing water quality testing instruments. It specializes in providing laboratory COD, ammonia nitrogen, total phosphorus, total nitrogen, BOD, heavy metals, inorganic substances and other testing instruments. The instruments can quickly produce results, are simple to operate, and have accurate results. They are widely used in various companies with wastewater discharge.
Post time: Oct-24-2024
