Mercerizing is the treatment of fabrics in a concentrated solution of sodium hydroxide to increase the tensile strength of the fibers, increase the surface gloss of the fibers, reduce the potential shrinkage of the fabric and increase the affinity for the dye. The mercerized wastewater is generally recovered after evaporation and concentrated, and a small amount of mercerized wastewater discharged from the end is more alkaline.

In order to deal with the problem of printing and dyeing mercerized wastewater, this article focuses on the related situation of printing and dyeing wastewater and its treatment methods.

First, printing and dyeing wastewater quality and water volume 1: different products discharged wastewater quality Dyeing products due to different raw fiber, product type and production process, the use of dyes, additives and types of different, different processing methods, different times of rinsing, Therefore, the quality of the discharged wastewater is also different. In addition, due to the different proportions of different chemical fibers in various types of products, the types of dyes and auxiliaries used are constantly changing, so the water content of each pollutant in the discharged wastewater is also not the same.

In the cotton blended textile products, due to the increase of chemical fibers (mainly polyester) (generally 65%), the warp yarns are sizing using a mixture of modified starch and polyvinyl alcohol. In the desizing wastewater produced by the pre-treatment process of printing and dyeing, due to the presence of a certain amount of polyethanol, the biodegradable substances are increased in the wastewater, and the biodegradability of the wastewater is reduced. Therefore, cotton printing and dyeing wastewater is one of the more difficult biodegradable industrial wastewater.

In wool dyeing products, due to the large proportion of natural fibers, the proportion of chemical fibers is relatively small, and there is no need for sizing in the weaving process. Therefore, the quality of waste water produced during the processing of wool blended textile dyeing and finishing products is relatively stable. The biodegradability is better than printing and dyeing wastewater discharged from cotton spinning products. The hair washing wastewater has good biodegradability, and generally the biological treatment method should be adopted after the extraction of lanolin.

The printing and dyeing wastewater discharged during the processing of silk printing and dyeing products belongs to medium and low concentration organic wastewater, and has good biodegradability.

The waste water produced in the alkali reduction process of chemical fiber artificial silk products contains a considerable amount of terephthalic acid and ethylene glycol. Overall, the biodegradability of waste water is poor, but after mixing with printing and dyeing wastewater, the water quality is slightly improved. .

2: Wastewater Amount of printing and dyeing wastewater discharge is about 60% to 80% of the whole plant water consumption. The amount of wastewater varies depending on the type of plant, production process, machinery and equipment, and the variety of processed products. According to domestic and foreign data estimates, the water consumption is approximately 1 to 1.2 m3 per processed cotton fabric.

Second, the characteristics and hazards of printing and dyeing wastewater 1, the characteristics of wastewater (1) large amount of water.

(2) High concentration.

(3) The water quality fluctuates greatly.

(4) Contamination with organic matters.

(5) It is difficult to handle.

(6) Some wastewater contains poisonous and harmful substances.

2. Dangers of Wastewater Printing and dyeing wastewater contains a large amount of organic pollutants. Discharging oxygen will be consumed when discharged into water bodies, destroying ecological balance of water and endangering the survival of fish and other aquatic organisms. Submerged organic matter will generate harmful gases such as hydrogen peroxide due to anaerobic decomposition and deteriorate the environment.

The deep color of printing and dyeing wastewater seriously affects the appearance of receiving water bodies. The main cause of colouring in water bodies is dyes. In textile printing and dyeing, 10% to 20% of the dye is discharged as waste. The color of printing and dyeing wastewater is particularly serious, and it is difficult to remove it by general biochemical methods. Colored water also affects the transmission of sunlight and is not conducive to the growth of aquatic organisms.

Most of the printing and dyeing wastewater is alkaline, and entering the farmland will make the land salinize; the sulfate of the dyeing wastewater can be converted into sulfides under the reducing conditions of the soil to produce hydrogen sulfide.

Third, the basic methods of printing and dyeing wastewater treatment Printing and dyeing wastewater is organic pollution-based, complex organic wastewater, the main object of treatment is BOD5, not easily biodegradable or slow biodegradation of organic matter, alkalinity, dye color and a small amount of toxic substance. Although the biodegradability of printing and dyeing wastewater is generally poor, it is still a biodegradable organic wastewater except for some special printing and dyeing wastewater (such as dyeing of purified fiber fabrics). The treatment method is mainly based on the biological treatment method, and it needs to be supplemented with the necessary pretreatment and deep physical and chemical treatment.

(1) Pretreatment dyeing wastewater has high pollution levels, large fluctuations in water quality and water content, and complex components. It generally requires pretreatment to ensure the biological treatment process's treatment effect and operational stability.

1: Adjustment (water quality and water leveling)

The quality of printing and dyeing wastewater varies greatly. Therefore, a regulating pool is generally set in the printing and dyeing wastewater treatment process to homogenize the quality of water and water. In order to prevent lint, cottonseed hull, and slurry from depositing at the bottom of the pool, water and air are often used in the pool. The mechanical stirring device stirs. The hydraulic retention time is generally about 8 hours.

2: The pH value of the neutralization printing and dyeing wastewater is often very high. In addition to adjusting its own acidity and alkalinity inhomogeneity by adjusting the pool, it is generally necessary to set a neutralization tank so that the pH of the wastewater meets the requirements of the subsequent treatment process. .

3: Waste chrome liquid treatment In the printing and dyeing plants with printing process, the printing drum needs to use **** when plating drums, and chromium pollution occurs when the drum is chrome stripped. These chromium-containing engraving wastes contain heavy metals and must be individually treated to eliminate chromium contamination.

4: Dye-concentrated foot-water pre-treatment dyeing The dye-draining foot water that is emitted when changing varieties is small in quantity, but the concentration is extremely high, and COD can reach tens or even hundreds of thousands. Separate pretreatment of this part of the wastewater can reduce the COD concentration of the wastewater, which is particularly important for small-batch, multi-species production companies.

(b) biological treatment technology Biological treatment process is mainly aerobic, currently used activated sludge, biological contact oxidation, biological carousel and tower biological filter. In order to improve the biodegradability of wastewater, anoxic and anaerobic processes have also been applied to the treatment of printing and dyeing wastewater.

1: Activated sludge method Activated sludge method is currently the most used method, there are push-flow activated sludge method, surface aeration tank and so on. Activated sludge method has the advantages of relatively low investment and good treatment effect. Among them, surface aeration tanks have been used in recent years because of the shortcomings such as short flow, inconvenient oxygenation and reflow adjustments, and the foaming coverage of water surface affecting oxygenation effects. The push-flow activated sludge process is still widely used in some large-scale industrial wastewater treatment stations.

The recommended sludge load is usually 0.3 to 0.4 kg (BOD5)/kg (MLSS)? d, its BOD5 removal rate is greater than 90%, COD removal rate is greater than 70%. According to the experience of Shanghai printing and dyeing industry, when the sludge load is less than 0.2kg (BOD5)/kg (MLSS)? At the time of d, the removal rate of BOD5 was up to 90%, and the COD removal rate was 60% to 80%.

2: Biological Contact Oxidation Biocontact Oxidation has special advantages such as high volume load, small footprint, little sludge, no expansion of filamentous bacteria, no need for sludge recirculation, easy management, special microorganisms that are easy to preserve and degrade special organic substances on the filler, etc. Due to its characteristics, it has been widely used in printing and dyeing wastewater treatment in recent years. After the biological contact oxidation method is stopped, the re-startup is quicker, and the impact on the biological treatment effect is less impact on the company's production-free wastewater discharge due to holidays and equipment maintenance. Therefore, although the biological contact oxidation method has a relatively high investment, it can be applied more and more widely because it can adapt to the difficult situation in which the enterprise's wastewater treatment management is low and the land is relatively tight. It is especially suitable for the treatment of printing and dyeing wastewater with medium and small amounts of water. Usually, the volumetric loading is 0.6-0.7 kg (BOD5)/kg (MLSS). At the time of d, the removal rate of BOD5 was 90%, and the COD removal rate was 60% to 80%.

3: Hypoxic hydrolysis aerobic biological treatment process As mentioned above, the role of the anoxic segment is to make part of the structure of the complex, difficult to degrade high-molecular organic matter, under the role of facultative microorganisms into small molecule organic matter, improve its Biochemical, and achieve a better treatment effect. The hydraulic retention time of the anoxic section is generally determined based on the influent COD concentration. When using the packing method in the anoxic section, it is generally recommended that the hydraulic retention time per 100mg/L of COD requires a cumulative value of 1h. The aerobic section load limit has two methods. First, the removal rate of the anoxic section is not counted. At this time, the aerobic section load limit is slightly higher than the general load value; the other calculation method is based on the anoxic section BOD5 removal rate is 20. %～30%, and the aerobic load is calculated as the general load value. After this process, the removal rate of BOD5 is above 90%, the COD removal rate is generally greater than 70%, and the color removal rate is also significantly higher than that of a single aerobic method.

4: Biorotary trays, tower filter biorotors, and tower filters have also been used in the treatment of printing and dyeing wastewater. Good results have been achieved, and some plants are still running. However, due to the large area of ​​these processes, the impact on the environment is always more, and the processing effect is lower than other processes, and it is rarely used at present.

5: Anaerobic treatment For the printing and dyeing wastewater with high concentration and poor biodegradability, the anaerobic treatment method can greatly increase the removal rate of organic matter. Anaerobic treatment has limited a series of results in laboratory research and pilot tests, and it is a promising new process. However, the production and operation management requirements are relatively high. After the anaerobic treatment method, aerobic treatment is required to meet the water quality requirements.

(III) Physico-chemical treatment and other treatment technologies In the treatment of printing and dyeing wastewater, commonly used physical and chemical treatment processes are mainly coagulation and sedimentation and coagulation and gas floatation. In addition, electrolysis, biological activated carbon, chemical oxidation, and the like are sometimes used in dyeing wastewater treatment.

1: coagulation method Coagulation method is the most used method in the treatment of printing and dyeing wastewater, there are two methods of coagulation and coagulation and flocculation. Coagulation has a good effect on removing COD and color. Coagulation can be set before or after biological treatment and sometimes as the only treatment facility.

When the coagulation method is set before the biological treatment, the amount of the coagulant to be added is large, the amount of sludge is large, the treatment cost is easily increased, and the difficulty of sludge treatment and final treatment is increased.

The COD removal rate of the coagulation method is generally 30% to 60%, and the BOD5 removal rate is generally 20% to 50%.

As an advanced treatment of wastewater, the coagulation method is provided after the biological treatment structure and has the advantage of flexible operation and operation. When the concentration of influent water is low and biochemical operation is effective, no coagulant can be added to save cost; when biological contact oxidation method is adopted, secondary sedimentation tank can be considered, so that the effluent of the biological treatment structure can directly enter the mixture. Condensate treatment facilities. In the treatment of printing and dyeing wastewater, coagulation is mostly set up after biological treatment. The COD removal rate is generally 15% to 40%.

When the concentration of original waste water pollutants is low and only the coagulation method can meet the discharge standard, only the coagulation method can be considered.

2: Chemical Oxidation Chemical Oxidation is generally used as an advanced treatment facility and is located at the end of the process flow. The main purpose is to remove chromaticity while also reducing some of the COD. After chemical oxidation treatment, the color can be reduced to less than 50 times, COD removal rate is low, generally only 5% to 15%. Commonly used decolorization methods include oxidation and adsorption. The oxidative decolorization method includes chlorine oxidation method, ozone oxidation method, and photooxidation method.

(1) Chlorine oxidative decolorization Chlorine has been widely used as a disinfectant for water treatment, and its function as an oxidant is different from that of sterilization. Chloro-oxidation and decolorization is the use of chromogenic organic compounds present in wastewater that are relatively easy to oxidize. Chlorine or its compounds are used as oxidants to oxidize organic compounds and destroy their structure to achieve decolorization.

Chlorine oxidants do not have decolorization efficiency for all dyes. For the easy oxidation of water-soluble dyes such as cationic dyes, azo dyes and easily oxidized insoluble dyes such as * dye, have a good decolorization effect. For water-insoluble dyes that are not easily oxidized, such as vat dyes, disperse dyes, and coatings, the decolorization effect is poor. When wastewater contains more suspended solids and slurries, this method can not only remove such substances but also consume large amounts of oxidants. Moreover, during the oxidation process, not all dyes are destroyed, most of which are present in the effluent in the oxidized state. After being placed, some of them may recover their original colors. Therefore, decolorization by using this method alone is not ideal, and it should be combined with other methods to obtain a better decolorization effect.

Chlorine oxidants are commonly used **, bleach and sodium hypochlorite.

(2) Ozone Oxidation Decolorization As a strong oxidant, ozone is also widely used in decolorization and advanced treatment of wastewater. The reason why ozone has a strong oxidizing effect was once thought to be the formation of a new ecological atomic oxygen during decomposition, which is manifested as a strong oxidant. At present, it is believed that the oxygen atoms in the ozone molecules are themselves strongly electrophilic or pro-protonic, and the direct manifestation of strong oxidants is the main reason.

The color development of dyes is caused by their chromophoric groups, such as vinyl, azo, oxy-oxy, carbonyl, *keto, nitroso, vinylene, and the like. Each of these chromophoric groups has an unsaturated bond, and ozone can oxidize and decompose these groups contained in the dye to generate organic acids and aldehydes having a relatively low molecular weight and lose their coloring ability. Therefore, ozone is a good decolorizer. However, due to the different types of dyes, the position of their chromophoric groups is different, and their decolorization rates are also quite different. For dyes containing water-soluble dyes, such as active, direct, cationic and acidic dyes, the decolorization rate is high. Wastewater containing insoluble disperse dyes also has good decolorization effect. However, insoluble dyes, such as reducing, bleaching, and coating, which are present in the waste water in a finely dispersed suspension, have a poor decolorization effect.

(3) Photooxidation Decoloration Photooxidation decolorization is a process that uses the strong oxidation generated by the combined action of light and oxidant to oxidize and decompose organic contaminants in the wastewater, resulting in a significant decrease in BOD, COD, and color of the wastewater. method.

The oxidant commonly used in photooxidation is **, and the effective light is ultraviolet light. UV light catalyzes the decomposition of oxidants and the oxidation of pollutants. Sometimes, some special wavelengths of light have special effects on certain substances. Therefore, the design should choose the appropriate special UV lamp as a light source.

The characteristics of photooxidation and decolorization are: strong oxidation, no sludge production, wide application range, advanced treatment of wastewater, compact equipment, and small footprint. Photo-oxidation bleaching and printing and dyeing wastewater, except for a small part of disperse dyes, the decolorization effect is poor, the decolorization rate of other dyes are more than 90%.

3: The electrolysis method generates a chemical reaction by the action of an impressed current. The process of converting electric energy into chemical energy is called electrolysis. The use of electrolytic chemical reactions to convert waste water into harmful impurities is called the wastewater electrolysis process, or electrolysis.

In the past, electrolysis was mostly used to treat cyanide-containing and chromium-containing electroplating wastewater. In recent years, it has only begun to be used for the treatment of textile printing and dyeing wastewater, but it still lacks mature experience. Studies have shown that the decolorization effect of electrolysis is significant. For some reactive dyes, direct dyes, mordant dyes, bleaching dyes, and disperse dye printing and dyeing wastewater, the decolorization rate can reach more than 90%, and the decolorization rate of acid dye wastewater can reach over 70%. The electrolysis method has the characteristics of simple equipment, convenient management, and good effect for the treatment of a small amount of printing and dyeing wastewater. Fixed bed electrolysis has also been applied in engineering and has achieved good results. The disadvantage is that it consumes more power and consumes more electrodes, which is not suitable when the amount of water is large. Electrolysis is generally treated as an advanced treatment and is set after biological treatment. The COD removal rate is 20% to 50%, and the color can be reduced to less than 50 times.

When the concentration of raw wastewater is low and the discharge standard can only be achieved by electrolysis, only electrolytic treatment facilities may be considered. When treated with the electrolytic method alone, the COD removal rate was 40% to 75%.

Electrolysis has the following characteristics:

(1) The reaction speed is fast, the decolorization rate is high, and the amount of mud produced is small;

(2) Operating at normal temperature and pressure, easy to manage and easy to automate;

(3) When the concentration of pollutants in the influent water changes, it can be controlled by adjusting the voltage and current to ensure the stability of the effluent water quality;

(4) Short processing time, small equipment volume, small footprint;

(5) DC current is needed for electrolysis. The power consumption and electrode consumption are relatively large. It is suitable for the treatment of small amount of waste water.

4: Activated Carbon Adsorption Process Activated carbon adsorption technology has been used for many years in the refining and decolorization of pharmaceutical, chemical and food industries in China. The 70s began to be used for industrial wastewater treatment. Production practice shows that activated carbon has excellent adsorption of trace organic pollutants in water. It has good adsorption effect on industrial printing and dyeing, dye chemicals, food processing and organic chemicals. Under normal circumstances, organic substances represented by comprehensive indicators such as BOD and COD in waste water, such as synthetic dyes, surface agents, phenols, benzenes, organic chlorine, pesticides, and petrochemical products, have unique removal capabilities.

Adsorption is the process by which a substance attaches to the surface of another substance. Adsorption is an interfacial phenomenon that is related to changes in surface tension and surface energy. There are two kinds of promoting ability to cause adsorption, one is the repellent force of solvent water on hydrophobic substances, and the other is the affinity affinity of solids to solute. Adsorption in wastewater treatment is mostly the result of the combined effects of these two forces. The specific surface area and pore structure of activated carbon directly affect its adsorption capacity. When selecting activated carbon, it should be determined by tests according to the quality of wastewater.

For the printing and dyeing wastewater, it is better to choose the carbon species with developed transition holes. In addition, ash also has an effect, and the smaller the ash content, the better the adsorption performance. The closer the adsorbate molecule size is to the pore diameter of the carbon, the easier it will be to adsorb. The adsorption concentration of activated carbon also affects the adsorption capacity of activated carbon. In a certain concentration range, the amount of adsorption increases with the concentration of adsorbate. In addition, water temperature and pH also have an effect. The amount of adsorption decreases with increasing water temperature and increases with decreasing pH. Therefore, low water temperature and low pH are conducive to the adsorption of activated carbon.

Activated carbon adsorption method is suitable for use as a small amount of water, and general biochemical and physicochemical methods cannot handle advanced treatment methods at the time of compliance. Its advantage is good effect, the disadvantage is high operating cost.