1. Main methods of printing and dyeing wastewater treatment
Printing and dyeing wastewater is mainly composed of organic pollution , organic wastewater with complex composition, the main objects of treatment are BOD5, organic matter that is not easy to biodegrade or biodegrades slowly, alkalinity, dyes and pigments, and a small amount of toxic substances. Although the biodegradability of printing and dyeing wastewater is generally poor, except for individual printing and dyeing wastewater (such as chemical fiber fabric dyeing), it is still biodegradable organic wastewater. The treatment method is mainly biological treatment, supplemented by necessary pretreatment and physical and chemical in-depth treatment.
2. Pretreatment
Printing and dyeing wastewater has a high degree of pollution and poor water quality. , The water volume fluctuates greatly and the ingredients are complex, so pretreatment is generally required to ensure the treatment effect and operational stability of the biological treatment method.
1. Adjustment (water quality and water quantity homogenization)
For example As mentioned above, the water quality and quantity of printing and dyeing wastewater vary greatly. Therefore, a regulating tank is generally installed in the printing and dyeing wastewater treatment process to homogenize the water quality and quantity. In order to prevent fiber scraps, cottonseed hulls, slurry, etc. from settling at the bottom of the pool, hydraulic, air or mechanical stirring equipment is commonly used in the pool for stirring. The hydraulic retention time is generally about 8 hours.
2. Neutralization
The pH of printing and dyeing wastewater is often very high , in addition to homogenizing its own acid and alkalinity unevenness through the adjustment pool, it is generally necessary to set up a neutralization pool. In order to make the pH of the wastewater meet the requirements of the subsequent treatment process.
3. Waste chromium liquid treatment
In areas with printing process In printing and dyeing factories, potassium dichromate, etc. are used when plating printing rollers. Chromium pollution will occur when the rollers are stripped of chromium. These chromium-containing engraving wastewater must be treated separately to eliminate chromium contamination.
4. Pretreatment of dye concentrated water
The amount of dye-concentrated water discharged when changing varieties is small, but the concentration is extremely high, and the COD can reach tens of thousands or even hundreds of thousands. Separate pretreatment of this part of wastewater can reduce the COD concentration of the wastewater, which is especially important for small-batch, multi-variety production companies.
3. Biological treatment technology
Biological treatment technology is mainly used Oxygen method, currently used include activated sludge method, biological contact pump method, biological turntable and tower biological filter, etc. In order to improve the biodegradability of wastewater, anoxic and anaerobic processes have also been used in printing and dyeing wastewater treatment.
1. Activated sludge method
The activated sludge method is The most commonly used methods at present include push-flow activated sludge method, surface aeration tank, etc. The activated sludge method has the advantages of relatively low investment and good treatment effect. Among them, the surface aeration tank has been rarely used in recent years due to its shortcomings such as short flow, inconvenient adjustment of oxygenation volume and return volume, and the generation of foam covering the surface water when there is a large amount of surfactant, which affects the oxygenation effect. The push-flow activated sludge method is still widely used in some large-scale industrial wastewater treatment stations. The recommended value of sludge load is usually 0.3~0.4kg(BOD5)/kg(MLSS)·d, with a BOD5 removal rate greater than 90% and a COD removal rate greater than 70%. According to experience in the printing and dyeing industry, when the sludge load is less than 0.2kg (BOD5)/kg (MLSS)·d, the BOD5 removal rate can reach more than 90%, and the COD removal rate can reach 60% to 80%.
2. Biological contact oxidation method
Biological contact oxidation method has It has the characteristics of high volume load, small area, less sludge, no expansion of filamentous bacteria, no need for sludge return, easy management, and easy preservation of specialized microorganisms that degrade special organic matter on the filler. Therefore, it has been used in printing and dyeing wastewater treatment in recent years. broadly used. After the biological contact oxidation method is stopped, it can be restarted quickly. If the company stops production due to holidays and equipment maintenance, no wastewater discharge will have little impact on the biological treatment effect. Therefore, although the investment in the biological contact oxidation method is relatively high, its application is becoming more and more widespread because it can adapt to difficult situations such as low corporate wastewater treatment management levels and tight land use. It is especially suitable for the treatment of printing and dyeing wastewater with small and medium water volumes. Usually when the volume load is o.6~0.7kg(BOD5)/kg(MlSS)·d, the BOD5 removal rate is greater than 90%, and the COD removal rate is 60%~80%.
3. Anoxic hydrolysis and aerobic biological treatment process
For example As mentioned before, the role of the anoxic section is to convert some complex-structured, difficult-to-degrade polymer organic matter into small molecular organic matter under the action of facultative microorganisms, thereby improving its biodegradability and achieving better treatment effects. . The hydraulic retention time in the anoxic section is generally determined based on the COD concentration of the incoming water. When the packing method is used in the anoxic section, it is usually recommended to calculate the cumulative value based on the required hydraulic retention time of 1 hour per 100 mg/L of COD. There are two methods for the load limit of the aerobic section. One is to exclude the removal rate of the anoxic section. At this time, the load limit of the aerobic section is slightly higher than the general load value; the other calculation method is to use the BOD5 removal rate of the anoxic section of 20 %~30%, and the load of the aerobic section is calculated according to the general load value. After this process, the BOO5 removal rate is above 90%, the COD removal rate is generally greater than 70%, and the chroma removal rate is also significantly improved compared to the single aerobic method.
4. Biological turntable, tower filter
Biological turntable Processes such as tower filters and tower filters have also been used in the treatment of printing and dyeing wastewater, and have achieved good results. Some factories are currentlyThere are two types of forces, one is the repulsive force of solvent water on hydrophobic substances, and the other is the affinity attraction of solids on solutes. Adsorption in wastewater treatment is mostly the result of the combined action 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 through experiments based on the quality of wastewater. For printing and dyeing wastewater, it is better to choose carbon species with developed transition pores. In addition, the ash content also has an impact. The smaller the ash content, the better the adsorption performance; the closer the size of the adsorbate molecules is to the carbon pore diameter, the easier it is to be adsorbed; the adsorbate concentration also has an impact on the adsorption capacity of activated carbon. Within a certain concentration range, the adsorption capacity is It increases with the increase of adsorbate concentration. In addition, water temperature and pH also have an impact. The adsorption capacity decreases with the increase of water temperature and increases with the decrease of pH. Therefore, low water temperature and low pH are conducive to the adsorption of activated carbon.
The activated carbon adsorption method is more suitable for in-depth treatment when the amount of water is small and general biochemical and physicochemical methods cannot meet the standards. Its advantage is good effect, but its disadvantage is high operating cost. </p
