-
E-mail
450883224@qq.com
-
Phone
15810969854
-
Address
No. 51 Shunren Road, Linhe Industrial Development Zone, Shunyi District, Beijing
Zhongke Ruiyang Membrane Technology (Beijing) Co., Ltd
Treatment of Printing and Dyeing Wastewater with Roll type Membrane Combination Process
Date: 2025-05-14Read: 8
The textile printing and dyeing industry is an important component of China's industry, with a large amount of wastewater, accounting for about 35% of industrial wastewater discharge. The amount of printing and dyeing wastewater is large, the content of organic pollutants is high, the alkalinity and pH values change greatly, and the water quality changes greatly; Poor biodegradability, the BOD5/COD value of wastewater is generally around 20%; High chromaticity, sometimes up to 4000 times or more; In the printing and dyeing industry, the use of PVA slurry and new additives greatly increases the content of difficult to biodegrade organic matter in wastewater.
1. Introduction to membrane technology
The reuse of wastewater by membrane method mainly includes the process flow of "ultrafiltration membrane+reverse osmosis membrane". Ultrafiltration (UF) is a pressure driven membrane separation process that can separate particulate matter from fluids and dissolved components. The typical pore size of ultrafiltration membrane is between 0.01~0.1 μ m, which has a high removal rate for bacteria, most pathogens, colloids, sludge, etc. Reverse osmosis (RO) pretreatment transfers the problem of pollution to ultrafiltration, which is solved by UF or MBR. Using UF or MBR as pretreatment only reduces pollution, but many factors still need to be considered in the RO part, such as the selection, arrangement, and economic operation of membrane elements. Due to the varying precision of each membrane component, strict requirements are placed on the quality of the source water to ensure long-term and stable operation of the equipment. The molecular weight cut-off of ultrafiltration is between 10000 and 50000 daltons, with a maximum filtration accuracy of 0.1-0.2 μ m. The molecular weight cut-off of nanofiltration membrane components is between 200 and 2000 daltons; Reverse osmosis has a molecular weight cutoff of approximately 50 daltons.
2. Application of membrane technology in the treatment of printing and dyeing wastewater
Regarding the characteristic of printing and dyeing wastewater being a typical industrial organic wastewater with poor biodegradability and containing difficult to degrade water-soluble organic pollutants SS、 Due to the characteristics of colloidal substances, the "double membrane method" treatment process is adopted, which can not only recover water resources and achieve wastewater recycling, but also further reduce the total amount of sewage discharge.
The water reuse project of a certain printing and dyeing company's printing and dyeing wastewater consists of two systems: one is the construction of a 20000 m3/d physicochemical and biochemical treatment system, which reduces the COD concentration of the printing and dyeing wastewater to 100-200 mg/L; Secondly, a membrane treatment system with a capacity of 8000m3/d for advanced wastewater treatment has been built. The "dual membrane method" technology is used to further treat the printing and dyeing wastewater, and all of it is reused in production. The membrane performance parameters used in this project are detailed in Table 1. The project has a sewage treatment capacity of 20000 m3/d, of which 8000 m3/d is reused, covering an area of 20000 square meters and a building area of 3000 square meters.
If the wastewater that has undergone secondary biochemical treatment is directly subjected to reverse osmosis, due to the presence of a certain amount of organic matter and impurities in the water, it is highly prone to membrane fouling and blockage of membrane pores. Therefore, the wastewater can be effectively reduced from membrane fouling by first undergoing ultrafiltration pretreatment and then undergoing security filtration. The water quality before and after treatment is detailed in Tables 2 and 3.
The process flow adopted in this project is shown in Figure 1.
Figure 2 shows the relationship between MBR membrane water production flux and operating pressure. It can be seen that the MBR membrane water production flux decreases relatively smoothly with the increase of membrane negative pressure. As the pressure increases, membrane fouling intensifies, and the flux no longer increases linearly with increasing pressure, but gradually tends to flatten out. This may be due to the fact that the higher the pressure, the denser the fouling layer, resulting in an increase in membrane fouling resistance.
Zhongke Ruiyang MBR adopts air blowing aeration as the membrane cleaning equipment. The bubbles generated by air blowing aeration rub against the membrane surface, greatly reducing the adhesion of pollutants to the membrane surface; Due to the fixed permeable pore size, the water quality is relatively stable; The equipment can accept suspended solids concentrations with high loads, up to 18000mg/l, which can save sedimentation space or eliminate sedimentation tanks while ensuring the quality of the produced water.
Compared with traditional biological treatment methods and ultrafiltration technology, MBR has the advantages of high biochemical efficiency, strong resistance to load shock, stable effluent quality, small footprint, long sludge discharge cycle, and easy implementation of automatic control. It is currently one of the most promising new technologies for wastewater treatment. From Figure 3, it can be seen that the water production rate of the RO membrane decreases relatively smoothly with increasing operating time.
The performance of membrane recycling system equipment will also vary greatly with temperature changes. The inlet water temperature will cause changes in the diffusion rate of membrane components, firstly, the amount of water produced will decrease with decreasing temperature; Secondly, the quality of the produced water increases with decreasing temperature; Once again, the operating pressure increases as the temperature decreases. Based on the membrane performance design parameters, it is recommended to use an operating temperature of 25 ℃ as the optimal temperature.
Figure 4 shows the relationship between RO desalination rate and time. It can be seen that the desalination rate of RO membrane is very high, basically around 99%. More than 96%. The percentage of dissolved impurities in raw water passing through the membrane is calculated as SP=100% × (Cp/Cfm) (1)
Where:
SP - Salt penetration rate,%;
Cp - permeate salt concentration;
Cfm - the average salt concentration of the feed solution.
The basic relationship between water flux and salt permeability is the fundamental principle of reverse osmosis. It can be seen that the salt permeability decreases with increasing operating pressure, because the water flux increases with pressure, but the salt permeability rate remains unchanged under pressure changes.
From Figure 5, it can be seen that the operating pressure of the RO membrane is relatively stable, with a low pressure difference of only 0 before and after the membrane. About 3 MPa.
Reverse osmosis membrane separation technology achieves wastewater treatment by separating, concentrating, and recovering pollutants from wastewater. It has the characteristics of no secondary pollution, low energy consumption, and recyclability. After a period of use, the surface of the membrane element will form a scale layer composed of impurities such as silicon scale, calcium scale, magnesium scale, metal oxides, organic matter, etc., which is generally manifested in changes in the operating parameters of the system, such as a decrease in water production, an increase in operating pressure, a deterioration in water quality, and an increase in pressure difference between membrane segments (the above data are standardized data). Generally, when the above parameters increase or decrease by 10-15%, chemical cleaning is required. Through physical and chemical reactions such as soaking, reaction, and flushing with chemical solutions, the scale layer is loosened and flushed out of the membrane to restore the operating performance of the membrane element.
After being treated with reverse osmosis membrane equipment, the salt content and conductivity of the wastewater are greatly reduced, reaching or exceeding the water standards for printing and dyeing industry, which can meet the production needs of medium and high-end products. In actual production, the recycled water treated by reverse osmosis can be mixed with general production water in a certain proportion to improve the water quality of normal production water and reduce water costs.