Application of Ultrafiltration in Water Treatment
Ultrafiltration is a kind of membrane system between microfiltration and nanofiltration. The average pore size is 3-100nm. Ultrafiltration membrane is a membrane separation technology that can purify, separate, and concentrate the solution. The mechanism of trapping is mainly Screening effect, but sometimes the membrane pores are larger than the solvent molecules, and larger than the solute molecules. The chemical properties of the surface of the femoral membrane also play a role in trapping, with the pressure difference between the membranes as the driving force and the ultrafiltration membrane as the driving force. The filter medium, under certain pressure, allows water and low molecular weight solutes to pass when the water flows over the membrane surface, thereby achieving the purpose of purification, separation, and concentration of the solution.
1. Drinking water treatment Ultrafiltration generally can remove microorganisms such as leeches, algae, protozoa, bacteria and even viruses from the water, and combine with the second-generation treatment process to give full play to the advantages of various processes, and to pathogenic microorganisms in water. Turbidity, natural organic matter, trace organic contaminants, ammonia nitrogen, etc. have better out-going effects, thereby satisfying people's increasing demands for water quality.
2. Wastewater treatment According to various characteristics of ultrafiltration membranes, whether it is in domestic sewage or industrial wastewater, it is widely used. After domestic sewage is treated by ultrafiltration, the treated water quality becomes better and reused, and the industrial wastewater can meet the standards due to the general technical department. Ultrafiltration technology can fully treat wastewater.
1) Domestic sewage treatment Urban wastewater treatment plant wastewater can be treated with ultrafiltration membrane technology. The treated water quality is good, can be used for the reuse of water, and the reactor covers an area of small, low investment in equipment, can be widely used Residential water reuse.
2) Oily Wastewater Treatment Oily waste water exists in three states: oil slick, dispersed oil, emulsified oil, and money are easier to handle. Mechanical separation, flocculation and sedimentation, and activated carbon adsorption can reduce the fraction to a very low level. Emulsified oils contain organic substances that have the same effects as surfactants and gases. Oils in micron-sized ions exist in water. Gravity separation and coarse granulation methods are difficult. Ultrafiltration membranes can achieve their goals. They enable water and low-molecular-weight organics to pass through membranes. , In order to achieve oil-water separation, for example, the oil content in the oil-bearing wastewater is usually 100-1000 mg/L, so the defibration must be performed before the application of hollow fiber ultrafiltration membrane technology, so that the wastewater after treatment reaches 100mg/L.
3) Wastewater treatment in food industry Wastewater formed in the processing of milk, beverages, starch, yeast, tofu, and meat in the food industry contains a large amount of protein, starch, yeast, lactose, and fat, all of which have a certain recovery value. The BOD and COD in such waste water are relatively high, which will cause environmental pollution, and are difficult to handle with general biochemical methods, and there is no need to recover the useful substances. The use of ultrafiltration can achieve the purpose of purifying the waste water.
4) Electroplating wastewater treatment The electroplating wastewater has high water consumption. Among them, heavy metal ions such as cyanide, hexavalent chromium, nickel, copper, zinc, iron, and septum are very toxic and cause serious damage to humans, Dongwu and crops. influences. Electroplating wastewater is characterized by biodegradability, and the metal ions inside are difficult to be absorbed by microorganisms. Using ultrafiltration membrane and reverse osmosis can make the outflow of nickel, nitrate, and total organic carbon in nickel-plating wastewater at 97%, 99.8%, 95%, and 87%, respectively, through the ultrafiltration membrane as a pretreatment. The reverse osmosis membrane contamination is significantly reduced, and the reverse osmosis membrane flux can be increased by 30-50%.
5) Treatment of papermaking wastewater UF is used in papermaking wastewater, mainly for the concentration and recovery of certain components, and the returned water is returned to the process for use. The main material recovered is sulfonated lignin. He can Returning pulp to reuse can create greater environmental and economic benefits.
6) The desalination of small-scale desalination devices has clearly demonstrated that the ultrafiltration system can effectively control the quality of seawater and provide high-quality influent water for reverse osmosis systems. Long-term tests have shown that the SDI value of the effluent of ultrafiltration systems can be very good. With no load below 2, these tests do not have to be pre-treated before the UF system and are suitable for various seawater quality. The role of ultrafiltration bactericide in the system Because the material separation function of the ultrafiltration system depends on the membrane, it is the same as the separation equipment of other membranes. In the process of use, membrane fouling and flux decline will always occur. The main cause of membrane fouling is biological contamination. The flux caused by membrane fouling is irreversible, and its severity is enough to make the process difficult to carry out, resulting in a series of adverse consequences such as reduced desalination efficiency of the device and shortened service life. System Maintenance and Preventive Control The most common method to solve this problem is to add special bactericidal agents to the influent water of the ultrafiltration system. The optimal sterilization frequency should be determined according to the actual conditions of each system. There are two methods of sterilization. Batch and continuous dosing options are available. In the operation of the ultrafiltration system, the research on ultrafiltration membrane contamination control should be focused on in order to prevent problems before it can be optimized and promoted in terms of system economics, environmental protection, and operation management.