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Application areas of membrane separation technology: The development and application of membrane separation technology have enabled many industries, such as pure water production, seawater desalination, brackish water desalination, the electronics industry, pharmaceuticals and bioengineering, environmental protection, food processing, the chemical industry, and textiles, to solve problems related to separation, concentration, and purification with high quality. It provides the technical foundation for a circular economy and clean production. 1 Introduction to Membrane Separation Technology 1.1 Definition of Membranes A membrane is a medium that enables molecular-level separation and filtration. When a solution or a mixed gas comes into contact with a membrane, under pressure, the action of an electric field, or a temperature difference, certain substances can pass through the membrane while others are selectively retained. This allows for the separation of different components within a solution or a mixed gas; it is a molecular-level separation process. 1.2 Types of membranes Separation membranes include: reverse osmosis membranes (0.0001–0.005 μm), nanofiltration membranes (0.001–0.005 μm), ultrafiltration membranes (0.001–0.1 μm), microfiltration membranes (0.1–1 μm), electrodialysis membranes, pervaporation membranes, liquid membranes, gas separation membranes, electrode membranes, etc. They correspond to different separation mechanisms, different equipment, and have different application targets. The membrane itself can be made of polymers, inorganic materials, or liquids; its structure can be homogeneous or heterogeneous, porous or non-porous, solid or liquid, charged or neutral. The thickness of the membrane can range from as thin as 100μm to several millimeters. Different membranes have distinct microstructures and functions, requiring different methods for preparation. Film formation methods have always been a core research topic in the field of membranes, as well as a closely guarded core technology by various companies. 1.3 Definition of membrane separation technology The aforementioned membranes are configured for industrial use, and combined with driving equipment (pressure pumps, electric fields, heaters, or vacuum pumps), valves, instruments, and pipelines to form a complete system. By operating under certain process conditions, it is possible to separate aqueous solutions or mixed gases. The component that passes through the membrane is called the permeate fraction. This separation technique is known as membrane separation technology. 2 Application Areas of Membrane Technology 2.1 Water Supply 2.1.1 Provision of High-Quality Drinking Water As water bodies become more polluted and living standards rise, people increasingly desire access to high-quality drinking water. The combination of activated carbon adsorption filtration and ultrafiltration is used to produce high-quality drinking water. It requires low investment in equipment and results in low production costs, making it an economical and effective method for producing high-quality drinking water with broad market prospects. 2.1.2 Industrial water supply The quality of tap water and groundwater does not meet the requirements of many chemical, electronics, and textile industries; it must be purified before it can be used. Ultrafiltration membrane technology is one of the important techniques for purifying industrial water. 2. 1. 3 Pharmaceutical water Pharmaceutical water used for injections is prepared through multi-stage distillation; this process is complex, energy-intensive, and the quality of such water often cannot be guaranteed. Using ultrafiltration membrane technology to remove pyrogens from injections and end-water pyrogens has yielded excellent results. 2.2 Treatment of process water (separation, concentration, classification, and purification) In various industrial production processes, there is often a need to separate, concentrate, classify, and purify certain aqueous solutions. Traditional methods involve processes such as precipitation, filtration, heating, freezing, distillation, extraction, and crystallization. These methods have disadvantages such as long processes, high energy consumption, significant material loss, large-sized equipment, low efficiency, and complicated operations. Replacing a certain traditional technology with ultrafiltration membrane technology can yield substantial economic benefits. 2.2.1 Applications of membrane technology in the pharmaceutical industry Membrane technology is widely used for separation, concentration, and purification in biological production and pharmaceutical manufacturing. Such as the separation of blood components, the purification of antibiotics and interferons, the fractionation and purification of proteins, as well as the sterilization and clarification of traditional Chinese herbal preparations. Fermentation is the mainstream technology in biopharmaceuticals for extracting drugs from fermentation broths. Traditional methods involve solvent extraction or thermal concentration, with repeated use of organic solvents and acid-base solutions, resulting in high consumption, long processes, and significant wastewater treatment requirements. In particular, many drugs are highly sensitive to heat, which limits the practicality of traditional manufacturing processes. Internationally advanced pharmaceutical production lines make extensive use of membrane separation technology to replace traditional separation, concentration, and purification processes. Such as concentrating and purifying antibiotics using membrane equipment, as well as clarifying traditional Chinese medicine decoctions and injections. 2.2.2 Industrial applications of membrane technology in the food industry: Ultrafiltration membrane technology is used to separate the products in the fermentation broth from the microorganisms, followed by further purification processes using other methods. Its advantages are: improved production efficiency and product quality; simplified process flow; the bacterial protein contains no external impurities, giving it high value for use and enabling comprehensive utilization of resources. Membrane technology is used in the clarification of soy sauce and vinegar, the clarification and concentration of fruit juices, dairy production, and the sugar industry. 2.2.3 Applications of membrane technology in various industrial processes Any process involving molecular-level concentration and separation presents an opportunity for the use of membrane technology. Online purification of automotive electrophoretic paint uses ultrafiltration membranes to remove impurities, thereby ensuring consistent paint quality; in the fuel industry, ultrafiltration membrane technology is used to separate and concentrate intermediates. 2.3 Applications in environmental protection and water resource utilization Membrane technology is widely used in wastewater treatment, pollution control, and the comprehensive utilization of water resources. In many cases, not only is wastewater treated, but useful substances and energy can also be recovered. 2. 3. 1 Treatment of various oil-containing wastewater and used oils ① Treatment of water used for oil recovery injection: Membrane technology can remove the emulsified and dissolved oils in water, thereby improving the quality of the injection water. ②Treatment of oily wastewater: Many industries in the fields of production and transportation generate large amounts of oily wastewater, and membrane filtration technology is the most effective method for ensuring compliance with discharge standards. ③Purification of used lubricating oil: By using conventional techniques along with membrane separation, highly pure lubricating oil can be obtained, which is suitable for the treatment of used oil from vehicles and similar applications. ④Purification and recycling of machine tool cutting oil: Membrane technology can remove bacteria and impurities from waste cutting oil, allowing it to be reused after treatment. ⑤Purification techniques for used cooking oil: Cooking oil generates carcinogenic substances under continuous high temperatures, and these can be removed using membrane filtration. ⑥Purification of edible rapeseed oil: Rapeseed oil contains 15% to 48% erucic acid, which has a high carbon content. It can be removed by membrane filtration to meet the standard (erucic acid < 5%). 2. 3. 2 Wastewater treatment and reuse ①Membrane bioreactors are used to treat domestic wastewater and reuse the resulting water; they require less space, have lower equipment costs, and produce high-quality treated water. ②For the treatment and reuse of printing and development wastewater, membrane technology can be used to ensure compliance with discharge standards as well as to enable wastewater recovery. ③Electroplating wastewater can be treated using membrane technology, with water reused and pollutants recycled back into the process. ④Membrane separation can be used to remove colored dyes from printing and dyeing wastewater, and the resulting water can be reused. Indigo fuel can be recovered from denim printing and dyeing wastewater. ⑤Membranes used for papermaking wastewater can separate substances such as lignin and pigments from the wastewater, allowing the purified water to be discharged or reused.