Ion exchange and RO

I don't know much about the principle of RO membrane about ion exchange. There is no unified view yet. You can check the relevant information. Scope of application: The range is relatively wide. In terms of TDS, the inlet water TDS is preferably lower than 50000mg/L. ； In terms of pH, the general pH range of incoming water is 3~12 (some manufacturers may claim it is 2~13) ； In terms of water quality: It is best that the incoming water does not contain oxidizing substances (reverse osmosis membranes made of aromatic polyamide are not very resistant to oxidation. Unfortunately, most reverse osmosis membranes are now made of this material) ； In terms of pollution: It is best that the incoming water does not contain contaminants such as organisms and scaling that can cause the membrane system to produce organisms. The cleaning method depends on the type and degree of system contamination. For maintenance cleaning, it is recommended to do it once every six months. Does condition refer to operating condition? This depends on the membrane user manual of each manufacturer. time? I don’t quite understand what you want to ask!

In ion exchange desalination, the acid and alkali used pollute the environment. RO is a reverse osmosis water treatment desalination device, which is relatively environmentally friendly and has a water output efficiency of about 75%. If the requirements for water are higher, ion exchange can be connected in series later to prepare high-purity water.

Water with a high salt content is relatively easier to use than ion exchange. The advantage is that it reduces the consumption of acid and alkali and reduces the workload of workers for regeneration. The disadvantage is that the one-time investment is higher than that of ion exchange. If the pretreatment design is unreasonable, the membrane will be cleaned more frequently.

1. Osmosis and Osmotic Pressure Osmotic phenomena are common in nature. For example, if a cucumber is placed in salt water, the cucumber will become smaller due to water loss. The process of water molecules in cucumber entering the salt water solution is the osmosis process. As shown in Figure 1, if a pool is divided into two parts with a membrane that only water molecules can pass through, pure water and salt water are injected on both sides of the membrane to the same height. After a while, you will find that the liquid level of pure water decreases, while the liquid level of salt water increases. We call the phenomenon of water molecules migrating into salt water through this membrane osmosis. The rise of the salt water level is not endless. It will reach an equilibrium point when it reaches a certain height. At this time, the pressure represented by the difference in liquid levels at both ends of the diaphragm is called osmotic pressure. The magnitude of osmotic pressure is directly related to the concentration of salt water. 　　 2. After the reverse osmosis phenomenon and reverse osmosis water purification technology reach equilibrium in the above device, if a certain pressure is exerted on the liquid surface of the brine end, water molecules will migrate from the brine end to the pure water end. The process in which liquid molecules migrate from a dilute solution to a concentrated solution under pressure is called reverse osmosis. If we add salt water to one end of the above facility and apply a pressure at that end that exceeds the osmotic pressure of the salt water, we can get pure water at the other end. This is the principle of reverse osmosis water purification. There are two keys to producing pure water in reverse osmosis facilities. One is a selective membrane, which we call a semipermeable membrane, and the other is a certain pressure. Simply put, there are numerous pores on the reverse osmosis semi-permeable membrane, and the size of these pores is equivalent to the size of water molecules. Since bacteria, viruses, most organic pollutants and hydrated ions are much larger than water molecules, they cannot pass through the reverse osmosis semi-permeable membrane and are separated from the water that passes through the reverse osmosis membrane. Among the many impurities in water, soluble salts are the most difficult to remove. Therefore, the water purification effect of reverse osmosis is often determined based on the salt removal rate. The salt removal rate of reverse osmosis is mainly determined by the selectivity of the reverse osmosis semipermeable membrane. At present, the salt removal rate of highly selective reverse osmosis membrane elements can be as high as 99.7%. 　　 3. Comparison between reverse osmosis and ion exchange Advantages of reverse osmosis: Continuous operation, stable product water quality, no need for acid and alkali regeneration, no shutdown due to regeneration, saving water for backflushing and cleaning, and producing ultrapure water with high yield (the yield can be as high as 95%) No regeneration sewage, no sewage treatment facilities, no acid-base reserves and acid-base dilution transportation facilities required, reduced workshop building area, safe and reliable use, avoid workers' exposure to acids and bases, reduce operation and maintenance costs, simple installation, low installation costs. Weaknesses and solutions of reverse osmosis equipment. The system salt removal rate of reverse osmosis equipment is generally 98-99%. Such a salt removal rate can meet the requirements in most cases. In the electronics industry, ultra-high pressure boiler feed water, and individual pharmaceutical industries, the requirements for pure water may be higher. At this time, single-stage reverse osmosis equipment cannot meet the requirements. The following methods can further purify reverse osmosis water to meet the requirements: 1: Double-stage reverse osmosis performs a reverse osmosis treatment on the single-stage reverse osmosis pure water to improve the purity of the pure water. 2: The combination of reverse osmosis and EDI can produce ultrapure water with smaller factory buildings and lower operating costs. 3: The combination of reverse osmosis and ion exchange can reduce the plant area and lower operating costs. A membrane that is selective for the substances that pass through it is called a semipermeable membrane. Generally, a membrane that can only pass through solvent but cannot pass through solute is regarded as an ideal semipermeable membrane. When the same volume of dilute solution (such as fresh water) and concentrated solution (such as seawater or salt water) are placed on both sides of a container, separated by a semipermeable membrane in the middle, the solvent in the dilute solution will naturally pass through the semipermeable membrane and flow to the concentrated solution side. The liquid level on the concentrated solution side will be a certain height higher than the liquid level of the dilute solution, forming a pressure difference and reaching an osmotic equilibrium state. This pressure difference is the osmotic pressure. The size of the osmotic pressure depends on the type of concentrated solution, and the concentration and temperature have nothing to do with the properties of the semipermeable membrane. If a pressure greater than the osmotic pressure is applied to the side of the concentrated solution, the solvent in the concentrated solution will flow toward the dilute solution. The flow direction of the solvent is opposite to the original direction of penetration. This process is called reverse osmosis. Reverse osmosis is a pressure-driven separation method that uses the selective interception of a semipermeable membrane to separate solutes and solvents in a solution. It is currently widely used in the separation and concentration of various liquids. In the water treatment process, impurities such as inorganic ions, bacteria, viruses, organic matter, and colloids are removed from the water to obtain high-quality water. At present, reverse osmosis membranes are mainly composed of two major types of materials, one is cellulose acetate (CA) and the other is polyamide ( T.F.C ). Reverse osmosis technology is an advanced water treatment technology. In order to produce drinking water that meets relevant drinking water standards, reverse osmosis technology is increasingly used in various countries. The World Health Organization (WHO) has formulated drinking water quality standards. Drinking water standards vary from country to country. Their formulation and implementation are often determined by the World Health Organization (WHO). * * Different departments are responsible. Taking the United States as an example, it is generally administered by the U.S. Environmental Protection Agency ( E.P.A ) is responsible for this work. The well-known U.S. Food and Drug Administration ( F.D.A ), is only responsible for the formulation and implementation of relevant standards for food and medicine, and is not responsible for drinking water. Although the U.S. Environmental Protection Agency ( E.P.A ) is responsible for drinking water, but so far, there is no official safety and reliability standard that can be used to evaluate reverse osmosis membranes. USA * * The Sanitation Foundation (NSF), a non-profit group in the United States, developed a standard in 1996 to evaluate drinking water reverse osmosis systems. According to the American Water Quality Association ( W.Q.A ) Recommended drinking water treatment technology, the reverse osmosis method can be used to remove turbidity, color, hardness, radioactive elements such as radium and uranium, carcinogens such as trihalomethanes and asbestos, and various inorganic ions in water, especially antimony, arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, selenium, aluminum, manganese, zinc, and other metal ions as well as cyanide, nitrite and other chemical substances that are harmful to the human body. (Return) How reverse osmosis works. Reverse osmosis technology uses semipermeable membranes ( R.O Membrane) uses water pressure (or pump pressure) to make water penetrate from the higher concentration side to the lower concentration side, using a pore size of only 1/10000um R.O The membrane (equivalent to 1/60000 of the size of E. coli and 1/3000 of the virus) can remove all industrial pollutants and heavy metals, bacteria, viruses and other impurities mixed into the water today. The conductivity is below 10us/cm (25 degrees), and the total dissolved solid content is less than 3mg/1 ； In order to achieve the prescribed physical and chemical indicators and hygienic standards, it can produce extremely clear and pure water, which is the best choice for the human body to replenish water in a timely manner. because R.O The purity of water produced by reverse osmosis technology is the highest among all water purification technologies currently mastered by mankind. The purity is almost 100%, so people call this water pure water. Selective adsorption capillary flow theory This theory believes that the semipermeable membrane has specific selective adsorption properties. It adsorbs water molecules and repels most solute molecules, so an adsorption layer composed purely of water molecules is formed on the surface of the membrane. It is generally believed that a semipermeable membrane has very small pores. Under the action of pressure (such as concentration driving force or water pressure), water molecules in the adsorption layer pass through the pores and migrate to the other side of the membrane, thus forming a permeable capillary flow movement. This theory also believes that the water permeability and solute repellency of the membrane are mainly related to the ratio of the membrane pore diameter and the thickness of the pure water adsorption layer. Assume that the thickness of the adsorption layer is t, the diameter of the membrane pore is d, and the ratio is m=d/t. When m is larger, the water permeability is greater and the repulsion to solutes is smaller. ； On the contrary, when m is smaller, the water permeability is smaller and the repellency to solute is greater. It is generally believed that d=2t is the critical state. At this time, the repulsion and water permeability are large, and it is most suitable for the separation of water and solute. This pore size is called the critical pore size. At the critical pore size, the reason why large water permeability and solute repellency can be obtained at the same time is explained as follows. The thickness of the pure water adsorption layer on the membrane surface is t, which means that the effective rejection range of the membrane to solutes is t. When the membrane pore is less than 2t, the entire membrane pore area is within the range, so the permeability of the solute is equal to zero. ； However, because the membrane pores are too small, the water permeability is not large. When d=2t, the rejection range of the membrane around the pores exactly intersects at the center of the pores, and the solute permeability is still equal to zero. However, because the membrane pores are larger than before, the water permeability also increases. When d>2t, the repulsive force of the membrane around the hole cannot reach the center of the hole, and a non-repulsive area appears near the center of the hole. The higher the ratio m is, the larger the area of ​​the non-rejection area is. The non-rejection region is the passage for solutes to pass through the membrane pores ； The larger the channel, the greater the solute permeability. Therefore, when d>2t, although the water permeability is good, the solute rejection rate will decrease. * * reduce. (Return) The Origin of Reverse Osmosis The osmosis phenomenon was discovered by French Abble Nellet in 1748, and the idea of ​​reverse osmosis was proposed by American Hassler in 1950. However, it was not until 1960 when American scientists Loeb and DR.S. Sourirajan successfully developed the first reverse osmosis membrane with high separation efficiency and high water permeability using CA that reverse osmosis membrane separation became a reality. It is said that the phenomenon of reverse osmosis was discovered by American scientist DR.S. Sourirajan in 1950 when he accidentally discovered that a seagull took a large mouthful of seawater from the sea surface while flying at sea, and spit out a small mouthful of seawater after a few seconds. This raised questions because animals that breathe through lungs on land are absolutely unable to drink high salt content. After dissection of seawater, it was found that there is a thin film in the seagull's body. The film is very precise. The seawater is inhaled into the body by the seagull and then pressurized. The water molecules are then penetrated through the membrane and converted into fresh water through the pressure. The seawater containing impurities and highly concentrated salt is spit out of the mouth. This is the reverse osmosis method (REVERSE). OSMOSIS abbreviation R.O ) the basic theoretical structure of ； In 1953, it was used in seawater desalination and salt removal equipment by the University of Florida. In 1960, it was approved by the US federal government. * * Project Support America U.C.L.A Dr. S. Sidney Lode, a professor at the University School of Medicine, collaborated with Dr. S. Sourirajan to start research on reverse osmosis membranes, investing approximately US$400 million a year in research, so that it can be used by astronauts, so that there is no need to carry a large amount of drinking water into space. It was not until 1960 that more and more scholars and experts were involved in research work, making their participation more sophisticated and solving the problem of human drinking water. No wonder Dr. Fritsh says: The research and invention of reverse osmosis membrane is a great contribution to mankind, and it is even worthy of winning the Nobel Prize. (Return) Application of reverse osmosis in water treatment Domestic reverse osmosis membranes and their applications my country began to develop reverse osmosis membranes in the mid-1960s, not far from the start time abroad. However, due to limitations of raw materials and basic industrial conditions, the performance of the membrane elements produced is low and the production cost is high, and large-scale production has not yet been achieved. In comparison, although the development of ultrafiltration and microfiltration membranes in my country started in the 1970s later than reverse osmosis, it has now developed to hundreds of production plants. Although there are problems such as a small number of varieties, insufficient quality and imperfect performance, the low price not only effectively blocks the large inflow of similar foreign products, but also expands the scope of application. Domestic reverse osmosis applications began in the late 1970s, and were initially limited to pure water for electronics and semiconductors. After the 1980s, they gradually expanded to electric power and other industries. Since the 1990s, they have become popular in drinking water treatment. Now reverse osmosis has entered pure drinking water for households. The past three years have been a period of great development for reverse osmosis applications. According to conservative estimates, domestic sales of various reverse osmosis membrane components in 1997 were around RMB 100-150 million. As several domestic advanced production lines are put into operation one after another, it is expected that the market share of domestically produced reverse osmosis membranes will increase in the future. Looking at the domestic reverse osmosis application market, there are the following characteristics:: 1. Large-scale reverse osmosis devices are concentrated in boiler feed water. According to incomplete statistics, there are more than 50 reverse osmosis devices with a capacity of more than 100 tons/hour that have been built or under construction in my country. However, except for a few electronics and other industries, most of them are focused on boiler feed water. It was first a thermal power plant, and later expanded to oil refining, petrochemical, fertilizer, chemical and other industries. The largest scale is 600 tons/hour, and it is estimated that ultra-large reverse osmosis devices exceeding 1,000 tons/hour will appear within this century. China has accumulated rich experience in design, construction and operation in this field. Currently, there are more than 10 domestic water treatment engineering companies that have built reverse osmosis devices with a scale of more than 100 tons/hour. 2. Drinking water treatment applications are limited to medium and small scales. In foreign countries, ultra-large reverse osmosis or nanofiltration devices with a scale of 1,000 to 10,000 tons/hour are mostly used in urban water supply systems. However, domestic reverse osmosis devices for drinking water are still medium and small scales of less than tens of tons/hour. With the development of economy and the popularization of membrane technology, the application prospects in this field are great. 3 Oilfield water and wastewater treatment applications have yet to be developed. Due to the high technical difficulty and economic cost of application in this field, the country is still in the research and development stage. With the development of the petroleum industry and the increasing calls for water reuse and environmental protection, it is not too far away that membrane technology will enter this field in large quantities. It is also an excellent business opportunity for membrane manufacturers and engineering companies. 4 The application of nanofiltration membranes has just begun. Although the advantages of nanofiltration membranes in the fields of drinking water purification treatment, sewage and wastewater discharge treatment, and concentration and refining of various aqueous solutions have gradually been recognized by people, due to high membrane costs and lack of application experience, this field has just started in China, and it is expected to have great development in the future. Foreign reverse osmosis and its applications. The United States is the inventor and largest producer of reverse osmosis membrane technology. However, Japan, as a rising star, has begun to catch up with and surpass the United States in its research and development capabilities. For example, the ES20 series of ultra-low pressure membranes launched by Nitto Denko in 1996 represents the highest level of reverse osmosis membranes today. It has achieved a desalination rate of 99.7% under a pressure of 0.75Mpa and a water production rate of 0.8 tons/square meter per day. The LF10 series of pollution-resistant low-pressure reverse osmosis membranes produced by the company in 1997 showed a new direction in reverse osmosis membrane development. This membrane is compounded with a layer of polyvinyl alcohol on the surface of the traditional aromatic polyamide membrane, which not only eliminates the negative charge on the membrane surface but also improves the hydrophilicity and chlorine resistance of the membrane, thus * * Improves the anti-pollution performance of the reverse osmosis membrane. At present, the major foreign manufacturers of reverse osmosis membranes are American and Japanese companies, among which Dupont and Oyobo monopolize the world market for hollow fiber reverse osmosis membranes. There are 7 major manufacturers of rolled reverse osmosis membranes. They are: American Hydranautics Company, which became a wholly-owned subsidiary of Japan's Nitto Corporation in 1987 Japan's Nitto Denko Group American Filmtec Company, which became a wholly-owned subsidiary of American Dow Chemcal (Dow Chemical) Company in 1985 American Fluid system company, which is now a subsidiary of the American KOCH Company. The Japanese Toray Company (Toray) and the American Desel Company, which is now a subsidiary of the American Osmonics Company. The American Trisep Company is used for reverse osmosis in the United States and Europe. It is mainly used for various industrial water and drinking water. ； There are many applications of seawater desalination in the Middle East and Spain ； Japan is mainly used for semiconductors and electronics ； In addition to semiconductors and electronics, South Korea and Taiwan have a huge demand for small drinking pure water. The following introduces the application of membrane separation for drinking water in the United States.: In addition to the extensive use of medium, small and household reverse osmosis systems in the United States, there are also many large public water supply systems. In September 1996, the National Research Institute of the United States conducted a questionnaire survey to collect statistics on the status of large-scale drinking water desalination devices in the United States. The survey published data on 179 desalinated water plants used for drinking water purposes in 21 of the 50 U.S. states. The results show that the total water production capacity of these devices is 1.4 million tons/day, and the proportions of various desalination methods in the total water production capacity of the devices are respectively: Land water (brackish water) reverse osmosis 47%, nanofiltration membrane softening 31%, reversible electrodialysis 13%, seawater desalination 8%. It is worth noting that nanofiltration membrane softening has the fastest growth rate. In the four years from 1992 to 1996, nanofiltration membrane softening devices increased by 500%. * * higher than other methods. This is because nanofiltration membranes can not only soften and moderately desalinate water sources at low pressure, but also remove trihalomethane generation energy (THMFP), color, bacteria, viruses and dissolved organic matter, so they are becoming increasingly popular. The survey also provides a statistical comparison of the economic costs of various desalination methods. The results are shown in Table 1. Whether it is a primary equipment investment or operation and maintenance costs, nanofiltration membrane softening is the lowest. Ion exchange method The ion exchange method uses a spherical resin (ion exchange resin) to filter raw water, and the ions in the water will exchange with the ions fixed on the resin. The two common ion exchange methods are hard water softening and deionization. Hard water softening is mainly used as a pre-treatment procedure to reduce the hardness of water before reverse osmosis (RO) treatment. The spherical resin in the softener softens the water by exchanging two sodium ions for one calcium ion or magnesium ion. Ion exchange resins use hydrogen ions to exchange cations and hydroxyl ions to exchange anions; cation exchange resins made of styrene and divinylbenzene containing sulfonates will use hydrogen ions to exchange various cations encountered (such as Na+, Ca2+, Al3+). Similarly, anion exchange resins made from styrene containing quaternary ammonium salts will exchange various anions (such as Cl-) encountered with hydroxyl ions. The hydrogen ions released from the cation exchange resin combine with the hydroxide ions released from the anion exchange resin to produce pure water. Anion and cation exchange resins can be packaged in different ion exchange beds respectively, divided into so-called anion exchange beds and cation exchange beds. Cation exchange resins and anion exchange resins can also be mixed together and placed in the same ion exchange bed. Regardless of which form, When the resin and the charged impurities in the water have exchanged the hydrogen ions and/or hydroxyl ions on the resin, it must be "regenerated". The regeneration procedure is exactly the opposite of the purification procedure. Hydrogen ions and hydroxyl ions are used to regenerate and exchange impurities attached to the ion exchange resin. If the ion exchange method is combined with other water purification methods (such as reverse osmosis, filtration and activated carbon adsorption), the ion exchange method will play a very important part in the entire purification system. The ion exchange method can effectively remove ions, but cannot effectively remove most organic matter or microorganisms. Microorganisms can attach to the resin and use the resin as a culture medium, allowing the microorganisms to grow rapidly and generate heat sources. Therefore, it needs to be designed and used in conjunction with other purification methods. The organic matter in the activated carbon adsorption method may be cationic, anionic or nonionic substances. The ion exchange resin can remove some soluble organic acids and organic bases (anions and cations) in the raw water, but some nonionic organic matter will be coated by the resin. This process is called the "contamination blocking" phenomenon of the resin, which will not only reduce the life of the resin, but also reduce its exchange capacity. To protect the ion exchange resin, an activated carbon filter can be installed in front of the ion exchange resin to remove nonionic organic matter. The adsorption process of activated carbon is achieved by utilizing the pore size of the activated carbon filter and the permeability of organic matter through the pores. The adsorption rate is related to the molecular weight and molecular size of organic matter. Some granular activated carbon is more effective in removing chloramines. Activated carbon can also remove free chlorine in water to protect other purification units that are sensitive to oxidants in the pure water system. Activated carbon is usually used in combination with other treatment methods. When designing a pure water system, the configuration of activated carbon and other related purification units is an extremely important project. Micropore filtration method Micropore filtration method includes three types: depth filtration (depth), screen filtration (screen) and surface filtration (surface). Depth filter membrane is a matrix made of woven fibers or compressed materials, which uses random adsorption or capture to retain particles. Screen filter membrane is basically It has a consistent structure, just like a sieve, which retains particles larger than the pore size on the surface (the pore size of this filter membrane is very precise), while surface filtration is a multi-layer structure. When the solution passes through the filter membrane, particles larger than the pores inside the filter membrane will be retained and mainly accumulated on the surface of the filter membrane. Since the above three types of filter membranes have different functions, it is very important to distinguish between them. Since depth filtration is a more economical method that can remove more than 98% of suspended solids while protecting the downstream purification unit from being damaged or blocked, it is usually used as a pre-filtration treatment. Surface filtration can remove more than 99.99% of suspended solids, so it is also It can be used as a pre-filtration treatment or clarification. Microporous membranes (screen filters) are generally placed at the final point of use in the purification system to remove the last remaining trace resin fragments, carbon dust, colloidal particles and microorganisms. For example: 0.22μm microporous filter membrane, which can filter all bacteria and is usually used to sterilize intravenous fluids, serum and antibiotics. The ultrafiltration microporous membrane removes particles based on its pore size, while the ultrafiltration (UF) membrane is a molecular sieve that uses size as a basis to allow the solution to pass through an extremely fine filter membrane to achieve the purpose of separating molecules of different sizes in the solution. Ultrafiltration membrane is a strong, thin, selective permeable membrane that can intercept most molecules above a certain size, including colloids, microorganisms and heat sources. Smaller molecules, such as water and ions, can pass through the filter membrane. Therefore, ultrafiltration can concentrate the macromolecules in the retentate, but some macromolecules will still leak into the filtrate. There are several different ranges of ultrafiltration membranes. In all cases, ultrafiltration membranes will intercept most molecules that are larger than the molecular weight defined by their molecular sieve. Reverse osmosis (RO) method is the most economical method to achieve an impurity removal rate of 90% to 99%. The pore structure of the RO membrane is denser than that of the UF membrane. The RO membrane can remove all particles, bacteria and organic matter with a molecular weight greater than 300 (including heat sources). Osmosis occurs naturally when two solutions of different concentrations are separated by a semipermeable membrane. The osmotic pressure presses water through the semipermeable membrane, and the water dilutes the solution with a higher concentration, finally causing a concentration balance. In a water purification system, pressure is applied to a solution with a high concentration. In the liquid, to counteract the osmotic pressure. This forces the pure water from the high-concentration liquid to pass through the RO membrane and can be collected. Because the RO membrane is extremely dense, the water flow produced is very slow, and it will take a considerable amount of time before there is enough water in the water storage tank. The RO membrane can perform ion exclusion, so that only water can pass through the RO membrane, and all other ions and dissolved molecules are intercepted and excluded (including salts and sugars). The RO membrane excludes ions through a charge reaction. The greater the charge, the higher the exclusion, so the RO membrane can exclude almost all ions. (>99%) strong ionic high-valent ions, but the effect on weakly ionic monovalent ions (such as sodium ions) is only 95%. Different incoming water requires different types of RO membranes. RO membranes include made of cellulose acetate, or a mixed thin-layer polymer based on polythiamine and polysulfone matrix. Based on the raw water quality and produced water quality, after proper design, RO is the most economical and effective method to purify tap water. RO is also the best pre-treatment method for reagent-grade pure water systems. Ultraviolet irradiation method Ultraviolet irradiation method has been widely used in water treatment. The 254nm ultraviolet rays emitted by low-pressure mercury lamps are an effective sterilization method, because the DNA and proteins in bacteria will absorb ultraviolet rays and cause death. Recent advances in UV lamp manufacturing technology have made it possible to manufacture UV lamps that produce both 185nm and 254nm wavelengths. This combination of light wavelengths can use light to oxidize organic compounds. This special lamp can then reduce the total organic carbon concentration in pure water to less than 5ppb. This post was last edited by johncom on 2009-3-4 13:30 ]

I think the principles of ion exchange and RO are easy to find or search. Scope of application: Ion exchange is suitable for water with better water quality and lower salt content, and RO is suitable for water with poor water quality. Specific choices require feasibility and economic analysis.

If the requirements for water are higher, ion exchange can be connected in series later to prepare high-purity water.

Principle of Ion Exchange Ion exchange resin is a polymer with corresponding functional groups. In general, conventional sodium ion exchange resins contain a large amount of sodium ions. When the content of calcium and magnesium ions in the water is high, the ion exchange resin can release sodium ions, and the functional groups combine with the calcium and magnesium ions, so that the content of calcium and magnesium ions in the water decreases and the hardness of the water decreases. Hard water becomes soft water, which is the working process of water softening equipment. When a large number of functional groups on the resin combine with calcium and magnesium ions, the softening ability of the resin decreases. You can use sodium chloride solution to flow through the resin. At this time, the sodium ion content in the solution is high, and the functional groups will release calcium and magnesium ions and combine with sodium ions. In this way, the exchange capacity of the resin is restored. This process is called "regeneration". Due to actual work needs, the standard workflow of softened water equipment mainly includes: There are five processes: working (sometimes called water production, the same below), backwashing, salt absorption (regeneration), slow flushing (replacement), and fast flushing. All processes of different softened water equipment are very similar, but due to differences in actual processes or control needs, there may be some additional processes. Any softened water equipment based on sodium ion exchange is developed on the basis of these five processes (among them, fully automatic softened water equipment will add a brine re-injection process).  Backwash: After the equipment has been working for a period of time, a lot of dirt brought by the raw water will be intercepted on the upper part of the resin. Only after these dirt are removed can the ion exchange resin be fully exposed and the regeneration effect can be guaranteed. The backwash process is that water washes in from the bottom of the resin and flows out from the top, so that the dirt intercepted at the top can be washed away. This process usually takes about 5-15 minutes.  Salt absorption (regeneration): In the process of injecting salt water into the resin tank, traditional equipment uses a salt pump to inject the salt water, while fully automatic equipment uses a dedicated built-in ejector to inhale the salt water (as long as the incoming water has a certain pressure). In the actual working process, the regeneration effect of salt water flowing through the resin at a slower speed is better than that of simply soaking the resin with salt water. Therefore, softened water equipment is regenerated by the slow flow of salt water through the resin. This process generally takes about 30 minutes, and the actual time is affected by the amount of salt used.  Slow flush (replacement): After using brine to flow through the resin, the process of slowly rinsing all the salts in the resin with raw water at the same flow rate is called slow rinsing. Since there are still a large number of calcium and magnesium ions on the functional groups that are exchanged with sodium ions during this rinsing process, according to actual experience, this process is the main process of regeneration, so many people call this process replacement. This process generally takes the same time as inhaling salt, which is about 30 minutes. Quick rinse: In order to completely rinse away the residual salt, use raw water to rinse the resin with a flow rate close to the actual work. The final water output of this process should be soft water that meets the standard. Generally, the quick rinse process takes 5-15 minutes.   Application 1) Water treatment There is a huge demand for ion exchange resins in the field of water treatment, accounting for about 90% of the production of ion exchange resins. They are used for the removal of various anions and cations in water. At present, the largest consumption of ion exchange resin is used in pure water treatment in thermal power plants, followed by atomic energy, semiconductor, electronic industries, etc.  2) Food industry ion exchange resin can be used in industrial equipment such as sugar refining, monosodium glutamate, alcohol refining, and biological products. For example: High fructose corn syrup is produced by extracting starch from corn, then hydrolyzing it to produce glucose and fructose, and then undergoing ion exchange treatment to produce high fructose corn syrup. The consumption of ion exchange resins in the food industry is second only to water treatment.  3) Pharmaceutical industry Pharmaceutical industry ion exchange resin plays an important role in developing a new generation of antibiotics and improving the quality of original antibiotics. The successful development of streptomycin is a prominent example. In recent years, research has also been conducted on traditional Chinese medicine commissions and other aspects.  4) In the synthetic chemistry and petrochemical industries, acids and bases are commonly used as catalysts in organic synthesis to carry out reactions such as esterification, hydrolysis, transesterification, and hydration. Using ion exchange resin instead of inorganic acids and bases can also carry out the above reactions and has more advantages. For example, the resin can be used repeatedly, the product is easy to separate, the reactor will not be corroded, the environment will not be polluted, and the reaction is easy to control. The preparation of methyl tert-butyl ether (MTBE) is to use macroporous ion exchange resin as a catalyst, which is formed by the reaction of isobutylene and methanol, replacing the original tetraethyl lead, which can cause serious pollution to the environment.  5) Environmental protection ion exchange resin has been used in many environmental protection issues of great concern. Currently, many aqueous or non-aqueous solutions contain toxic ionic or non-ionic substances, which can be recycled with resin. Such as removing metal ions from electroplating waste liquid, recycling useful substances from film production waste liquid, etc.  6) Hydrometallurgy and other ion exchange resins can separate, concentrate, purify uranium and extract rare earth elements and precious metals from depleted uranium ores.  Nowadays, ion exchange is the most mature technology, but it is not environmentally friendly, discharges acid and alkali wastewater, and wastes water resources.   Principle of Reverse Osmosis Reverse osmosis is a new membrane separation technology developed in the 1960s. It is a process that relies on a reverse osmosis membrane to separate solvent and solute in a solution under pressure. To understand the principle of reverse osmosis desalination, you must first understand the concept of "osmosis". Osmosis is a physical phenomenon. When two waters containing different concentrations of salts are separated by a semi-permeable membrane, you will find that the water on the side with less salt content will penetrate through the membrane into the water with high salt content, but the salt content will not penetrate. In this way, the salt concentrations on both sides will gradually blend until they are equal. However, it takes a long time to complete this process, which is also called natural penetration. However, if you try to add a pressure on the water side with high salt content, the result can also stop the above infiltration. The pressure at this time is called osmotic pressure. If the pressure is increased, water can be caused to penetrate in the opposite direction, and the salt remains. Therefore, the principle of reverse osmosis desalination is to apply a pressure greater than the natural osmotic pressure in salty water (such as raw water) to cause osmosis to proceed in the opposite direction, forcing the water molecules in the raw water to the other side of the membrane and turning it into clean water, thus achieving the purpose of removing salt from the water. This is the principle of reverse osmosis desalination. At present, reverse osmosis membranes are mainly divided into two categories: cellulose membranes and non-cellulose membranes based on the chemical composition of their membrane materials. According to the physical structure of membrane materials, they can be roughly divided into asymmetric membranes and composite membranes. The most widely used cellulose membrane is cellulose acetate membrane (CA membrane for short). The total thickness of the membrane is about 100 μm, and the thickness of the entire epidermal layer is about 0.25 μm. The epidermal layer is covered with micropores, with a pore diameter of about 5 to 10 angstroms, so it can filter out extremely fine particles. The pores in the porous support layer are very large, about several thousand angstroms, so the membrane with this asymmetric structure is also called an asymmetric membrane. In reverse osmosis operation, the cellulose acetate membrane can achieve the expected desalination effect only when the epidermal layer is in contact with high-pressure raw water and must not be inverted. The main types of non-cellulosic membranes are aromatic polyamides, and others include polyaniscaramide membranes, benzotriene membranes, polysulfone amide membranes, polytetrafluoroethylene graft membranes, polyethylene imine membranes, etc. The polyamide composite membrane developed in recent years is made of a layer of polyester non-woven fabric as a supporting layer. Since the polyester non-woven fabric is very irregular and too loose, it is not suitable as the bottom layer of the salt barrier layer. Therefore, the microporous engineering plastic polysulfone is cast on the surface of the non-woven fabric. The pores on the surface of the poly maple layer are controlled to be approximately 150 Angstroms. The barrier layer is made of a highly cross-linked aromatic polyamide with a thickness of approximately 2000 Angstroms. Highly cross-linked aromatic polyamide is polymerized by trimellitic acid chloride and phenylenediamine. Because this kind of membrane is composed of three layers of different materials, it is called a composite membrane. Reverse osmosis membranes are generally cleaned once every six months to a year. They have high water quality requirements and require pretreatment. It is generally used to make pure water for boilers and is rarely used to treat sewage. Reverse osmosis is a relatively mature and advanced water treatment process today. It is water-saving and environmentally friendly. It would be better if the concentrated water can be utilized.

  The acid and alkali of ion exchange pollute the environment, but how to deal with the concentrated brine discharged from RO? No emissions allowed!

Ion exchange will have more and more uses in the future. Membrane application technology is already very mature. Ion exchange is selective and is widely used in sugar and medicine. There is also a lot of information on membranes.

RO has been widely used in water treatment. Specifically, it is widely used in seawater desalination and brackish water desalination. The advantages are obvious, the equipment is highly integrated and the operating costs are low. Ion exchange is mainly used to prepare high-purity water or to soften the system. The equipment investment is not large, but the operation is cumbersome.

Ion exchange is mainly used for seawater desalination, hard water softening and the treatment of industrial wastewater containing heavy metals. The principle is to use the sodium ions of the ion exchange resin to replace the metal ions in the water through ion replacement, and then perform a replacement reaction between the saturated ion exchange resin and the sodium chloride solution, that is, the regeneration of the resin. Operating conditions will affect the removal rate, including flow rate, resin regeneration solution concentration and regeneration flow rate. Generally at low operating flow rates, the longer the wastewater is in contact with the resin, the higher the removal rate. Among them, resin selection, pH value, internal solution concentration, and resin dosage will all affect the effect of ion exchange method on water treatment.

In the use of pure water, direct desalination by ion exchange is becoming less and less. Most of the salts are removed by reverse osmosis, and ion exchange is used for refining.

I think it has been made very clear above. I just want to add something.: Generally speaking, if the conductivity of raw water is not high, such as less than 300, or even 100, it is more economical to use ion exchange. Higher than 300, then reverse osmosis is more economical

The ion-exchanged water goes into the sewage plant for treatment, and the concentrated water produced by RO goes into the fire pool, and then into the entire fire water system through the fire water pump. It can be used for cleaning at various positions, flushing toilets, spraying lawns, spraying roads in summer, etc.

The operation cost of ion exchange with salt content below 500mg/L is cheaper than reverse osmosis, but now the salt content requirement for full chamber bed is 800mg/L.

Are you annoyed? What you said is a bit RO.

To be fair, the advantages and disadvantages you mentioned are all about reverse osmosis.