What is RO Water Treatment Technology

• by John Lau.
• Last updated 12月 6, 2020

Reverse osmosis (RO) is the synonym of reverse osmosis, which is a kind of reverse migration movement of osmosis, a separation method to separate solutes and solvents in solution by the selective retention of semi-permeable membranes under pressure drive, with a pore size of about 5-10A. reverse osmosis, also known as reverse osmosis, is a kind of membrane separation operation to separate solvents from solutions with the driving force of pressure difference. It is called reverse osmosis because it is opposite to the direction of natural osmosis. According to the different osmotic pressures of various materials, reverse osmosis pressure greater than the osmotic pressure can be used, i.e., reverse osmosis method, to achieve the purpose of separation, extraction, purification and concentration. It has been widely used in the purification and concentration of various liquids, and is one of the most advanced and energy-saving effective separation technologies today. One of the most common application examples is applied to water treatment process, with reverse osmosis technology can be inorganic ions, bacteria, viruses, organic and colloidal impurities in the raw water to remove in order to obtain high quality pure water, with low energy consumption, no pollution, advanced technology, easy operation and other advantages. At present, the most widely used is the rolled polyamide composite membrane, the water flux and removal rate will be affected by pressure, temperature, recovery, feed water salinity and PH value.

01. Video On How RO Works

02. History Of Water Treatment

The invention and large-scale application of Reverse Osmosis (RO) is a landmark achievement in the development of modern water treatment technology. As an advanced membrane separation technology developed since the 1950s, RO has been widely used in desalination, desalination of brackish water, domestic water purification and wastewater reuse, etc. In 2018, more than 11 billion tons of desalinated water has been produced globally using RO technology, which can be used by 320 million people. Over the past 70 years, many important scientists, entrepreneurs and a large number of technology companies have joined forces to perform a fascinating development of reverse osmosis technology.

Proof Of Concept

• As the name implies, reverse osmosis, as opposed to Osmosis, refers to the reverse process of the osmosis phenomenon. At the heart of both osmosis and reverse osmosis processes is a semi-permeable membrane. The so-called semi-permeable membrane simply means that water is permeable, while salts or other solutes dissolved in water are not. If the concentration of solutes in solution on both sides of a semi-permeable membrane is inconsistent, water molecules will spontaneously pass through the membrane from the low concentration side to the high concentration side, until the solution concentration on both sides of the membrane is consistent, or a certain net pressure difference is established on the low concentration side of the membrane due to the elevated water level and other reasons. This is the phenomenon of osmosis, and this net pressure difference is the osmotic pressure.
• We know that doctors often use saline solution, which is an aqueous solution of sodium chloride at a concentration of 0.9%, when administering fluids to patients. This concentration is comparable to the concentration of human body fluids, so the infusion will not harm the body by causing significant osmosis on either side of the cell membrane. Although osmosis occurs every day in our bodies, it was not until 1748 that it was first scientifically discovered by French physicist Jean-Antoine Nollet, who was a great lover of science.
• Nollet, a great lover of science, is said to have demonstrated the Leiden bottle discharge experiment to Louis XV. In 1886, a Dutch scientist, summarizing the experimental data, came up with the osmolarity calculation company for dilute solutions. If you’ve studied physical chemistry, you may remember that this man’s name was Van’t Hoff.
• In the 1950s, the Kennedy administration began to look to desalination as a solution to water shortages in some arid regions of the U.S. and to the national problem of overuse of groundwater, and in 1952, Congress passed the Saline Water Conversion Act, and in 1953, it began to fund research into desalination technology, although in that year, it was not until 1953 that the Kennedy administration began to fund desalination. In 1955, the U.S. Department of the Interior created the Office of Saline Water (OSW) to coordinate research on various desalination technologies, and in 1970, OSW’s annual funding had increased to about $26 million.
• In 1949, Gerald Hassler and others at the University of California, Los Angeles (UCLA) initiated the first research on membrane desalination, and in 1950, Hassler described the “Salt Repelling Permeable Membrane” in an internal UCLA report. In August 1956, Hassler first coined the term “Reverse Osmosis” in another UCLA internal report.
• Around 1954, Professor Charles Reid’s team at the University of Florida, funded by OSW, also began researching desalination permeable membranes. They evaluated many commercially available membranes and found that cellulose acetate membranes had good semi-permeability, salt retention greater than 99%, and a water permeability coefficient of 0.00012m3/m2-d-atm. Although the membrane permeability was more than two orders of magnitude lower than that of modern commercial membranes and had no commercial value, they experimentally verified for the first time the pressure-driven desalination of reverse osmosis membranes using synthetic membranes. In April 1957, Reed and his colleague E. J. Breton used the term “RO” in a report to OSW.
• Interestingly, at a time when there was no Internet and no circle of friends, although both universities were working on desalination membranes, they had no knowledge of each other until November 1957, when they met at a symposium organized by OSW.
• The next question was, how can the water permeability of membranes be dramatically improved in order to gain practical value?

Membrane Technology Breakthrough

• In 1956, in addition to Hassler’s group, Professor Samuel Yuster’s group at UCLA was also conducting research on membrane desalination funded by OSW. 33-year-old Srinivasa Sourirajan, a scientist of Indian descent, was the first to participate in this research. In the summer of 1958, 41-year-old Sidney Loeb, a scientist of Jewish descent, joined the group.
• Solilakin and Loeb’s first work was also to screen commercial thin films. In the process, they discovered that a commercial cellulose acetate ultrafiltration membrane could be made to have certain desalination properties by heat-treating it. They also discovered, unexpectedly, that the orientation of the membrane during testing was critical, with one side facing the feed solution significantly better than the other.
• The heat-treated cellulose acetate membranes achieved a salt retention rate of 92% and a water permeability coefficient of 0.00095m3/m2-d-atm, much higher than the other membranes. More importantly, they thus realized that asymmetry in membrane structure has a significant impact on membrane performance, and that reducing the effective thickness of the membrane is the key. To further improve membrane performance, the two scientists decided to make their own membranes.
• In 1959, Lobe and Solilakin, through a series of exploration, used four raw materials, cellulose acetate – acetone – water – magnesium perchlorate, with a ratio of 22.2: 66.7: 10.0: 1.1 to prepare membrane casting liquid, and through the optimization of temperature, evaporation time, heat treatment and other factors, the first time to prepare a synthetic reverse osmosis membrane with asymmetric structure. The so-called asymmetric structure simply means that a membrane is composed of two parts, a support layer and a separation layer, with the support layer being loose in structure and the separation layer being dense in structure. This membrane was later called an L-S membrane.
• The asymmetric membranes of Lobe and Sorilakin have a salt retention rate of 99% and a water permeability coefficient of 0.0048 m3/m2-d-atm, which is 5 times that of ultrafiltration heat-treated membranes and almost in the same order of magnitude as modern commercial reverse osmosis membranes. The membranes also have good mechanical stability. This breakthrough provided the most important technical foundation for reverse osmosis technology to eventually move towards large-scale engineering applications. Since then, reverse osmosis membrane technology has entered a period of rapid development and is gradually moving toward commercial applications.
• In 1965, the world’s first commercial reverse osmosis plant was built in the small town of Coalinga, California, under Lobe’s direction, producing 5,000 gallons of water per day. This marked the realization of mankind’s dream of producing drinking water from seawater on a large scale and at an acceptable cost. Soon, new pilot lines appeared at various locations in California, fueling the rapid progress of the technology.
• Given their legendary status in the field of reverse osmosis membranes, Lobe and Soliragin have a few more personal stories to tell.
• Let’s start with Lobe. Born in Kansas, Lobe was 41 years old when he joined UCLA for his PhD in 1958. In 1966, perhaps as a way out of his heartbreak, Lobe accepted an offer to work on a project in Israel for nine months.
• In 2005, Lobe was invited to attend the opening of a 300,000-tonne-per-day reverse osmosis desalination plant in Ashkelon, Israel, to witness his invention firsthand. To benefit the world in a magnificent way. Lobe passed away in 2008 at the age of 91.
• Soliragin
• And then there was Soliragin. Born in India in 1923, seven years younger than Lobo, he received his Ph.D. from the Institute of Science, Bangalore, India, in 1953, went to Yale University to work in the chemical engineering department in 1954, worked at UCLA from 1956 to 1961, went to the National Research Council of Canada as a research assistant in 1961, became a senior researcher in 1967, and was promoted to first class in 1976. Research Fellow. Soliragin has been active in the field of membrane technology for a long time, and was first lectured in China in 1983.

Successful Commercialization

• The birth of L-S membranes has brought light to the industrial application of reverse osmosis technology. However, it became clear that a critical engineering problem needed to be solved before the technology could be commercialized, and that was the design of the membrane module.
• The L-S membrane invented by Loeb and Soliragin in 1959 was a flat-plate membrane, so early membrane modules borrowed directly from the plate and frame construction of industrial filtration equipment. Lobe and others later developed tubular reverse osmosis (RO) membranes with diameters ranging from 1-3 cm, which were used in the Coringa plant. However, both the plate and tube types suffered from complex assembly and small membrane area per unit volume, and thus failed to develop into the dominant form of commercial reverse osmosis membrane module.
• Around 1965, Dow Chemical and DuPont both invested in the development of hollow fiber reverse osmosis membranes, probably because of their familiarity with the textile industry.
• In 1966, H. I. Mahon of Dow Chemical designed the first hollow fiber membrane spinning system, developed hollow fiber reverse osmosis membranes based on cellulose triacetate, and applied for the first patent (US3228877). They used concentric capillary spinnerets with an outer bore diameter of 400 microns, an inner bore diameter of 200 microns, and an inner bore diameter of 100 microns.
• In 1971, DuPont applied for a patent for hollow fiber reverse osmosis membrane modules based on polyamide (US3567632), and in 1979, another company with a textile background was also developing hollow fiber reverse osmosis membrane modules, Toyobo.
• Hollow fiber reverse osmosis membrane modules had a high loading density, but did not eventually become the mainstream of reverse osmosis membrane modules because of their very fine filament diameter and uncontrolled hydrodynamic state, which made them prone to fouling. This is what prompted Dow to switch to roll-on membranes. Toyobo is the only manufacturer that still maintains a line of cellulose acetate hollow fiber reverse osmosis membranes.
• If 1959 was the year that reverse osmosis achieved its technological milestone, 1963 was the year that the seeds of its commercial success were sown.
• In 1963, the North Star Research Institute in Minneapolis, Minnesota, also funded OSW research on desalination technology, and in 1967, John E. Cadotte of the North Star Research Institute invented the microporous polysulfone support. membranes. In the following years, he developed a variety of non-cellulose acetate composite membranes. But his passion for reverse osmosis was not limited to research.
• In 1977, Cadotte co-founded FilmTec, Inc. and in 1979, Cadotte filed the world’s first patent for reverse osmosis membranes prepared by interfacial polymerization (US 4277344). Interfacial polymerization allows the support and separation layers of reverse osmosis membranes to be optimized separately during the preparation process, thus further enhancing the membrane performance, which is known as thin layer composite (TFC) membranes. Interfacial polymerization has also become the standard preparation process for modern commercially available reverse osmosis membranes.
• In 1985, after abandoning hollow fiber reverse osmosis membranes, Dow Chemical acquired FilmTec Corporation. This was the origin of the famous Dow membranes. In 2017, Dow Chemical and DuPont merged their hollow fiber reverse osmosis membranes.
• It was also around 1963 that Donald T. Bray, a 41-year-old World War II veteran, began working on reverse osmosis membranes. In 1965, Bray filed the world’s first patent (US 3417870) for a multi-die rolled reverse osmosis membrane module, laying the groundwork for what is now General Atomics’ rolled reverse osmosis membrane module.
• General Atomics’ reverse osmosis membrane business evolved into Fluid Systems, and in 1998, Fluid Systems was acquired by Koch Membrane Systems, which is where Koch Membranes came from.
• In 1967, he left General Atomics and founded Desalination Systems. Desalination Systems did extensive work on diaphragm production and membrane module winding machines, and became a well-known producer of reverse osmosis membranes, including nanofiltration membranes with a unique multilayer structure.
• Also in 1963, Dean Spatz, a sophomore at Dartmouth College, was working on a project for his engineering class. They needed to design a suitable treatment for the poor drinking water available to South Dakota residents, and he decided to use the newly available reverse osmosis technology and successfully built a prototype.
• Spatz became interested in reverse osmosis technology and made it the subject of his undergraduate and master’s thesis, which was funded by OSW in 1965. During his master’s research, Spaatz is said to have enlisted Solilakin as a consultant.
• In 1968, after completing his master’s degree, Spatz joined a Miami-based company and was sent to Minneapolis to develop a reverse osmosis business, and in 1969, when the promised funds were not forthcoming, Spatz formed his own company. This was the birth of Osmonics.
• In 1996, at the age of 84, Bray sold Desalination Systems to Osmonics, and in 2002, GE bought Osmonics for $250 million, which is how GE Membranes came to be known. In 2017, GE’s reverse osmosis membrane business was sold in its entirety to SUEZ Water for $3.4 billion, along with GE Water Treatment.
• Also in 1963, Hydranautics, a company that would become a major name in reverse osmosis membranes, was founded in California, U.S. In 1970, Hydranautics officially entered the reverse osmosis membrane business. In 1987, Hydranautics was acquired by Nitto Denko, a Japanese company.
• Toray began researching cellulose acetate reverse osmosis (RO) membranes in 1968, its first low-pressure RO membranes were launched in 1978, its seawater RO membrane elements were launched in 1991, and its Blue Star Toray (TBMC) joint venture was established in Beijing in 2009.
• In addition to these long-established manufacturers from the 1960s or 1970s, a new wave of reverse osmosis membranes has emerged one after another.
• In 1990, a subsidiary of Korea’s Samsung Group began researching reverse osmosis membrane technology, and in 1995, it began exporting household RO membranes; in 1997, the company changed its name to Saehan Group, and in 2001, its high desalination rate desalination membranes went on the market; in 2008, Saehan Group changed its name to Woongjin Chemical Co. (Chemical). In early 2020, Toray acquired a 56.2% stake in Kumazin Chemical, whose reverse osmosis membrane products are commonly known as Seokhan membranes.
• In 2005, NanoH2O was founded in Los Angeles, California, with the claim of improving the performance of reverse osmosis membranes with nanotechnology, and in 2014, LG Chem acquired NanoH2O for $200 million, and the company has been stepping into the ranks of mainstream RO membrane suppliers in recent years.
• By now, some of the best-known international reverse osmosis membrane manufacturers have made their presence felt. According to Global Water Intelligence (GWI), during 2012-2017, 76% of RO membranes in large reverse osmosis systems of more than 50,000 tons/day came from four suppliers, including Toray, Dow, Hydranergy and LG Chem, accounting for 28%, 21%, 17% and 10% respectively.

Reverse Osmosis Technology In China

• From the above, we can see that the last century 60, 70’s is the foreign reverse osmosis key technology intensive breakthrough period. And our country was weak research foundation, and in a special historical period, so the same period of reverse osmosis technology research significantly behind. But through timely technology introduction and independent research and development, we have accumulated a wealth of application experience and preliminary technical achievements, laying an extremely important technical and personnel foundation for the overall progress of China’s reverse osmosis membrane technology and even water treatment technology.
• In 1966, the chemistry department of Shandong Ocean University, the State Oceanic Administration, the Chinese Academy of Sciences, Qingdao Institute of Oceanography, the Chinese Academy of Sciences Institute of Chemistry and other units began to study reverse osmosis technology, the development of asymmetric cellulose acetate membranes. 1967, the State Science and Technology Commission and the State Oceanic Administration organized a national desalination war, Qingdao and Beijing, mainly to carry out research on reverse osmosis. In 1975, the Bureau and other units developed a 1.7-ton disc type cellulose acetate reverse osmosis plant with daily production of fresh water. Bureau of Oceanography two desalination research laboratory gradually developed into today’s Hangzhou water treatment technology center.
• In 1974, they developed a 10-ton daily output cellulose acetate cased reverse osmosis plant. The membrane technology team of Lanzhou Institute has gradually developed into today’s Gansu Membrane Science and Technology Research Institute.
• In December 1974, in order to solve the serious water shortage in Tianjin and other places, the National Leading Group of Science and Technology in Beijing organized a national desalination science and technology work conference, and developed a “1975-1985 national desalination science and technology development plan”. Two Bureau of Oceanography, Lanzhou glacial permafrost desert, Beijing Environmental Chemistry, Tianjin Institute of Synthetic Materials, Chinese Academy of Sciences Institute of Oceanography and other units involved in reverse osmosis technology research.
• In the mid-to-late 1970s, some domestic units followed the international technology trends, hollow fiber and roll reverse osmosis element research, and the 80s to achieve the initial industrialization. 80s to restart the development of composite membranes, after the seventh five, eight five research and pilot scale up success, China’s reverse osmosis membrane technology began to move from laboratory research to industrial-scale applications.
• China began to apply reverse osmosis technology in the late 1980s, since then the rapid increase in the scale of application. 1988, China’s market sales of 8-inch membranes for 600. 1990, Daya Bay Nuclear Power Station built the first set of reverse osmosis seawater desalination plant, daily production of 200 tons of fresh water. 1999, Dalian City built the first set of 1000 tons / day of reverse osmosis seawater desalination plant. 2005 In 2009, Qingdao built its first reverse osmosis seawater desalination plant with a capacity of 10,000 tons/day, and Tianjin built its first reverse osmosis seawater desalination plant with a capacity of 100,000 tons/day.
• By the end of 2018, China had built a total of 121 reverse osmosis seawater desalination projects, with a desalination scale of 825,641 tons/day. In 2014, 1.8 million reverse osmosis membranes were used in Chinese factories, producing 27 million tons of water per day.
• In the last 20 years, China’s reverse osmosis membrane domestic capacity has also been improving. 2000, China’s first domestic reverse osmosis membrane manufacturer – Huitong Yuanquan was established in the Southern Huitong Science and Technology Park, 2002, Huitong Yuanquan began mass production and sales of polyamide composite reverse osmosis membrane elements. 2006, Huitong Yuanquan name change In 2010, the name was changed again to TimesWharton Technology Co.
• In addition to TimesWharton and Blue Star Toray, many domestic reverse osmosis membrane manufacturers such as Hunan Qinsen and Shandong Juzhang Membrane also appeared one after another.

Summary And Outlook

• The invention and large-scale application of reverse osmosis technology is a remarkable scientific achievement in the history of mankind. The original impetus for this invention came from mankind’s dream of asking the ocean for water. The nearly 70-year history of reverse osmosis technology perfectly tells the story of how mankind has used science and technology to turn this dream into reality.
• Looking back at this history, it should be said that the U.S. government’s special funding program for the early development of reverse osmosis technology has played a great role in promoting, to a large extent, established the U.S. leading position in reverse osmosis technology. From the innovation chain, Hassler, Reed and other pioneers put forward the right idea, established the correct direction of research in reverse osmosis technology; Lobe and Solirajin’s pioneering work to fill the largest technical gap between the concept of reverse osmosis from concept to practice; Cadotte, Bray, Spatz and others with scientist quality and entrepreneurial spirit, in promoting reverse osmosis from technology to product leap.
• From an R&D standpoint, the work of Loeb and Soliragin in synthesizing the first asymmetric reverse osmosis membrane was remarkable but not miraculous. Lobe reviewed the experience in detail in 1980. They started with proof of concept and identification of gaps, moved on to analyzing the causes and developing hypotheses, improved the solution, verified the hypotheses, and finally succeeded. It was a combination of luck and inspiration, inspired by the literature, and helpful advice from colleagues, just like the stories around us.
• In recent years, the application of reverse osmosis technology has increasingly expanded into the field of industrial water treatment, especially industrial wastewater reuse and zero discharge treatment. On the one hand, this has put forward higher requirements for reverse osmosis membranes in terms of pollution resistance and cleaning resistance, and on the other hand, it has also placed higher expectations on the concentration capacity of reverse osmosis. New reverse osmosis membrane products and processes such as dish and tube reverse osmosis (DTRO), high pressure reverse osmosis (HPRO), high salt reverse osmosis (HSRO), etc. have emerged.
• Looking to the future, reverse osmosis technology will continue to expand the application areas and scale, and may even overturn the technical framework established 40 years ago. With the accumulation of technology, talent and experience, the technical barriers between domestic reverse osmosis membrane and imported brands are disappearing, and it is only a matter of time before the domestic membrane fully replaces the imported membrane. In addition, as China is the world’s leading industrial wastewater reuse and zero discharge market, which provides favorable conditions for domestic reverse osmosis membrane technology in the future to achieve technology beyond.

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