Reverse osmosis or RO system is a popular water treatment process in which feed water passes through the small pores semi permeable membrane to separate dissolved solutes. It is widely used to produce pure water for drinking purposes. It is possible to remove various salts and other effluent materials from water molecules by applying this process.
A semi-permeable membrane is used to pass water into it after applying pressure. The impure water flows through this membrane from the more concentrated side to the less concentrated side to produce pure water. The wastewater or brine is left over the membrane, whereas the freshwater flows through the pipe to drink.
This treatment mechanism was first introduced in the year 1950 to remove the various salts from seawater. This process was not fully developed at that time. After a lot of research to develop this process, it was possible to develop significantly after some years in the field of polymers and the production of efficient membranes.
This crucial technique is used to purify water for industrial, residential, commercial, and scientific purposes. This process has the ability to remove 90% to 99% of all contaminants from impure water. It helps to reject all particles, bacteria, and organics > 200 Dalton molecular weight.
Reverse Osmosis Definition
Reverse osmosis or RO) is an advanced process to remove all particles, ions, and molecules from a solution by passing through it a semi-permeable membrane that has very small holes or “pores.” The membrane of this system contains a thin layer of polymeric material capable of removing the particles, ions, and molecules by applying pressure. The impurities are left behind and flushed away after completing the process and provide clean water to drink.
A definite amount of pressure is applied to overcome osmotic pressure for removing ions, unwanted molecules, and larger particles from drinking water in this process. It is possible to reject the various dissolved and suspended chemical species as well as biological ones from water by applying this crucial technique. The smaller components of the solution like water molecules move easily through this membrane, whereas large molecules or ions cannot pass through the pores (holes) of the semi-permeable membrane.
Reverse Osmosis History
The osmosis process was first introduced by Jean-Antoine Nollet in 1748. He was able to prove that a selected solvent can be passed through a membrane by applying the process of natural osmotic pressure. Over the next 200 years, the osmosis process was developed slowly. The researchers of the University of California at Los Angeles used to osmosis and semipermeable membranes as a solution to remove the salt from seawater in 1949. Then researchers from both the University of California and the University of Florida were able to produce pure water from seawater in 1950.
Then a lot of research was done to develop this process. Then the semi-permeable membrane was produced by interfacial polymerization of m-phenylenediamine and trimethyl chloride to run this process easily in different areas. This advanced treatment process is used widely for its reliable water treatment process. This process became more popular at the beginning 21st century for desalinating and removing all unnecessary particles from water.
Reverse Osmosis Principle
This advanced treatment process consists of a semi-permeable membrane. At first, a force of pressure is generally applied on the semi-permeable membrane to create a concentration gradient. Then the water molecules can move through the membrane and leave behind all dissolved solids. The particles, ions, and unnecessary molecules are unable to cross through it and they remain on the pressurized side. The pure solvent-like water molecules pass through it easily from the high-concentration to the low-concentration side.
The semi-permeable membrane does not allow crossing the ions like Na+, Ca2+, Mg2+ or larger molecules like glucose, fructose, urea, bacteria, etc. It must apply a sufficient amount of pressure from the ‘concentrated’ side of the membrane to run this activity.
This process differs from general filtration methods as the fluid flow is possible easily by osmosis across a membrane. Size exclusion or straining methods are applied in the membrane filtration method where the hole diameters are approximately 0.01 micrometers or larger in size. However the reverse osmosis (RO) process relates to the solvent diffusion based on the pressure, solute concentration, and many other conditions. The membrane holes of the RO process are 0.001 micrometers in size.
Reverse Osmosis Process/Steps
Pre-treatment
The feed water or tap water should be pretreated to extend the life of the membrane because most of the time it is seen that feed water contains manganese, sodium, hydrogen sulfide or iron. It is also important to remember the adjusting of pH level to control scaling.
The main stages of the reverse osmosis process are discussed below:
Step 1: The feed water or tap water is passed through a particle filter media to reject the silt, sediment, sand, and clay particles that might clog the R/O membrane.
Step 2: The water molecules are then passed through an activated carbon filter to remove the minerals and contaminants such as chromium, arsenic, mercury, copper, chloramines, pesticides, etc from the water molecules and increase the lifetime of the membrane.
Step 3: Water is then transferred into the R/O module. The particles, ions, and various remaining wastes cannot able to cross the membrane and be flushed down the drain, whereas clean water is passed through the small pores in the semi-permeable membrane.
Step 4: The pure treated water is then passed through a pipeline to be stored in a tank.
Post-treatment
The treated water can be further treated to increase the purity to use for various purposes where needs ultra-pure water. UV lamp is used nowadays with this process to destroy 99.99% of harmful pathogens by attacking their genetic core, thereby eliminating their ability to reproduce. Finally, an ultrafiltration (UF) method is applied where the water is forced to pass through a type of hollow fiber membrane to deliver pure and clean water.
Reverse Osmosis (RO) System Benefits/Advantages
This process is essential to remove a wide range of contaminants from water. It helps to reject a lot of impurities like chlorine, lead, arsenic, nitrates, fluoride, and more to provide clean water. The water produced from this process is healthy, especially for individuals with compromised immune systems or various health benefits. It increases the refreshing rate as well as the odor and overall quality of the water. This RO system is very helpful to prevent waterborne diseases. This plant can be maintained easily and saves money for water purification.
Reverse Osmosis Disadvantages/Demerits
The cellulose acetate membrane which can be used as the semi-permeable membrane has limited pH tolerance. This polymeric membrane can be hydrolyzed and vulnerable to bacteria. It can be degraded when the temperature is more than 350C. Polyamide polymeric membrane is also degraded when the temperature crosses 350C. This membrane can lose its activity due to the presence of free chlorine in wastewater.
Reverse Osmosis Applications/Uses
This process is very popular for water filtration purposes in commercial and residential fields. It is a very effective method to desalinate the seawater. The harmful particles, metals, organic contaminants, and pathogens can be rejected from feed water through this treatment method. This process is very suitable for purifying ethanol or grain alcohol to increase its proof. A lot of waterborne diseases can be removed by applying this RO system.
This process is a reliable system for water purification and water filtration system. It is also used in various types of food industries for the concentration of juices, milk, and other beverages.
Difference between Osmosis and Reverse Osmosis
The osmosis process relates the diffusion of water molecules through a semi-permeable membrane from a high water potential area to a lower one while the reverse osmosis process relates the passing of water molecules through a semi-permeable membrane against the concentration gradient.
The osmosis system requires less energy than the reverse osmosis (RO) system.
The osmosis process is a naturally occurring system while the RO system is used commercially for different purposes.
Frequently Asked Questions (FAQs)
What is reverse osmosis (RO) process?
It is an important water filtration system to remove various types of wastes from water by applying pressure and passing the feed water through the semi-permeable polymer matrix molecules.
How does reverse osmosis work?
This process works by applying a sufficient amount of pressure with a pump on the salt side of the RO and forcing the water across the semi-permeable membrane to remove all (around 99 %) dissolved salts from the feed water.
What contaminants does Reverse Osmosis (RO) remove?
This process is very efficient in removing the protozoa such as Giardia and Cryptosporidium. An RO system is essential to withdraw the bacteria including Salmonella, Shigella, and coliforms such as E. coli. A lot of viruses including Hepatitis A, Nor virus, and Rotavirus can be rejected by applying this process. The mineral atoms like calcium, magnesium, sodium, etc can be removed easily by this advanced technique.
What are the uses of reverse osmosis filters?
This treatment process is very suitable for water filtration and water purification in different fields by pushing water through a membrane under pressure. High-quality pure water can be produced through this technique that can be used in various fields like the field of medicine.
What is osmosis?
It is a process in which a feed water molecule passes through a polymerized semi-permeable membrane from a diluted solution into a more concentrated solution.
What is the principle of reverse osmosis?
RO process relates to the removal of ions, unwanted molecules, and all particles from feed water by using a semi-permeable membrane. The solute can be kept on the membrane’s pressurized side while the pure water molecule is allowed to pass to the other side.
