Osmosis | Define Osmosis at Dictionary.com osmosis [oz-moh-sis, os-] /ɒzˈmoʊ sɪs, ɒs-/ Spell 1. Physical Chemistry, Cell Biology. the tendency of a fluid, usually water, to pass through a semipermeable membrane into a solution where the solvent concentration is higher, thus equalizing the concentrations of materials on either side of the membrane. the diffusion of fluids through membranes or porous partitions. a subtle or gradual absorption or mingling: He never studies but seems to learn by osmosis.

Origin of osmosis Expand 1865-1870 1865-70; Latinized form of now obsolete osmose osmosis, extracted from endosmose endosmosis, exosmose exosmosis < French, equivalent to end- end- , ex- ex- 2 + Greek ōsm(ós) push, thrust + French -ose -osis Related forms [oz-mot-ik, os-] /ɒzˈmɒt ɪk, ɒs-/ (Show IPA), adjective osmotically, adverb Examples from the Web for osmosis Expand Historical Examples This fat absorption thus appears to be a vital process, and not one simply controlled by physical forces like osmosis. A Civic Biology George William Hunter "I believe that story of the duck that understood the theory of osmosis," said Mr. Burroughs. A Civic Biology George William Hunter Nourishment passes through them by a simple process of osmosis. Embryology Gerald R. Leighton Ontario Teachers' Manuals: Nature Study Ontario Ministry of Education osmosis takes place when two fluids of different osmotic pressure are separated by animal membrane.

British Dictionary definitions for osmosis Expand noun 1. the passage of a solvent through a semipermeable membrane from a less concentrated to a more concentrated solution until both solutions are of the same concentration 2. diffusion through any membrane or porous barrier, as in dialysis 3. gradual or unconscious assimilation or adoption, as of ideas Derived Forms C19: Latinized form from osmose (n), from Greek ōsmos push, thrust Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for osmosis Expand n.

1867, Latinized from osmose (1854), shortened from endosmosis (1830s), from endosmose "inward passage of a fluid through a porous septum" (1829), from French endo- "inward" + Greek osmos "a thrusting, a pushing," from stem of othein "to push, to thrust," from PIE *wedhe- "to push, strike" (cf. Sanskrit vadhati "pushes, strikes, destroys," Avestan vadaya- "to repulse"). Figurative sense is from 1900. Related: Osmotic (1854, from earlier endosmotic). Online Etymology Dictionary, © 2010 Douglas Harper osmosis (ŏz-mō'sĭs) The movement of a solvent through a membrane separating two solutions of different concentrations. The solvent from the side of weaker concentration usually moves to the side of the stronger concentration, diluting it, until the concentrations of the solutions are equal on both sides of the membrane.

◇ The pressure exerted by the molecules of the solvent on the membrane they pass through is called osmotic pressure. Osmotic pressure is the energy driving osmosis and is important for living organisms because it allows water and nutrients dissolved in water to pass through cell membranes. The American Heritage® Science Dictionary Copyright © 2002. Published by Houghton Mifflin. All rights reserved. What is Osmosis? What is Osmosis? 10 Answers 0 Osmosis is the net movement of a solvent across a semipermeable membrane from a region of high solvent potential to an area of low solvent potential down a concentration gradient. It is a physical process in which a solvent moves, without input of energy, across a semipermeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations.[1] Osmosis releases energy, and can be made to do work, as when a growing tree-root splits a stone.

Computer simulation of the process of osmosis Computer simulation of the process of osmosis Net movement of solvent is from the less-concentrated (hypotonic), to the more-concentrated (hypertonic) solution, which tends to reduce the difference in concentrations. This effect can be countered by increasing the pressure of the hypertonic solution, with respect to the hypotonic. The osmotic pressure is defined to be the pressure required to maintain an equilibrium, with no net movement of solvent. Osmotic ... more answers.yahoo.com Is this page helpful to you? Your anonymous feedback will help us improve. Related Videos 0 Osmosis refers to the passage of water across a thin membrane from a dilute solution to a more concentrated one. In other words, water moves through the semi-permeable barrier trying to even out the difference in concentration between the two sides. 2) What is reverse osmosis (RO)? The other side of the coin is reverse osmosis. A pump is used to cause a difference in pressure. This difference in pressure means that that water is forced through the membrane. Pure water molecules (H2O) are small enough to pass through the membrane whilst larger solute molecules get trapped.

When water is processed by reverse osmosis a large fraction of dissolved material is removed. The cleaner the input water the cleaner the output water will be. Conversely, if your input water is clean enough, you may not need an RO unit. 3) How does RO equipment work? There are 3 stages to R.O. filtration: 1. A pre-filter (PR1-25-OE) initially removes larger suspended particles from the raw water 2. Water is forced ... freshwaterfilter.com Write a comment... 0 Osmosis quite simply is the physical process by which a liquid from a weaker medium is drawn through a semi-permeable membrane into a stronger liquid medium. So what does this mean and how does this relate to boat hull damage? The simple answer is probably not a lot! Contradicting earlier theories, the damage from “osmosis” is not caused by excessive water permeation. There are absolutely no osmotic forces involved as the gelcoat is an absorbing material which can never act as an osmotic membrane! Instead it is the process of hydrolysis, which creates the water soluble corrosive products which in turn create the familiar cavities.

(Hydrolysis is the general term given to the reaction of any material with water, for example organic compounds like polyester resin, itself the main constituent of GRP laminates.) Once the cavities have formed, then excess water will enter giving rise to high moisture readings. This process may normally be slow, but the presence of free acids or alkalis ... more hotvac.com Write a comment... 0 This is called osmosis, the reason it is important is that all living cells are covered with these materials which will let water through but not salt or sugars ( they are called partially permiable membranes by the way) so if you stay in a bath too long water moves into your skin and your fingers go all wrinkley, if you go swimming in the sea and get covered with salt, you get really thirsty as the water is sucked out of you by the salt and osmosis, and for the same reason snails shrivel up when you pour salt on them.... oh and it drives lots of important biological processes. more chaosscience.org.uk Write a comment... 0 It is the phenomenon of water flow through a semi-permeable membrane that blocks the transport of salts or other solutes through it. Osmosis is a fundamental effect in all biological systems.

It is applied to water purification and desalination, waste material treatment, and many other chemical and biochemical laboratory and industrial processes. When two water (or other solvent) volumes are separated by a semi-permeable membrane, water will flow from the volume of low solute concentration, to the volume of high solute concentration. The flow may be stopped, or even reversed by applying external pressure on the volume of higher concentration. In such a case the phenomenon is called reverse osmosis. If there are solute molecules only in one volume of the system, then the pressure on it, that stops the flow, is called the osmotic pressure. The thermal movement of a solute molecule within a solvent is over damped by the solvent molecules that surround it. The solute movement is wholly ... more members.tripod.com Write a comment... 0 Unfortunately osmosis is where the concept of diffusion gets even more confusing. Rather than the simple process of one chemical evening itself out, osmosis relates to a situation where something is dissolved in something else. It is initially rather important that you understand the difference between a solvent and a solute - a solute being the thing which is dissolved, and the solvent being the thing which it is dissolved in.

If you make a cup of tea and decide to have some sugar in it, then the drink of tea is the solvent because you are dissolving into the tea, and the sugar is the solute, because it is dissolving into it. The definition of osmosis is very difficult to understand, but once it is explained, it makes a lot more sense. Put very simply, osmosis - when refering to water - is effectively the diffusion of water molecules. The strict definition is the diffusion of a solvent, through a partially permeable membrane, from an area of low concentration to an area of high ... more blobs.org Write a comment... 0 Osmosis is a process in which a fluid passes through a semipermeable membrane, moving from an area in which a solute such as salt is present in low concentrations to an area in which the solute is present in high concentrations.

The end result of osmosis, barring external factors, will be equal amounts of fluid on either side of the barrier, creating a state which is known as “isotonic.” The fluid most commonly used in demonstrations of osmosis is water, and osmosis with a wide variety of fluid solutions is key for every living organism on Earth, from humans to plants. There are some key terms related to osmosis which may be helpful to know when thinking about how osmosis works. The fluid which passes through the membrane is known as a solvent, while the dissolved substance in the fluid is a solute. Together, the solvent and dissolved solute make up a solution. When a solution has low levels of a solute, it is considered to be hypotonic, while solutions with high solute levels are ... more wisegeek.com Write a comment... 0 Osmosis is based upon the fundamental pursuit for balance. Two fluids containing different concentrations of dissolved solids that come in contact with each other will mix until the concentration is uniform.

When these two fluids are separated by a semi permeable membrane (which lets the fluid flow through, while dissolved solids stay behind), the fluid containing the lower concentration will move through the membrane into the fluid containing the higher concentration of dissolved solids (Binnie e.a., 2002). After a while the water level will be higher on one side of the membrane. The difference in height is called the osmotic pressure. What is Reverse Osmosis? By applying a pressure that exceeds the osmotic pressure, the reverse effect occurs. Fluids are pressed back through the membrane, while dissolved solids stay behind. To purify water by Reverse Osmosis membrane, the natural osmosis effect must be reversed. In order to force the water of the brine stream (high salt ... more lenntech.com Write a comment... 0 How Osmosis Affects GRP Hulls Osmosis is the condition of visible blisters on a boat's hull, caused by water absorption. The process of osmosis is the same mechanism by which plants and trees draw water up from the soil to their branches and leaves. Main Causes of Osmosis. Long periods afloat without lay-ups. Warm tropical waters.

Fresh water is worse than salt water. Resins that are coloured (including white ones) are more affected than clear resins. The Process of Osmosis. The fibreglass mouldings on a yacht hull are not completely waterproof. Individual water molecules are so small that they can find their way into the layers of glass and resin which form the boat's hull. Problems start to occur when water molecules merge with other chemicals inside the laminate. These are chemicals such as water-soluble materials, emulsion binders for example. The water molecules can then have a chemical reaction with these substances, forming larger molecules of a new chemical, often acidic. ... articleblotter.com Ultrapure… | Puretec Industrial Water :: Ultrapure Water Solutions Summary Understanding Reverse Osmosis Reverse Osmosis, commonly referred to as RO, is a process where you demineralize or deionize water by pushing it under pressure through a semi-permeable Reverse Osmosis Membrane. Osmosis To understand the purpose and process of Reverse Osmosis you must first understand the naturally occurring process of Osmosis. Osmosis is a naturally occurring phenomenon and one of the most important processes in nature.

It is a process where a weaker saline solution will tend to migrate to a strong saline solution. Examples of osmosis are when plant roots absorb water from the soil and our kidneys absorb water from our blood. Below is a diagram which shows how osmosis works. A solution that is less concentrated will have a natural tendency to migrate to a solution with a higher concentration. For example, if you had a container full of water with a low salt concentration and another container full of water with a high salt concentration and they were separated by a semi-permeable membrane, then the water with the lower salt concentration would begin to migrate towards the water container with the higher salt concentration. A semi-permeable membrane is a membrane that will allow some atoms or molecules to pass but not others. A simple example is a screen door. It allows air molecules to pass through but not pests or anything larger than the holes in the screen door. Another example is Gore-tex clothing fabric that contains an extremely thin plastic film into which billions of small pores have been cut. The pores are big enough to let water vapor through, but small enough to prevent liquid water from passing. Reverse Osmosis is the process of Osmosis in reverse.

Whereas Osmosis occurs naturally without energy required, to reverse the process of osmosis you need to apply energy to the more saline solution. A reverse osmosis membrane is a semi-permeable membrane that allows the passage of water molecules but not the majority of dissolved salts, organics, bacteria and pyrogens. However, you need to 'push' the water through the reverse osmosis membrane by applying pressure that is greater than the naturally occurring osmotic pressure in order to desalinate (demineralize or deionize) water in the process, allowing pure water through while holding back a majority of contaminants. Below is a diagram outlining the process of Reverse Osmosis. When pressure is applied to the concentrated solution, the water molecules are forced through the semi-permeable membrane and the contaminants are not allowed through. How does Reverse Osmosis work? Reverse Osmosis works by using a high pressure pump to increase the pressure on the salt side of the RO and force the water across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts behind in the reject stream. The amount of pressure required depends on the salt concentration of the feed water.

The more concentrated the feed water, the more pressure is required to overcome the osmotic pressure. The desalinated water that is demineralized or deionized, is called permeate (or product) water. The water stream that carries the concentrated contaminants that did not pass through the RO membrane is called the reject (or concentrate) stream. As the feed water enters the RO membrane under pressure (enough pressure to overcome osmotic pressure) the water molecules pass through the semi-permeable membrane and the salts and other contaminants are not allowed to pass and are discharged through the reject stream (also known as the concentrate or brine stream), which goes to drain or can be fed back into the feed water supply in some circumstances to be recycled through the RO system to save water. The water that makes it through the RO membrane is called permeate or product water and usually has around 95% to 99% of the dissolved salts removed from it. It is important to understand that an RO system employs cross filtration rather than standard filtration where the contaminants are collected within the filter media.

With cross filtration, the solution passes through the filter, or crosses the filter, with two outlets: the filtered water goes one way and the contaminated water goes another way. To avoid build up of contaminants, cross flow filtration allows water to sweep away contaminant build up and also allow enough turbulence to keep the membrane surface clean. What contaminants will Reverse Osmosis remove from water? Reverse Osmosis is capable of removing up to 99%+ of the dissolved salts (ions), particles, colloids, organics, bacteria and pyrogens from the feed water (although an RO system should not be relied upon to remove 100% of bacteria and viruses). An RO membrane rejects contaminants based on their size and charge. Any contaminant that has a molecular weight greater than 200 is likely rejected by a properly running RO system (for comparison a water molecule has a MW of 18). Likewise, the greater the ionic charge of the contaminant, the more likely it will be unable to pass through the RO membrane. For example, a sodium ion has only one charge (monovalent) and is not rejected by the RO membrane as well as calcium for example, which has two charges.

Likewise, this is why an RO system does not remove gases such as CO2 very well because they are not highly ionized (charged) while in solution and have a very low molecular weight. Because an RO system does not remove gases, the permeate water can have a slightly lower than normal pH level depending on CO2 levels in the feed water as the CO2 is converted to carbonic acid. Reverse Osmosis is very effective in treating brackish, surface and ground water for both large and small flows applications. Some examples of industries that use RO water include pharmaceutical, boiler feed water, food and beverage, metal finishing and semiconductor manufacturing to name a few. Reverse Osmosis Performance & Design Calculations There are a handful of calculations that are used to judge the performance of an RO system and also for design considerations. An RO system has instrumentation that displays quality, flow, pressure and sometimes other data like temperature or hours of operation. In order to accurately measure the performance of an RO system you need the following operation parameters at a minimum: Feed pressure Temperature Salt Rejection % This equation tells you how effective the RO membranes are removing contaminants. It does not tell you how each individual membrane is performing, but rather how the system overall on average is performing.

A well-designed RO system with properly functioning RO membranes will reject 95% to 99% of most feed water contaminants (that are of a certain size and charge). You can determine how effective the RO membranes are removing contaminants by using the following equation: Salt Rejection % = Conductivity of Feed Water – Conductivity of Permeate Water × 100 Conductivity of Feed The higher the salt rejection, the better the system is performing. A low salt rejection can mean that the membranes require cleaning or replacement. Salt Passage % This is simply the inverse of salt rejection described in the previous equation. This is the amount of salts expressed as a percentage that are passing through the RO system. The lower the salt passage, the better the system is performing. A high salt passage can mean that the membranes require cleaning or replacement. Salt Passage % = (1 – Salt Rejection %) Recovery % Percent Recovery is the amount of water that is being 'recovered' as good permeate water. Another way to think of Percent Recovery is the amount of water that is not sent to drain as concentrate, but rather collected as permeate or product water.

The higher the recovery % means that you are sending less water to drain as concentrate and saving more permeate water. However, if the recovery % is too high for the RO design then it can lead to larger problems due to scaling and fouling. The % Recovery for an RO system is established with the help of design software taking into consideration numerous factors such as feed water chemistry and RO pre-treatment before the RO system. Therefore, the proper % Recovery at which an RO should operate at depends on what it was designed for. By calculating the % Recovery you can quickly determine if the system is operating outside of the intended design. The calculation for % Recovery is below: % Recovery = × 100 Feed Flow Rate (gpm) For example, if the recovery rate is 75% then this means that for every 100 gallons of feed water that enter the RO system, you are recovering 75 gallons as usable permeate water and 25 gallons are going to drain as concentrate. Industrial RO systems typically run anywhere from 50% to 85% recovery depending the feed water characteristics and other design considerations. Concentration Factor The concentration factor is related to the RO system recovery and is an important equation for RO system design.

The more water you recover as permeate (the higher the % recovery), the more concentrated salts and contaminants you collect in the concentrate stream. This can lead to higher potential for scaling on the surface of the RO membrane when the concentration factor is too high for the system design and feed water composition. Concentration Factor = 1 1 – Recovery % The concept is no different than that of a boiler or cooling tower. They both have purified water exiting the system (steam) and end up leaving a concentrated solution behind. As the degree of concentration increases, the solubility limits may be exceeded and precipitate on the surface of the equipment as scale. For example, if your feed flow is 100 gpm and your permeate flow is 75 gpm, then the recovery is (75/100) x 100 = 75%. To find the concentration factor, the formula would be 1 ÷ (1-75%) = 4. A concentration factor of 4 means that the water going to the concentrate stream will be 4 times more concentrated than the feed water is.

If the feed water in this example was 500 ppm, then the concentrate stream would be 500 x 4 = 2,000 ppm. Flux gpm of permeate × 1,440 min/day # of RO elements in system × square footage of each RO element For example, you have the following: The RO system is producing 75 gallons per minute (gpm) of permeate. You have 3 RO vessels and each vessel holds 6 RO membranes. Therefore you have a total of 3 x 6 = 18 membranes. The type of membrane you have in the RO system is a Dow Filmtec BW30-365. This type of RO membrane (or element) has 365 square feet of surface area. To find the flux (Gfd): Gfd = 18 elements × 365 sq ft 6,570 The flux is 16 Gfd. This means that 16 gallons of water is passed through each square foot of each RO membrane per day. This number could be good or bad depending on the type of feed water chemistry and system design.

Below is a general rule of thumb for flux ranges for different source waters and can be better determined with the help of RO design software. If you had used Dow Filmtec LE-440i RO membranes in the above example, then the flux would have been 14. So it is important to factor in what type of membrane is used and to try and keep the type of membrane consistent throughout the system. Feed Water Source ((3,500 - 2,450) / (3,500 + 2,450)) * 100 = 18% A difference of +/- 5% is ok. A difference of +/- 5% to 10% is generally adequate. A difference of > +/- 10% is unacceptable and calibration of the RO instrumentation is required to ensure that you are collecting useful data. In the example above, the RO mass balance equation falls out of range and requires attention. Understanding the difference between passes and stages in a Reverse Osmosis (RO) system The terms stage and pass are often mistaken for the same thing in an RO system and can be confusing terminology for an RO operator.

It is important to understand the differnce between a 1 and 2 stage RO and a 1 and 2 pass RO. Difference between a 1 and 2 stage RO System In a one stage RO system, the feed water enters the RO system as one stream and exits the RO as either concentrate or permeate water. In a two-stage system the concentrate (or reject) from the first stage then becomes the feed water to the second stage. The permeate water is collected from the first stage is combined with permeate water from the second stage. Additional stages increase the recovery from the system. Array In a Reverse Osmosis System an array describes the physical arrangement of the pressure vessels in a 2 stage system. Pressure vessels contain RO membranes (usually from 1 to 6 RO membranes are in a pressure vessel). Each stage can have a certain amount of pressure vessels with RO membranes. The reject of each stage then becomes the feed stream for the next successive stage. The 2 stage RO system displayed on the previous page is a 2:1 array which means that the concentrate (or reject) of the first 2 RO vessels is fed to the next 1 vessel.

RO System with Concentrate Recycle With an RO system that can't be properly staged and the feed water chemistry allows for it, a concentrate recycle setup can be utilized where a portion of the concentrate stream is fed back to the feed water to the first stage to help increase the system recovery. Single Pass RO vs Double Pass RO Think of a pass as a stand alone RO system. With this in mind, the difference between a single pass RO system and a double pass RO system is that with a double pass RO, the permeate from the first pass becomes the feed water to the second pass (or second RO) which ends up producing a much higher quality permeate because it has essentially gone through two RO systems. Besides producing a much higher quality permeate, a double pass system also allows the opportunity to remove carbon dioxide gas from the permeate by injecting caustic between the first and second pass. C02 is undesirable when you have mixed bed ion exchange resin beds after the RO. By adding caustic after the first pass, you increase the pH of the first pass permeate water and convert C02 to bicarbonate (HCO3-) and carbonate (CO3-2) for better rejection by the RO membranes in the second pass.

This can't be done with a single pass RO because injecting caustic and forming carbonate (CO3-2) in the presence of cations such as calcium will cause scaling of the RO membranes. RO Pretreatment Proper pretreatment using both mechanical and chemical treatments is critical for an RO system to prevent fouling, scaling and costly premature RO membrane failure and frequent cleaning requirements. Below is a summary of common problems an RO system experiences due to lack of proper pretreatment. Fouling Fouling occurs when contaminants accumulate on the membrane surface effectively plugging the membrane. There are many contaminants in municipal feed water that are naked to the human eye and harmless for human consumption, but large enough to quickly foul (or plug) an RO system. Fouling typically occurs in the front end of an RO system and results in a higher pressure drop across the RO system and a lower permeate flow. This translates into higher operating costs and eventually the need to clean or replace the RO membranes. Fouling will take place eventually to some extent given the extremely fine pore size of an RO membrane no matter how effective your pretreatment and cleaning schedule is. However, by having proper pretreatment in place, you will minimize the need to address fouling related problems on a regular basis.

Fouling can be caused by the following: Particulate or colloidal mater (dirt, silt, clay, etc.) Organics (humic/fulvic acids, etc) Microorganisms (bacteria, etc). Bacteria present one of the most common fouling problems since RO membranes in use today cannot tolerate a disinfectant such as chlorine and thefore microorganisms are often able to thrive and multiply on the membrane surface. They may product biofilms that cover the membrane surface and result in heavy fouling. Breakthrough of filter media upstream of the RO unit. GAC carbon beds and softener beds may develop an under drain leak and if there is not adequate post filtration in place the media can foul the RO system. By performing analytical tests, you can determine if the feed water to your RO has a high potential for fouling. To prevent fouling of an RO system, mechanical filtration methods are used. The most popular methods to prevent fouling are the use of multi-media filters (MMF) or microfiltration (MF). In some cases cartridge filtration will suffice.

Scaling As certain dissolved (inorganic) compounds become more concentrated (remember discussion on concentration factor) then scaling can occur if these compounds exceed their solubility limits and precipitate on the membrane surface as scale. The results of scaling are a higher pressure drop across the system, higher salt passage (less salt rejection), low permeate flow and lower permeate water quality. An example of a common scale that tends to form on an RO membrane is calcium carbonate (CaCO3). Chemical Attack Modern thin film composite membranes are not tolerant to chlorine or chloramines. Oxidizers such as chlorine will 'burn' holes in the membrane pores and can cause irreparable damage. The result of chemical attack on an RO membrane is a higher permeate flow and a higher salt passage (poorer quality permeate water). This is why microorganism growth on RO membranes tends to foul RO membranes so easily since there is no biocide to prevent its growth. Mechanical Damage Part of the pretreatment scheme should be pre and post RO system plumbing and controls. If 'hard starts' occur mechanical damage to the membranes can occur. Likewise, if there is too much backpressure on the RO system then mechanical damage to the RO membranes can also occur.

These can be addressed by using variable frequency drive motors to start high pressure pumps for RO systems and by installing check valve(s) and/or pressure relief valves to prevent excessive back pressure on the RO unit that can cause permanent membrane damage. Pretreatment Solutions Below are some pretreatment solutions for RO systems that can help minimize fouling, scaling and chemical attack. Multi Media Filtration (MMF) A Multi-Media Filter is used to help prevent fouling of an RO system. A Multi-Media Filter typically contains three layers of media consisting of anthracite coal, sand and garnet, with a supporting layer of gravel at the bottom. These are the medias of choice because of the differences in size and density. The larger (but lighter) anthracite coal will be on top and the heavier (but smaller) garnet will remain on the bottom. The filter media arrangement allows the largest dirt particles to be removed near the top of the media bed with the smaller dirt particles being retained deeper and deeper in the media. This allows the entire bed to act as a filter allowing much longer filter run times between backwash and more efficient particulate removal.

A well-operated Multi-Media Filter can remove particulates down to 15-20 microns. A Multi-Media Filter that uses a coagulant addition (which induces tiny particles to join together to form particles large enough to be filtered) can remove particulates down to 5-10 microns. To put this in perspective, the width of a human hair is around 50 microns. A multi media filter is suggested when the Silt Density Index (SDI) value is greater than 3 or when the turbidity is greater than 0.2 NTU. There is no exact rule, but the above guidelines should be followed to prevent premature fouling of RO membranes. It is important to have a 5 micron cartridge filter placed directly after the MMF unit in the event that the under drains of the MMF fail. This will prevent the MMF media from damaging downstream pumps and fouling the RO system. Microfiltration (MF) Microfiltration (MF) is effective in removing colloidal and bacteria matter and has a pore size of only 0.1-10µm. Microfiltration is helpful in reducing the fouling potential for an RO unit.

Membrane configuration can vary between manufacturers, but the "hollow fiber" type is the most commonly used. Typically, the water is pumped from the outside of the fibers, and the clean water is collected from the inside of the fibers. Microfiltration membranes used in potable water applications usually operate in "dead-end" flow. In dead-end flow, all of the water fed to the membrane is filtered through the membrane. A filter cake that must be periodically backwashed from the membrane surface forms. Recovery rates are normally greater than 90 percent on feed water sources which have fairly high quality and low turbidity feeds. Antiscalants and Scale Inhibitors Antiscalants and scale inhibitors, as their name suggests, are chemicals that can be added to feed water before an RO unit to help reduce the scaling potential of the feed water. Antiscalants and scale inhibitors increase the solubility limits of troublesome inorganic compounds. By increasing the solubility limits, you are able to concentrate the salts further than otherwise would be possible and therefore achieve a higher recovery rate and run at a higher concentration factor. Antiscalants and scale inhibitors work by interfering with scale formation and crystal growth.

The choice of antiscalant or scale inhibitor to use and the correct dosage depends on the feed water chemistry and RO system design. Softening by ion exchange A water softener can be used to help prevent scaling in an RO system by exchanging scale forming ions with non scale forming ions. As with a MMF unit, it is important to have a 5 micron cartridge filter placed directly after the water softener in the event that the under drains of the softener fail. Sodium Bisulfite (SBS) injection By adding sodium bisulfite (SBS or SMBS), which is a reducer, to the water stream before an RO at the proper dose you can remove residual chlorine. Granular Activated Carbon (GAC) GAC is used for both removing organic constituents and residual disinfectants (such as chlorine and chloramines) from water. GAC media is made from coal, nutshells or wood. Activated carbon removes residual chlorine and chloramines by a chemical reaction that involves a transfer of electrons from the surface of the GAC to the residual chlorine or chloramines. The chlorine or chloramines ends up as a chloride ion that is no longer an oxidizer.

The disadvantage of using a GAC before the RO unit is that the GAC will remove chlorine quickly at the very top of the GAC bed. This will leave the remainder of the GAC bed without any biocide to kill microorganisms. A GAC bed will absorb organics throughout the bed, which is potential food for bacteria, so eventually a GAC bed can become a breeding ground for bacteria growth which can pass easily to the RO membranes. Likewise, a GAC bed can produce very small carbon fines under some circumstances that have the potential to foul an RO. RO Data Trending and Normalization The RO membranes are the heart of the RO system and certain data points need to be collected to determine the health of the RO membranes. These data points include the system pressures, flows, quality and temperature. Water temperature is directly proportional to pressure. As the water temperature decreases it becomes more viscous and the RO permeate flow will drop as it requires more pressure to push the water through the membrane. Likewise, when the water temperature increases the RO permeate flow will increase. As a result, performance data for an RO system must be normalized so that flow variations are not interpreted as abnormal when no problem exists.

The normalized flows, pressures and salt rejection should be calculated, graphed and compared to the baseline data (when the RO was commissioned or after the membranes were cleaned or replaced) to help troubleshoot any problems and also determine when to clean or inspect the membranes for damage. Data normalization helps display the true performance of the RO membranes. As a general rule of thumb, when the normalized change is +/- 15% from the baseline data then you need to take action. If you don't follow this rule then RO membrane cleanings may not be very effective at brining the membranes back to near new performance. RO Membrane Cleaning RO membranes will inevitably require periodic cleaning, anywhere from 1 to 4 times a year depending on the feed water quality. As a general rule, if the normalized pressure drop or the normalized salt passage has increased by 15%, then it is time to clean the RO membranes. If the normalized permeate flow has decreased by 15% then it is also time to clean the RO membranes. You can either clean the RO membranes in place or have them removed from the RO system and cleaned off site by a service company that specializes in this service.

It has been proven that offsite membrane cleaning is more effective at providing a better cleaning than onsite cleaning skids. RO membrane cleaning involves low and high pH cleaners to remove contaminants from the membrane. Scaling is addressed with low pH cleaners and organics, colloidal and biofouling are treated with a high pH cleaner. Cleaning RO membranes is not only about using the appropriate chemicals. There are many other factors involved such as flows, water temperature and quality, properly designed and sized cleaning skids and many other factors that an experienced service group must address in order to properly clean RO membranes. Summary Reverse Osmosis is an effective and proven technology to produce water that is suitable for many industrial applications that require demineralized or deionized water. Further post treatment after the RO system such as mixed bed deionization can increase the quality of the RO permeate and make it suitable for the most demanding applications. Proper pretreatment and monitoring of an RO system is crucial to preventing costly repairs and unscheduled maintenance. With the correct system design, maintenance program, and experienced service support, your RO system should provide many years of high purity water.

Contact Us Puretec Industrial Water provides a complete line of water treatment services and parts across California, Arizona, Nevada, and New Mexico. Osmosis - definition of osmosis by The Free Dictionary Osmosis - definition of osmosis by The Free Dictionary Related to osmosis: reverse osmosis , diffusion os·mo·sis n. pl. os·mo·ses (-sēz) 1. a. Diffusion of fluid through a semipermeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal solute concentration on both sides of the membrane. b. The tendency of fluids to diffuse in such a manner. 2. A gradual, often unconscious process of assimilation or absorption: learned French by osmosis while residing in Paris for 15 years. [From obsolete osmose, from earlier endosmose, from French : Greek endo-, endo- + Greek ōsmos, thrust, push (from ōthein, to push).] os·mot′ic (-mŏt′ĭk) adj. os·mot′i·cal·ly adv.

osmosis (ɒzˈməʊsɪs; ɒs-) n 1. (Biology) the passage of a solvent through a semipermeable membrane from a less concentrated to a more concentrated solution until both solutions are of the same concentration 2. (Chemistry) the passage of a solvent through a semipermeable membrane from a less concentrated to a more concentrated solution until both solutions are of the same concentration 3. (General Physics) diffusion through any membrane or porous barrier, as in dialysis 4. gradual or unconscious assimilation or adoption, as of ideas [C19: Latinized form from osmose (n), from Greek ōsmos push, thrust] osmotic adj n. 1. a. the tendency of a fluid, usu. water, to pass through a semipermeable membrane into a solution where the solvent concentration is higher, thus equalizing the concentrations of materials on either side of the membrane. b. the diffusion of fluids through membranes or porous partitions. 2. a subtle or gradual absorption: to learn by osmosis.

[1865–70; Latinized form of now obsolete osmose osmosis, extracted from endosmose endosmosis < French, =end- end - + Greek ōsm(ós) push, thrust + French -ose -osis ] os•mot′ic (-ˈmɒt ɪk) adj. os•mot′i•cal•ly, adv. osmosis left: The concentration of sugar molecules is greater on the right side of the membrane than on the left. The water molecules are small enough to move across the membrane, but the larger sugar molecules cannot pass through. right: The water molecules move across the membrane until the water and sugar molecules are of equal concentration on both sides. This lowers the water level on the left side and raises it on the right side. os·mo·sis (ŏz-mō′sĭs) The movement of a solvent through a membrane separating two solutions of different concentrations. The solvent from the side of weaker concentration usually moves to the side of the stronger concentration, diluting it, until the concentrations of the solutions are equal on both sides of the membrane.

♦ The pressure exerted by the molecules of the solvent on the membrane they pass through is called osmotic pressure. Osmotic pressure is the energy driving osmosis and is important for living organisms because it allows water and nutrients dissolved in water to pass through cell membranes. osmosis the process by which fluids pass through a semipermeable membrane into a solution of lower concentration to equalize the concentration on both sides of the membrane. — osmotic, adj. See also: Processes the process by which fluids pass through a semipermeable membrane into a solution of lower concentration to equalize the concentration on both sides of the membrane. — osmotic, adj. osmosis 1. Movement of water through a selectively permeable membrane, e.g. a cell membrane. 2. The movement of solvent molecules through a semipermeable membrane from a dilute solution to a more concentrated solution. 3. Diffusion of a fluid (e.g., water) through a semipermeable membrane. ThesaurusAntonymsRelated WordsSynonymsLegend: What is Reverse Osmosis and How Does It Work?

– Water Softener Guide By Ryan Walker / January 15, 2016 What is Reverse Osmosis and How Does It Work? 4.8 (96%) 5 votes Reverse Osmosis, popularly known as RO, is nothing but a technology that is employed in the case of water to get rid of a large number of contaminants from it. This is done by pushing the water under pressure through a membrane that is semi-permeable. In the process of reverse osmosis, water is demineralised or deionised by pushing it through a semi-permeable Reverse Osmosis Membrane. Osmosis Osmosis is a process that naturally occurs, in which a weaker saline solution migrates to a stronger saline solution. This is one of the most important processes occurring in nature. It is through this process that the plant roots absorb water from the soil, and the kidneys absorb water from the blood. It is a general tendency of a lower concentrated solution to migrate to a solution with a higher concentration.

For example, if you take a container full of water with a low amount of salt, and another with a higher concentration of salt, and separate them by a semi-permeable membrane, then the water with the lower salt concentration will start to migrate towards the other. A semi-permeable membrane is a membrane that selectively allows atoms and molecules to pass through it. It only allows some of them to pass. You can take a screen door as an example. It allows only air molecules to pass through it and not pests or dust particles that are larger than the size of the holes in the door. Reverse Osmosis Reverse Osmosis can be called as osmosis in reverse. Osmosis is a natural process and does not require any external pressure to occur. But, in the case of reverse osmosis, more pressure needs to be applied to the saline solution with a higher salt concentration. The membrane used in the process of reverse osmosis is a semi-permeable membrane that allows only water molecules to pass through it and not most of the dissolved organics, salts, bacteria, and pyrogens. A high pressure needs to be applied to push the water through this reverse osmosis membrane.

This needs to be greater than the naturally occurring osmotic pressure. This desalinates, demineralises, or deionises the water to allow pure water to come out. A majority of the contaminants are held back. How does Reverse Osmosis Work? In the process of reverse osmosis, a high pressure pump is used to increase the pressure on the saltier side of the RO and force the water to move across the semi-permeable RO membrane. Around 95% to 99% of the dissolved salts are left behind in the reject stream in this process. The salt concentration of the feed water decides the amount of pressure required for the process. The more the amount of salt in the water is, the more will be the pressure required to be able to overcome the osmotic pressure. The demineralised or deionised, desalinated water that comes out is known as the permeate, or product water. The water stream that is left behind and carries the concentrated contaminants that were unable to pass through the RO membrane is known as the reject, or concentrate stream. Once the feed water enters the RO membrane under the pressure applied, the water molecules are able to pass through the semi-permeable membrane.

The salts and the other contaminants are not allowed to pass, and they are discharged through the reject stream. This is also known as the concentrate or brine stream. It goes in to the drain or can even be fed back in to the feed water supply to be recycled through the RO stream in order to save water. Permeate, or product water, is the water that comes out of the RO stream. It usually has around 95% to 99% of the dissolved removed from it. RO system employs the process of cross filtration other than the standard filtration. In standard filtration, the contaminants are collected within the filter media. In cross filtration, the solution passes through or crosses the filter with two different outlets. The filtered one goes via one outlet, and the contaminated one goes through the other outlet. Cross flow filtration allows the water to sweep away the contaminant build up. This avoids contaminant build-up in the filter. It also allows enough turbulence so that the membrane surface is kept clean.

You might also be interested in reading about: Fleck Water Softener – Reviews and Comparisons of Different Models Contaminants removed by Reverse Osmosis Reverse Osmosis has the capability to remove almost 99% of the dissolved salts or ions, colloids, particles, organics, bacteria, and pyrogens in water. But, it should not be relied upon to remove 100% of the viruses and bacteria. The RO membrane rejects the contaminants on the basis of their size and charge. If a contaminant has a molecular weight greater than 200, it is more likely to get rejected by the RO filter. In the same way, the greater the charge of the contaminant, the more likely it is to be unable to pass through the membrane. For example, sodium ion has a single charge, which means it is monovalent, and it is not rejected by the membrane. Same is the case of calcium. You could use the process of Reverse Osmosis to treat brackish, surface, and ground water for all your applications, be it large or small flows.

Boiler feed water, metal finishing, pharmaceutical, food and beverage, and semiconductor industries are some of the common industries that use the process of RO for filtering water. Reverse Osmosis is known to be a very effective and proven technology for filtering water. The salt produced is suitable for most of the industrial applications that require de-ionised or de-mineralised water. The correct system design, maintenance program, and service support can help your RO system provide many years of efficient supply of high purity water. osmosis nedir, ne demek, osmosis anlamı - Sesli Sözlük teriminin İngilizce İngilizce sözlükte anlamı Picking up knowledge accidentally, without actually seeking that particular knowledge At age fourteen, by a process of osmosis, of dirty jokes, whispered secrets and filthy ballads, Tristram learned of sex.

The net movement of solvent molecules from a region of high solvent potential to a region of lower solvent potential through a partially permeable membrane The movement of water through a semipermeable membrane from an area of low concentration of solute to an area of higher concentration in order to equalize the osmotic pressure created by differences in concentration The movement of water down its concentration gradient A process that maintains equilibrium and involves the diffusion of water from a place of high concentration to a place of low concentration The water travels across a membrane that is differentially permeable The process by which water moves from a weaker to a stronger solution through tiny holes in a semi-permeable membrane In peritoneal dialysis, it is osmosis that causes excess water to pass from the blood into the dialysis fluid the movement of water molecules through a thin membrane The osmosis process occurs in our bodies and is also one method of desalinizing saline water {i} diffusion; permeation; tendency to flow through a membrane and create an equal distribution of material the tendency of a solvent to diffuse through a semipermeable membrane from the less concentrated to the more concentrated solution diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration until the

 concentration on both sides is equal Osmose The movement of water molecules through a thin membrane while leaving the dissolved salts behind, the process occurs in our bodies and is also a technical and commercial method of removing salts from saline water the passage of pure solvent from a solution of lesser to one of greater solute concentration, when the two solutions are separated by a membrane which selectively prevents the passage of solute molecules, but is permeable to the solvent A process of diffusion of a solvent such as water through a semi-permeable membrane which will transmit the solvent but impede most dissolved substances The normal flow of solvent is from the dilute solution to the concentrated solution The natural transport of water through a semi-permeable membrane which separates two solutions of different solute concentration The passage of a liquid from a weak solution to a more concentrated solution across a semipermeable membrane The membrane allows the passage of the solvent (water) but not the dissolved solids (solutes) This process tends to equalize the conditions on either side of the membrane The passage of a liquid from a weak solution to a more concentrated solution across a semiperm- eable membrane that allows passage of the solvent (water) but not the dissolved solids Diffusion of water through a membrane from a region of

 low solute concentration to one of higher concentration The process by which solvent molecules pass through a semipermable membrane from a dilute solution into a more concentrated solution A process of diffusion of a solvent (such as water ) through a semi-permeable membrane which will transmit the solvent but impede most dissolved substances The normal flow of solvent is from the dilute solution to the concentrated solution Osmosis is the process by which a liquid passes through a thin piece of solid substance such as the roots of a plant.

the processes of diffusion and osmosis If you say that people influence each other by osmosis, or that skills are gained by osmosis, you mean that this is done gradually and without any obvious effort. She allowed her life to be absorbed by his, taking on as if by osmosis his likes and dislikes. Spontaneous passage or diffusion of water or other solvent through a semipermeable membrane. If a solution is separated from a pure solvent by a membrane that is permeable to the solvent but not to the solute, the solution will tend to become more dilute by absorbing solvent through the membrane.

The pressure caused by the migration of solvent through the membrane is called osmotic pressure The movement of water across a selectively permeable membrane from a dilute solution (higher water concentration) to a more concentrated solution (See 61) The process by which a liquid passes from an area of low concentration through a semi-permeable membrane to an area of high concentration The passage of a liquid from a weak solution to a more concentrate solution across a semipermeable membrane that allows passage of the solvent (water) but not the dissolved solids the diffusion of water through a semipermeable membrane from an area of higher concentration of water to an area of lower concentration of water the flow or diffusion that takes place through a semipermeable membrane typically separating a solvent and a solution that strives to bring about a condition of equilibrium The spontaneous flow of water from a less concentrated solution to a more concentrated solution through a semipermeable membrane occurring until energy equilibrium is achieved The passage of a liquid from a weak solution to a more concentrated solution across a semipermeable membrane that allows passage of the solvent (water) but not the dissolved solids The process by which one component of a solution passes through a membrane to dilute the solution What is Osmoregulation?

| petMD What is Osmoregulation? How Fish Maintain an Internal Balance of Salt and Water Osmoregulation is the process of maintaining an internal balance of salt and water in a fish’s body. A fish is, after all, a collection of fluids floating in a fluid environment, with only a thin skin to separate the two. There is always a difference between the salinity of a fish’s environment and the inside of its body, whether the fish is freshwater or marine. Since the fish’s skin is so thin, especially around places like the gills, external water constantly tries to invade the fish’s body by osmosis and diffusion. Look at it this way: the two sides (inside and out) of a fish’s membrane skin have different concentrations of salt and water. Nature always tries to maintain a balance on both sides, so salt ions will move through the semi-permeable membrane towards the weaker salt solution (by diffusion), while the water molecules take the opposite route (by osmosis) and try to dilute the stronger salt solution.

Regardless of the salinity of their external environment, fish use osmoregulation to fight the processes of diffusion and osmosis and maintain the internal balance of salt and water essential to their efficiency and survival. Freshwater Fish In fresh water, the inside of a fish’s body has a higher concentration of salt than the external environment. Consequently, there is a tendency to lose salt and absorb water. To combat this, freshwater fish have very efficient kidneys that excrete water quickly. They also reabsorb salt from their urine before it is ejected to minimize losses and actively take salt from their environment using special cells in the gills. Marine Fish In marine environments, fishes face the opposite problem -- there’s relatively more salt and less water outside their bodies. Consequently, there is a tendency to take on salt and lose water. To combat this, marine fishes drink vast amounts of water and urinate little. Salt is a more complicated problem: special cells in the gills actively eliminate salt at the cost of extra energy and these fishes do not absorb any salt from the water they drink. Osmosis In Boats | TheYachtMarket Osmosis In Boats 17 October 2013 Will it cause my boat to sink?

Will my boat be unsaleble? The term "osmosis" often refers to a biological process where a liquid (usually water) passes through a semi permeable membrane. The water molecules pass through the membrane, but not the compounds dissolved in the water and the flow will be from the solution of lowest concentration towards that of higher concentration. In nature osmosis is used by plants to draw moisture and nutrients from the soil. The word was coined in the early 70s to describe the blistering found on many GRP (glass reinforced plastic) boats. GRP must be a close to perfect boat building material. It is relatively cheap, lightweight but strong, can be moulded into complex shapes and is almost maintenance free. Nevertheless osmosis can cause problems in GRP boats, although these are often not as great as the scaremongering and old wives tales would have you believe. In boats the membrane is a polyester gelcoat or epoxy paint and when the stronger solution draws solvent from the weaker one it becomes diluted and increases in volume and pressure, which leads to the familiar gelcoat blistering. The osmotic process can be reversed by applying greater pressure than the osmotic pressure, or by swapping the two solutions around.

But this does not answer all the questions: You may wonder how water can pass through a polyester gelcoat or epoxy coating when these materials are described as impermeable to water. The answer is that all paint coatings have minute gaps or holes in their molecular framework, allowing tiny quantities of moisture to pass through. Even though a brand new GRP hull is, in theory, chemically inert, it will still start to absorb moisture through the gelcoat as soon as it goes in the water. Very little damage will be caused at first, probably for the first two or three seasons. An epoxy resin may have a lifespan of ten or even twenty years if it is applied properly and not damaged. Eventually however, there can be a breakdown of the components within the gelcoat and while the hull may still appear to be in good condition, tiny amounts of moisture below it will be trying to destroy the laminate by breaking it down into its original constituents. These products will contain acids which give osmotic blisters their characteristic “vinegar” odour and will also add to “osmotic pressure”. While drying the boat out may provide a temporary reduction to moisture content, it will do nothing to remove the chemicals in solution which are the real cause of the problem.

Eventually the cycle of moisture absorption and laminate breakdown reaches the stage where moisture is absorbed more quickly than it can escape and that is when the gelcoat starts to blister. It usually happens slowly in small areas of the vessel’s bottom but will gradually increase. Localised treatment can be tried but this is only a temporary solution as it is likely that most of the vessel’s hull will be in a similar condition and will soon begin to show the tell tale blistering. Although osmosis does not cause de-lamination, the internal pressure caused by the osmotic process may separate poorly adherent layers from each other causing large swellings in the hull surface. The hull may also feel slightly soft when pressed firmly and may sound “dull” if tapped gently. The effects on your boat Will osmosis make it sink? While there are many horror stories of boats sinking on their moorings, or absorbing so much water they can hardly float, these are, on the whole, exaggerated. Gelcoats have very little mechanical strength but do provide a hardwearing exterior finish, helping to protect the structural laminate beneath it. Most of the absorbed moisture and solutes are confined to the layer directly behind the gelcoat.

The quantities of moisture involved are unlikely to have any adverse effect on buoyancy and the majority yachts can be sailed safely with their gelcoats completely removed. If there are symptoms of de-lamination, however, they must be investigated without delay. Treatment Osmotic blisters may vary in size from a pinhead to 10cm in diameter and will almost always be filled with fluid. This should be tested for acidity using pH papers and any reading between pH 0 to pH 6.5 suggests an osmotic condition. If the fluid has a sticky or greasy feel it indicates the presence of glycol, which must be completely removed in order to dry out the laminate and treat it. Sections of the gelcoat should also be removed in order to examine the laminate itself and find out how deeply seated the problem is. Some older boats may have as much as 5mm depth of the hull affected by osmosis. In these cases an expensive re-lamination may be the most sensible option. Although the well known saying, “a stitch in time saves nine”, is usually true, in the case of treatment of osmosis, early treatment often seems to be less successful than treatment of boats with advanced blistering.

This is because the breakdown process takes time and if treatment is carried out too early a reoccurrence of the problem is more likely to occur. Laminates are also easier to treat after a season afloat than after a long period out of the water. The main thing to remember is that the strength of your hull should not be endangered by letting the condition deteriorate too far. How Do I Go About It? The damaged or weak areas of laminate can be removed by abrasive grit blasting or slurry blasting. This process will not disturb the surrounding sound areas of the boat. Blasting will produce an excellent surface with good adhesion properties for paint coatings. Unfortunately blasting is a messy and slow job which has been heavily restricted in many marina complexes. It may also produce an uneven hull profile which may need filling. Another method is to use gelcoat peelers, which are comparatively quick and clean and produce a smooth hull profile. This method too has its disadvantages. It only removes a pre-set thickness of material, so may not remove all the suspect areas. It also means that the smooth surface produced may make drying and removal of solutes more difficult.

Probably the best compromise is to use a gelcoat peeler first, to remove the majority of unwanted gelcoat and laminate and follow up with some moderate grit blasting to prepare the surface, using a pressure washer with a suitable attachment. Grinding is another method, useful for preparing small areas, but its disadvantage is that it produces large quantities of dangerous dust, so respiratory protection must be worn. Heat guns should NOT be used as they might result in distortion and de-lamination, especially if the hull is wet. Heating GRP can also generate toxic fumes, especially if old antifouling is present. After preparing the surface of the hull, the next stage is to dry it out, preferably in natural conditions, making sure that the bilges are also dry and well ventilated. Taking moisture readings may help to confirm that the hull is dry enough to treat. Solvent free epoxies are the usual recommended initial coating for bare laminates as they avoid the risk of solvent retention and have good impregnation and adhesion properties. They can also be used for subsequent coats and you can apply a new coat as soon as the previous one is tacky.

You may however prefer to use a solvent containing gelshield which has a better tolerance to lower temperatures, more flexible over-coating times and good performance where moisture permeability is concerned. If you are applying antifouling as well make sure that you use materials which are compatible. Some antifoulings have poor adhesion to epoxy coatings. Finally Beware of believing everything you hear down at the harbour or read on the internet, such as: Boats don’t get osmosis. It will go away by itself. It’s just a slight humidity problem. Your boat could sink. You won’t be able to sell it. It only happens in old boats ...etc. My advice is – don’t panic when you see the first blisters appear. Monitor them, test them, get advice from someone reliable, who you can trust and who knows their boats. When you decide that the time is right to treat the patient, do a thorough job, don't skimp it or go for the cheapest option. Author – Dee White

Question: What is the name of the process, in which a fluid passes through a semi-permeable membrane, from a weaker to a stronger solution?
Answer: OSMOSIS