Reverse Osmosis – Answers to the Top 20 Asked Questions:

Reverse osmosis (RO) is a separation process that uses pressure to force a solution through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute.

The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases the membrane is designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions). This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2-17 bar (30-250 psi) for fresh and brackish water, and 40-70 bar (600-1000 psi) for seawater, which has around 24 bar (350 psi) natural osmotic pressure which must be overcome.

This process is best known for its use in desalination (removing the salt from sea water to get fresh water), but it has also been used to purify fresh water for medical, industrial and domestic applications since the early 1970s. When two solutions with different concentrations of a solute are mixed, the total amount of solutes in the two solutions will be equally distributed in the total amount of solvent from the two solutions.

Instead of mixing the two solutions together, they can be put in two compartments where they are separated from each other by a semipermeable membrane. The semipermeable membrane does not allow the solutes to move from one compartment to the other, but allows the solvent to move. Since equilibrium cannot be achieved by the movement of solutes from the compartment with high solute concentration to the one with low solute concentration, it is instead achieved by the movement of the solvent from areas of low solute concentration to areas of high solute concentration. When the solvent moves away from low concentration areas, it causes these areas to become more concentrated. On the other side, when the solvent moves into areas of high concentration, solute concentration will decrease. This process is termed osmosis. The tendency for solvent to flow through the membrane can be expressed as “osmotic pressure”, since it is analogous to flow caused by a pressure differential.

In reverse osmosis, in a similar setup as that in osmosis, pressure is applied to the compartment with high concentration. In this case, there are two forces influencing the movement of water: the pressure caused by the difference in solute concentration between the two compartments (the osmotic pressure) and the externally applied pressure.

The human body is anywhere from 55% to 78% water depending on body size. To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though most advocates agree that 67 glasses of water (approximately 2 litres) daily is the minimum to maintain proper hydration. Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather. For those who have healthy kidneys, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) it is dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication (hyperhydration), which can be fatal. The “fact” that a person should consume eight glasses of water per day cannot be traced back to a scientific source.[There are other myths such as the effect of water on weight loss and constipation that have been dispelled.

An original recommendation for water intake in 1945 by the Food and Nutrition Board of the National Research Council read: “An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods.” The latest dietary reference intake report by the United States National Research Council in general recommended (including food sources): 2.7 liters of water total for women and 3.7 liters for men. Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. According to the Institute of Medicinewho recommend that, on average, women consume 2.2 litres and men 3.0 litresthis is recommended to be 2.4 litres (approx. 9 cups) for pregnant women and 3 litres (approx. 12.5 cups) for breastfeeding women since an especially large amount of fluid is lost during nursing. Also noted is that normally, about 20 percent of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

Humans require water that does not contain too many impurities. Common impurities include metal salts and/or harmful bacteria, such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.[29] The single largest freshwater resource suitable for drinking is Lake Baikal in Siberia, which has a very low salt and calcium content and is very clean.

The human body is anywhere from 55% to 78% water depending on body size. To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though most advocates agree that 67 glasses of water (approximately 2 litres) daily is the minimum to maintain proper hydration. Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather. For those who have healthy kidneys, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) it is dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication (hyperhydration), which can be fatal. The “fact” that a person should consume eight glasses of water per day cannot be traced back to a scientific source.[There are other myths such as the effect of water on weight loss and constipation that have been dispelled.

An original recommendation for water intake in 1945 by the Food and Nutrition Board of the National Research Council read: “An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods.” The latest dietary reference intake report by the United States National Research Council in general recommended (including food sources): 2.7 liters of water total for women and 3.7 liters for men. Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. According to the Institute of Medicinewho recommend that, on average, women consume 2.2 litres and men 3.0 litresthis is recommended to be 2.4 litres (approx. 9 cups) for pregnant women and 3 litres (approx. 12.5 cups) for breastfeeding women since an especially large amount of fluid is lost during nursing. Also noted is that normally, about 20 percent of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

Humans require water that does not contain too many impurities. Common impurities include metal salts and/or harmful bacteria, such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.[29] The single largest freshwater resource suitable for drinking is Lake Baikal in Siberia, which has a very low salt and calcium content and is very clean.

Ultraviolet disinfection is a form of wastewater treatment. It is commonly used in garden pond filtration systems to kill algae. UV is also used for treatment of water after it leaves a Reverse Osmosis Holding Tank.

Large scale urban UV wastewater treatment is performed in cities such as Edmonton, Alberta.

UV Dosing
One method for gauging UV effectiveness is to compute uv dose. The U.S. EPA publishes UV doseage guidelines

Doseage involves the following parameters:

• flow rate (reflecting contact time)
• transmittance (reflects light reaching the target)
• turbidity (“cloudiness”)
• lamp age (reflects reduction in UV intensity)
• lamp fouling
• % active lamps (reflects lamp outages in each lamp bank)

Water purification is the process of removing undesirable chemical and biological contaminants from raw water. The goal is to produce water fit for a specific purpose. Most water is purified for human consumption (drinking water) but water purification may also be designed for a variety of other purposes, including to meet the requirements of medical, pharmacology, chemical and industrial applications. In general the methods used include physical process such as filtration and sedimentation, biological processes such as slow sand filters or activated sludge, chemical process such as flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light.

The purification process of water may reduce the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses, fungi; and a range of dissolved and particulate material derived from the minerals that water may have made contacted after falling as rain.

The standards for drinking water quality are typically set by Governments or by international standards. These standards will typically set minimum and maximum concentrations of contaminants for the use that is to be made of the water.

It is not possible to tell whether water is of an appropriate quality by visual examination. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all the possible contaminants that may be present in water from an unknown source. Even natural spring water – considered safe for all practical purposes in the 1800s – must now be tested before determining what kind of treatment, if any, is needed. Chemical analysis, while expensive, is the only way to obtain the information necessary for deciding on the appropriate method of purification.

According to a 2007 World Health Organization report, 1.1 billion people lack access to an improved drinking water supply, 88% of the 4 billion annual cases of diarrheal disease are attributed to unsafe water and inadequate sanitation and hygiene, and 1.8 million people die from diarrheal diseases each year. The WHO estimates that 94% of these diarrheal cases are preventable through modifications to the environment, including access to safe water. Simple techniques for treating water at home, such as chlorination, filters, and solar disinfection, and storing it in safe containers could save a huge number of lives each year.

Trinitrate and Nitrogen Trioxide redirects here. See also glyceryl trinitrate. For the film stock see nitrocellulose.

An electrostatic potential map of the nitrate ion. Areas colored red are lower in energy than areas coloured yellow. The oxygen atoms carry the majority of the negative charge.

The structure and bonding of the nitrate ion. The N-O bonds are intermediate in length and strength between a single bond and a double bond.

In inorganic chemistry, a nitrate is a salt of nitric acid with an ion composed of one nitrogen and three oxygen atoms (NO3-). In organic chemistry the esters of nitric acid and various alcohols are called nitrates.

Chemical properties
The nitrate ion is a polyatomic ion with the empirical formula NO3- and a molecular mass of 62.0049. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by bcanonical structures of the nitrate ion are shown resonating below:

Almost all inorganic nitrate salts are soluble in water at standard temperature and pressure.

In organic chemistry a nitrate is a functional group with general chemical formula RONO2 where R stands for any organic residue. They are the esters of nitric acid and alcohols formed by nitroxylation. Examples are methyl nitrate formed by reaction of methanol and nitric acid,[1] the nitrate of tartaric acid,[2] and the inappropriately named nitroglycerin.

Related materials
Nitrates should not be confused with nitrites, (NO2-) the salts of nitrous acid. Organic compounds containing the nitro functional group (which has the same formula and structure as the nitrate ion save that one of the O- atoms is replaced by the R group) are known as nitro compounds.

Human toxicity
High levels of nitrates, most often through occupational exposure in adults, are toxic to humans. Nitrates oxidize the iron atoms in hemoglobin from Ferrous Iron (2+) to Ferric Iron (3+), rendering it unable to carry oxygen. This condition is called methemoglobinemia and can lead to a lack of oxygen in tissues. Methemoglobinemia is treated with methylene blue. Infants, in particular, are especially sensitive to methemoglobinemia as a result of nitrate exposure. This is most often caused by high levels of nitrates in drinking water.

Marine toxicity
In freshwater or estuarine systems close to land, nitrate can reach high levels that can potentially cause the death of fish. While nitrate is much less toxic than ammonia or nitrite,[3] levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species.[citation needed] However, in light of inherent problems with past protocols on acute nitrate toxicity experiments, the extent of nitrate toxicity has been the subject of recent debate.[4]

In most cases of excess nitrate concentrations in aquatic systems, the primary source is surface runoff from agricultural or landscaped areas which have received excess nitrate fertilizer. These levels of nitrate can also lead to algae blooms, and when nutrients become limiting (such as potassium, phosphate or nitrate) then eutrophication can occur. As well as leading to water anoxia, these blooms may cause other changes to ecosystem function, favouring some groups of organisms over others. Consequently, as nitrates form a component of total dissolved solids, they are widely used as an indicator of water quality.

Nitrates are also a by-product of septic systems. Specifically, they are a naturally occurring chemical that is left after the break down or decomposition of animal or human waste. Water quality may also be affected through ground water resources that have a high number of septic systems in a watershed. Septics leach down into ground water resources or aquifers and supply near by bodies of water. Lakes that rely on ground water are often affected by nitrification through this process.