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Reverse osmosis
- 2. Reverse Osmosis • 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. How does Reverse Osmosis (RO) work?
- 3. 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.
- 4. This 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. •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.
- 5. • Reverse Osmosis is the process of Osmosis in reverse. • 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.
- 6. This 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.
- 7. 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.
- 8. • 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. • 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.
- 9. 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 • 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
- 10. • Likewise, the greater the ionic charge of the contaminant, the more likely it will be unable to pass through the RO membrane, this is why an RO system does not remove gases such as CO2 very well because they are not highly ionized and have a very low molecular weight. • Reverse Osmosis is very effective in treating brackish, surface and ground water for both large and small flows applications.
- 11. Dependent on the following factors • Influent solute concentration • Water Flux Rate • Pressure . Pressure caused by the difference in solute concentration between the two compartments . The externally applied pressure • Required Pressure Amount (high concentrated side): . For fresh and brackish water: 15.5 to 26 bar . For seawater: 55 to 81.5 bar
- 12. Desalination • Useful for areas that have either no or limited surface water or ground water • Reverse osmosis is the most common method of desalination, although 85 percentage of desalinated water is produced in multistage flash plants. • Sea Water Reverse Osmosis (SWRO): No heating or phase changes are needed, energy requirements are low in comparison to other processes of desalination, but are still much higher than those required for other forms of water supply • The Ashkelon seawater reverse osmosis(SWRO) desalination plant in Israel is the largest in the world.
- 13. Applications • Desalination of brackish water • Desalination of seawater • Production of ultrapure water • Wastewater treatment
- 14. RO disadvantages • Household RO units use a lot of water because they have low back pressure • As a result they recover only 5 to 15 percentage of the water entering the system • The remainder is discharged as waste water • An RO unit delivering 5 gallons of treated water per day may discharge 40 to 90 gallons of waste water per day to the septic system • Large scale industries/municipal systems have a production efficiency of closer to 48% because they can generate the high pressure needed for RO filtration.
- 15. Video