Reverse Osmosis System Reverse Osmosis System Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be "selective," this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely. In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (High Water Potential), through a membrane, to an area of high solute concentration (Low Water Potential). The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, there are key differences between reverse osmosis and filtration.
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The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Reverse osmosis, however, involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure, and water flux rate. Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other substances from the water molecules. Osmosis Definition :- Just as a gas can diffuse into vacant space or another gas, a solute can diffuse from a solution into the pure solvent. If you pour a saturated aqueous solution of potassium permanganate with the help of a thistle funnel into a beaker containing water, it forms a separate layer at the bottom. Osmosis is a process by which the solvent molecules will pass through a semipermeable membrane from the less concentrated part (solute concentration) to the more concentrated (solute) solution. A semipermeable membrane, usually an animal membrane, allows only the solvent particles and not the solute particles inside it, due to the pore size. Osmosis is also a phenomenon like diffusion. Osmotic Pressure Definition :- The excess pressure which must be applied to a solution to prevent the flow of the solvent into it through a semipermeable membrane is known as the osmotic pressure of the solution. Osmosis Membrane :- The semipermeable membranes used in the osmosis process can be an animal membrane, paper, etc. It should allow only the solvent particles and not the larger solute particles. Preparation of semipermeable membrane :- Parchment paper and the animal bladder mentioned above are not truly semipermeable. Traube, a German chemist, found that films of certain gelatinous precipitates, especially of cupric ferrocyanide, Cu2 [Fe(CN)6], are perfectly semipermeable to sucrose.
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Prefer using copper ferrocyanide membrane for a number of quantitative measurements to calculate the osmotic pressure. The membrane is usually deposited in the walls of a porous pot. The porous pot is first thoroughly washed and dried and then filled with a solution of copper sulphate and immersed in a solution of potassium ferrocyanide. Diffusion of ions takes place through the pores where cupric and ferrocyanide ions meet in the walls of the pot, a gelatinous precipitate of copper ferrocyanide is formed. Hypotonic Solution :- Consider two solutions in contact with each other through a semipermeable membrane. If solution A has a lower osmotic pressure than solution B, then on comparison, such solutions are hypotonic in nature. Applying this to red blood cells, if the fluid outside the red blood cells have less osmotic pressure than that of inside the red blood cells, such situation is termed as Hypotonicity or hypotonic solutions. Forward Osmosis :- Forward Osmosis is a normal osmosis process used in water purification, desalination process, etc. Here, a solution of higher solute concentration is allowed to flow with the process into a solution of lower concentration. It is a new field of research. Water is separated from the unwanted particles using this process. Unlike reverse osmosis where a lot of outside pressure is applied, this process does not need external pressure source.
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