Reverse osmosis, often abbreviated to RO is a purification procedure that uses membrane technologies to filter and purify liquids. Reverse osmosis is now commonly used around the world for the treatment and purification of water used for drinking (potable water) and industrial processes.
Reverse osmosis makes use of a semipermeable membrane to separate unwanted materials found in the raw water (solute). These materials can include salts and minerals, bacteria and other contaminants.
As the solute passes through the RO membrane it filters out larger unwanted materials including ions and molecules, to create a pure solution that is free of specified contaminants.
How does Reverse Osmosis Work?
Reverse osmosis is a natural process and occurs when two solutions or solvents are separated by a semipermeable membrane.
Whilst under a pressure greater than the osmotic pressure the two solutions will pass through the membrane, from high to low concentration to create a chemical equilibrium. The solute and its contaminants are retained on the pressurised side of the membrane, the pure solution on the other.
Applications for Reverse Osmosis
RO is now used extensively in commercial, process and industrial environments all around the World.
It was originally inspired by the way sea birds get fresh water to drink. They have a membrane in their throat that repels the salt contained in the sea water and enables them to essentially filter out fresh water so they can safely drink.
Humans replicated the process several decades ago and it is now used to remove salt from sea water (desalination) to create potable water for drinking purposes. It is also commonly-used in a wide range of industrial, commercial and process applications where purified water or liquid filtration at a molecular level is required.
Reverse Osmosis Membranes
Typical membranes used in reverse osmosis processes are much like cellophane. A degree of pressure is applied to the solution on the side of the water (solute) to be cleaned or filtered. The water is then pushed through the RO membrane while any impurities are left on the other side. This means the water pushed through will be cleansed through the reverse osmosis process, and the impurities are separated out.
Common RO Membrane Materials
A variety of materials are commonly used to create a typical reverse osmosis membrane that works in such situations. For example polyamide thin film composites are often used, as are cellulose triacetate.
Two types of RO membranes are commonly used – either spiral wound membranes or hollow fibre ones.
Hollow fibre membranes tend to have a larger capacity but they also have a greater chance of becoming blocked. Thus while the process of reverse osmosis is in theory quite simple to understand, it involves several scientific and engineering elements that are more complex than you may think.
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