Reverse Osmosis

What Is It, Exactly?
Before discussing reverse osmosis, we should probably go over what osmosis is first.  Osmosis is the movement of molecules through a semi-permeable membrane of some sort from a low water-potential area to a high water-potential area.  For example, when a person drinks salt water, osmotic pressure in the body draws water away from other places and into the stomach to desalinate the water, causing severe dehydration and eventually death.  That sounds horrible, but there’s a positive to this, and it comes in the form of reverse osmosis.
Reverse osmosis is a type of filtration method that applies pressure to a solution when it’s on one side of a semi-permeable membrane, forcing it to the other side.  In the process, various impurities are trapped in the membrane, with the end result being cleaner water.  This process is highly effective when desalinating salt water to make it safe to drink, hence the example in the first paragraph.  While the process is similar to membrane filtration, there are a couple of differences.  First, membrane filtration acts almost like a sieve, with water passing through and the various impurities getting caught on the membrane.  However, reverse osmosis acts more like an air filter, in that the water is being pressured through the membrane to the other side.
This process’s most applicable use is in drinking water purification.  Activated carbon is often used as a filter to eliminate chlorine and other such chemicals, followed by flowing through a semi-permeable membrane.  The membrane is usually made out of polyimide.  Afterward, the water may be sent through another activated carbon filter to eliminate anything that may have slipped through the membrane.  For secondary disinfection purposes, ultraviolet light can be used to kill viruses and bacteria.  When used in tandem with UV disinfection, reverse osmosis can create highly purified water.
Purifying water isn’t the only place reverse osmosis can be used.  As mentioned before, it is very effective in desalinating water, and this is important in places where there is no fresh water source available, like Saudi Arabia for example, which is surrounded by salt water.  Saudi Arabia has several desalination plants to provide its people with clean drinking water.   It can also be used in irrigation, concentrating juices, car washing (because of the low mineral content), and aquariums.  It can also be used in places where water is actually considered an impurity, such as in ethanol production.

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