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Can Salt Water Be Purified by a Reverse Osmosis?

Reverse osmosis not only purifies saltwater, but was originally developed specifically to remove salt from water. When researchers discovered that this process could also decontaminate water, they began using it as a method to purify water for home use, since the process removes a variety of contaminants in mineral form. The process is unfortunately very inefficient.

Basics
- In the reverse osmosis process, there are three kinds of water: saline feed water, low-salt water and reject water, also called brine. Saline feed water is the ocean water that people want to desalinate. The low-salt water is the product created by reverse osmosis. The reject water is the more salty water left behind.
Pretreatment
- Before sending the water through the membrane -- a filter for removing salt -- the reverse osmosis system must remove solids, adjust the pH and add threshold inhibitors to prevent scaling in the pretreatment phase before pressurization commences.
Pressurization
- Pressurized water is forced through a membrane that only allows water and some other particles through. Osmosis is the tendency of water to travel from a weaker saline solution to a stronger solution, causing salt to become evenly distributed throughout the water. Salt molecules are larger than water molecules, so the membrane allows water molecules to pass through, while blocking salt. This creates a concentration of high-salt water and one of low-salt water. The water normally doesn̵7;t want to flow through the membrane, due to osmosis. However, the pressure forces the water through. The need for pressurization makes reverse osmosis not very energy efficient, requiring 800 to 1,000 psi. The water is pressurized in a closed container. Water from the very concentrated brine solution must be removed periodically and replaced with newer seawater or the amount of pressure needed to force the water through the membrane will increase, subsequently increasing the amount of energy needed to operate the system.
Product
- The membrane does not remove all the salt. Some remains in the low-salt water product. This product must be further treated before the water is safe to drink. The water must also have its pH raised from five to seven.
Utility
- Reverse osmosis is a very inefficient way to filter water, wasting three gallons of water for every one gallon purified. People cannot drink seawater because of osmosis. Drinking seawater leads to dehydration, since the salt draws the water to it, reducing the amount of water in the body. Therefore, reverse osmosis is helpful in coastal communities, which have almost unlimited amounts of water and can easily dispose of the reject water.

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