Reverse Osmosis Desalination: Definition, Process, and Advantages

Reverse osmosis desalination represents a process through which water gets purified. The water purification technology uses a semipermeable membrane that helps to remove large particles, molecules, and ions from drinking water. Specialists use an applied pressure to surpass osmotic pressure. Reverse osmosis is able to remove several different types of suspended and dissolved species in the water, including bacteria. Specialists use it both in the production of potable water and industrial processes.

Some animals are also able to use reverse osmosis to desalinate seawater, possessing a membrane in their throats that separates water molecules from salt. In this way, they are able to drink fresh water, spitting out the salt. This is a specific feature of seabirds. Nevertheless, we have also figured out how to develop this process about 40 years ago. Now, we use reverse osmosis in medicine and other industries to learn how to purify water and other solvents, separating them from several other components.

Recently, reverse osmosis desalination has been used for making Water for Injection and water for dialysis in hospitals.

The process of reverse osmosis desalination

Reverse osmosis is a difficult process, using a membrane under pressure to divide relatively pure water from a less pure solution. Osmotic pressure triggers the separation of two aqueous solutions which have different concentrations via a semi-permeable membrane. Hence, water passes through that membrane in the direction of the solution which is more concentrated. The water flow will reverse in case enough counter pressure applies on the concentrated solution to surpass the osmotic pressure.

Water molecules can develop hydrogen bonds via reverse osmosis and remain in the membrane matrix. Hence, the water molecules which enter the membrane via hydrogen bonding can be pushed using under pressure. When this process is utilized, most of the organic substances which have a molecular weight that surpasses 100 are separated. The organic substances are viruses, bacteria, pyrogens, and oils.

On the other hand, the ions of salt get rejected via a mechanism which is connected to the valence of the ion. Dielectric interactions help to reject ions. Furthermore, ions which have higher charges get repelled to a larger distance from the membrane surface. Usually, these membranes are made from polyamide, polysulfone and cellulose acetate.

The membrane is made up of skin which measures 0.25 microns. It also features a support layer that measures 100 microns. The membrane represents an active barrier, allowing the water to get through.

The quality of water after reverse osmosis desalination

Reverse osmosis triggers a constant amount of dissolved solids in water, similar to the amount of those in the feed water. A reverse osmosis system design relies on a particular range of feed water total dissolved solids, indicating the percentage of recovery and the one of rejection desired. The quality of product water depends on the percentage of recovery and the one of rejection.

A desalination plant revealing part of its equipment

Even if this is useful, managing a desalination plant is very expensive because of the equipment.

The advantages of reverse osmosis desalination

  1. Potable water

The process of desalination offers people potable water. This process helps to remove minerals and dissolved salts from seawater. Hence, seawater transforms into freshwater which is ideal for drinking. That is why this can be a suitable process that people can use in many areas around the world which experience droughts.

  1. Water for the agricultural industry

Desalination also helps farmers produce water appropriate for irrigation, being extremely helpful in arid areas or regions experiencing droughts. Hence, farmers and people working in the agricultural industry would be able to produce their own crops, and they will not depend on imports, improving their economy. Furthermore, the residents in those areas will have enough food, keeping hunger away.

  1. Tried-and-tested technology

This process of water purifying is different from other similar processes because it has surpassed the research stage. Therefore, specialists consider it a reliable, workable and safe process which they have tried and tested in numerous applications.

The disadvantages of reverse osmosis desalination

  1. Consumes a lot of energy

This useful process consumes a high amount of energy, without being a feasible solution to water supply problems. We would waste a lot of water to develop this process, and this would not be energy efficient. For instance, distillation also requires boiling millions of gallons of saltwater at very high temperatures to transform it into potable water. However, reverse osmosis desalination uses huge amounts of energy to overcome the process of natural osmosis and annihilate large particles from seawater through a membrane.

  1. The costs can be high

The maintenance of desalination plants can be really expensive since the machines and the equipment they use cost between $3000 million to about $3 billion. Furthermore, they also require the use of massive amounts of energy to develop the desalination process. Experts argue that desalinated water is five times more expensive when harvesting it compared to freshwater.

  1. It is not eco-friendly

The process of reverse osmosis desalination is harmful to the environment because it removes salt from water and specialists dispose that salt somehow. Hence, the disposal of that salt constitutes pollution. The most crucial problem in this situation is that other chemicals like chlorine are present in the water during the process. When this gets back into the water, it can harm numerous marine ecosystems, affecting the marine creatures due to the chemicals.

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Summing up

Since desalination has both advantages and disadvantages, it is important to consider all of them before you invest in this water purification system. Nowadays, protecting the environment is extremely important for us since the effects of climate change become even more harmful as the days go by. Hence, it is important to save up on our natural resources, recycle and avoid pollution to be able to live in a healthy environment.

However, this process of reverse osmosis desalination can be extremely useful in countries where residents have to cope with severe droughts and where the few water resources are not potable. The desalination process will kill all the bacteria and microbes in the water, transforming it into a potable source.

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William E. Eubanks

I'm one of the main writers on the site; mostly dealing with environmental news and ways to live green. My goal is to educate others about this great planet, and the ways we can help to protect it.

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