How Does Reverse Osmosis Work to Purify Water

It is ironic how even though we’re surrounded by seas and oceans, there are parts where people don’t have enough clear portable water for their everyday needs. If only we could somehow purify all that seawater and use it! Well, thanks to technology, now we can.

Reverse osmosis is one of the simplest water treatment processes for desalinating the sea water. A simple yet effective solution, RO process distills the seawater and gives us pure drinking water whenever required.

In reverse osmosis, the liquid is strained through a membrane that is selectively permeable allowing only water molecules to pass through and stopping everything else. Read on to know more about RO and how does reverse osmosis work to purify water:

Need For Reverse Osmosis

Water scarcity issues aren’t just limited to the third world countries. Blame it on global warming or the excessive pollutants floating around in the environment, the fact remains that water shortage is fast turning out to be a serious global threat.

Many companies and water treatment plants are adopting RO or reverse osmosis for purifying contaminated water making it fit for human consumption. The process was naturally developed in most seabirds that have a membrane in their throat for separating the water molecules from the salt. Humans have been using the same process for about 40 years now for the same purpose – to desalinate water.

Reverse osmosis is also used in the water filters and purifiers found at most homes for distilling the water and removing the harmful solvents and particles. Today, the process is also used in hospitals for making pure water for dialysis.

reverse osmosis system

How Does Reverse Osmosis Differ from Osmosis?

Assuming that you are familiar with the term “reverse”, let us throw some light on the process of osmosis and then club the two terms to get a better idea of the entire RO process. Osmosis is basically the passage or diffusion of water molecules through the semi-permeable membrane that blocks particles and dissolved solutes that are otherwise present in the water. The solution moves from low concentration area to a high concentration area passing through a barrier due to the surrounding osmotic pressure.

In reverse osmosis, the process is tweaked a little bit. Instead of using osmotic pressure, we apply a colligative thermodynamic pressure to overcome it. The process removes almost 90% of the dissolved solvents and microscopic bacteria making water potable and pure again.

ro water purifying process

The Science Behind Reverse Osmosis

Reverse osmosis is the process by which you can desalinate and restore water’s purity. In the process the solution is made to pass through a semi-permeable membrane. Now, when two aqueous solutions of different concentration are made to pass through a barrier, it will flow towards the solution that has a higher concentration.

In RO this flow is reversed by applying a counter force that’s strong enough to oppose the osmotic pressure. The liquid is pushed though the membrane to form a less concentrated solution. Water molecules can fit into the membrane matrix as they form hydrogen bonds in the reverse osmosis process. However, organic and soluble particles and organisms with a molecular weight of over 100 are directly sieved out.

Salt ions, though small enough to pass through the membrane, are rejected because of their high valence. The salt ions are repelled from the surface of the membrane due to their electric charge. About 85-95% of the ionic salts are flushed out this way. Portable water purifiers, filters and other water treatment methods use RO for desalinating and clearing the water from bacteria, dust and other particles.

RO filtering water

Is the Water Quality Any Better?

Most of the artificial membranes made for RO purification are made of cellulose acetate, polysulfonate, and polyamide. This sieve of sorts is pretty thin and has hundreds of holes as tiny as 0.0001 microns that only allow water to pass through. Now, most of the soluble particles and pollutants are segregated straight away however a small percentage still remains. The reverse osmosis removes almost 90-95% of pollutants from the water. Most RO systems have a fixed limit of feed water TDS for determining the amount of water rejected and recovered during the process. A high recovery percentage and low rejection rate has a direct impact on the quality of water.

The Bottom Line

It is alarming how the overall temperature of earth has suddenly shot up contributing to the climate changes around the world. While some areas are flooded, others face an acute water shortage creating drought-like conditions. Water conservation is one of the most pressing issues of the world today. Treatment methods such as reverse osmosis and other desalination techniques offer a quick and affordable solution to the problem. The water purified from a RO system tastes a lot sweeter, purer and is healthier than normal tap water.

1 Comment
  1. Reply
    Raj Kumar November 22, 2017 at 7:16 am

    RO is a good technology for water purification. It purifies the water very well from bacteria, dust, sand, etc. But it also removes the essential minerals from the water. So only RO water is also not good for drinking. The best water for drinking is that which filtered with RO and UF, treated with UV and get Alkaline characteristics.

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