The Reverse Osmosis: The Water Purifying Method Where Pressure Meets Osmosis

I would be taking about fresh water today and it is only natural I start from my country where everyone is their own water producer. There is a popular water product referred to as pure water that is sold in plastic sachets. I decided to visit a plant where it is produced.



^{Picture of the pure water in plastic sachets packed on the factory}
These sachets end up in landfills and since they do not decay that fast cause a sort of environmental pollution. But ever since 1993 that it became popular in Nigeria there is just no going back from demand and consquent use.

On our way to the factory, the driver couldn't help but buy some to quench his thirst as the sun was high.

^{Driver buying water from a street hawker}

We finally arrived and was greeted by this eight (8) number of plastic water storage tank, each has a capacity of at least 2000 litres standing on an iron stand on the premises of this water factory. Here is where the water is stored before being moved to the factory for onward processing.



^{Overhead Tanks}

The water is sourced from underground and here is the submersible pump that is used to transport it from a distance of at least 100 ft to the overhead tank

^{Submersible Pump. The rope is there to help pull it out of the depth of the borehole for servicing and repairs}

We entered inside and met these gleaming tanks which we were told is the bottle cleaning machine. Notice the surface pump there, it connects to one of the overhead tanks outside.

^{Automatic Bottle Washing Machine}
A little further down I met the reverse osmosis machine which I would talk about in greater deal below.

^{Reverse Osmosis Machine Control blinking red and green light}

Due to unavailability of good drinking water in this part of the country and the inefficient and underfunded water board. It becomes apparent to the majority of the populace that if they should avoid ailments that can result from consuming contaminated water, they must resort to self-treatment of their drinking water.

But unfortunately, this is not easy to come by as it comes at a considerable cost. Individuals, resort to buying sachet water popularly known as ‘pure water in Nigeria. These pure water are not necessarily pure because they do not produce most of them under strict adherence of the regulatory agency called NAFDAC. To the ordinary man, what makes the water ‘pure’ is its packaging in fanciful transparent polythene. At every corner, you will notice adults and even underage that is supposed to be in school hawking these waters. They package it 20 in a pack.And due to lack of electricity to chill the water, they take it to cold rooms where they pay for it to be frozen before they commence sales. The problematic aspect of the hawking is that you must speed up the sales before the hot weather returns it to warm water which will put them at massive loss as they paid already for the freezing. That implies that the hawking must take place in densely populated locations with traffic gridlock to facilitate speed in sales before you have it hot again. The average temperature here is 30 degrees Celsius, and keeping it cold within the duration of sales is one of the problems that come with the hawking.

The Earth is covered by about 71 percent water, out of this percentage the ocean holds about 96.5 percent of the water. You know when you mention ocean and water the next thing that comes to mind is salt. We desalinate the water to make it drinkable, by removing the sal. Going by this statistics, the earth has only a miserly 3.5% of safe drinking water.

These freshwater are not immediately available because it freezes to form glaciers and ice. If somehow it melts, the sea level would shoot up to 2.7km. At least, for now, the glaciers and ice have not decided to melt and flood the earth with water, the available water is 0.7% of the total water in the universe that are free-flowing.

Every day we drink water from various sources, most of the water comes from sources which include waterboard that treats the water with chlorine, some are from factories that used one form or filtration (water treatment) or another. They usually guarantee that it is 100% "safe" for drinking as it had undergone reverse osmosis. The word sounds very mysterious and somewhat bogus. Let us find out what it is.

But before we do do that we may have to find out what osmosis is. Then we would look at what happens when we reverse it.

Back in school, we have people that go to night classes with about six textbooks all the size of a mini pillow, but unfortunately, it turns out they use it for a pillow when they break down when sleep insistently calls. We jokingly say they are trying to transfer the knowledge in the concentrated solution (book) to the less dense matter (their brain) through osmosis. Of course, it doesn't work as I would have been at the forefront of it if it does.

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I think it is safe from on here to assume that we have an idea what osmosis was, let us walk back from the road we came from and do a reverse of it. Shall we? Yes, let us go.

In osmosis, there is flow from solutions of low concentration to that of high concentration. This process continues until both are of the same concentration.

In reverse osmosis, salty water (high concentration) is made to flow through a semi-permeable membrane through the application of external pressure of up to 60 bars for desalination to take place. While osmosis occurs naturally, the reverse does not.

Simply defined, osmosis is when two solvents that are not the same but are in close contact, but separated by a selective layer ( a semi permeable membrane) that allows certain molecules right of passage, mix together until the two are near alike.

This movement occurs from the side with less or low concentration (pure water as in the example above) to the side with more or high concentration (salt water).

This osmotic property explains the reason we get thirsty when we enjoy the salty foods. The high presence of salt molecules draws water away from the body's cell and hence making us dehydrated.

The solute would move through the semipermeable membrane to the side with more concentration of dissolved compound until we reach an equilibrium.

This difference in the water pressure, which makes the pure water to move to the salt water, is known as the osmotic pressure.

Once the pressure between the two solvents are the same, osmosis is said to be at equilibrium.

^{Wikipedia Creative Commons: A diagram showing the Osmotic Process}
where
P1= Osmotic pressure in low concentration solution
P2= Osmotic pressure in low concentration solution
Δπ= Osmotic pressure differential


I think it is safe from on here to assume that we have an idea what osmosis was, let us walk back from the road we came from and do a reverse of it. Shall we? Yes, let us go.

In osmosis there is flow from solutions of low concentration to that of high concentration. This process continues until both are of same concentration.

In reverse osmosis, a salty water (high concentration), or an impure water filled with bacteria, or any other impurities, is made to flow through a semi-permeable membrane through the application of external pressure of up to 60 bars for desalination to take place. The pressure chosen is dependent on the type of water in view. While osmosis occurs naturally, reverse does not.

This pressure overrides the osmotic pressure and pushes the salty sea water through a semi-permeable membrane with the ability to allow only the smaller water molecules while trapping, the bigger salt molecules. Thus leaving the salt behind and pushing the fresh water to the other side.

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Reference

• Earth's Water
• Desalination
• Reverse Osmosis
  Osmosis Gif from Ghiphy.com

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