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Publié : 24 mai 2012

How can reverse osmosis, powdered water and fog nets contribute to solve water problems on Earth ?

On Earth, 97% of the water is saltwater. This water can’t be consumed by humans who have to do with the remaining 3%. But even in these 3%, 2% are ice. There’s only 1% of the earth water that can be consumed by humans.
That’s why freshwater is a problem on earth. We can’t survive without water, it’s an essential resource for life and good health, but there’s only a very small part that can be used. This lack of water is due to the freshwater gap on earth, but also to the population pressure, especially in Africa and the Middle East : in the 20th century, the world’s population has tripled, and in the next fifty years, it will increase by another 40 to 50%. Coupled with industrialization and urbanization, it will result in an increased demand : the per capita use will increase, due to those changes in lifestyle, whereas the population is also increasing : The world’s population is growing at a rate of 80 million people each year.

More than one out of six people lack access to safe drinking water. Indeed, even if some people can access to water, this water is contaminated : pollution is becoming a huge factor in destroying the fresh water supply. Some 3900 children die every day from water diseases in 2002, a child dies every 20 seconds from a water-related illness and 3 575 million people die each year from water-related diseases. It’s very important to find a solution to this water crisis, because it claims more lives through diseases than any war claims through guns.

Furthermore, those freshwater availabilities are unequally distributed on the earth surface. Due to this problem, water has become an inequalities and conflicts source. Indeed, over 260 rivers pass through two or more countries. If there are not strong institutions, it can lead to tensions. For example, Egypt threatened to declare war to Ethiopia if this country carries out its project : divert the Blue Nile water for its agriculture.
Africa is already one of the driest continents in the world, and it’s facing water stress and water scarcity.

The concept of Water Stress

We talk about water stress when the water demands exceed water resources. The water stress indicator on this map measures the proportion of water withdrawal with respect to total renewable resources. Water stress causes deterioration of fresh water resources in terms of quantity (aquifer over-exploitation, dry rivers, etc.) and quality (eutrophication, organic matter pollution, saline intrusion, etc.). We consider a country in water stress when the water availabilities, per year and per capita are lower than 1 700 cubic meters and when annual water supplies drop below 1,000 cubic meters per person, the country faces water scarcity. Almost 600 million people are facing water stress or water scarcity, and if the current consumption patterns continue, two out of every three people on Earth will live in water-stressed conditions by the year 2025.

A lot of conflicts due to water begin inside countries, and they oppose intensive farmers and population in water stress. On the one hand, there is a lack of water in a lot of countries, but on the other hand, water withdrawals for irrigation represent 66% of the total withdrawals. Agriculture is one of the activities that use more water. It’s not possible to satisfy farmers as well as poor people living in Africa, for example, and unfortunately, farmers are powerful. That’s why some people don’t have water ; the water that they could consume is used by farmers. For example, 5263 water liters are needed to obtain 1 kg of cotton, and 590 for 1 kg of wheat. They need water to irrigate and produce more and more, to export their productions and become richer. As Gandhi said, “There is a sufficiency in the world for man’s need but not for man’s greed.”

That’s why the water crisis needs solutions, and we think that science could be a solution. And there are a lot of solutions to clean up water, to desalinate water…

We have chosen 3 original and unknown solutions : reverse osmosis, powdered water and fog net :

  • Reverse osmosis

The best-known is reverse osmosis, a process to desalinate water. It’s the opposite of osmosis, a natural movement of solvent molecules through a partially permeable membrane into a region of higher solution concentration, in order to equalize the solute concentrations on both sides. This mechanism is natural, for example, it allows passage of oxygen from lungs to the blood.
Reverse osmosis consists in applying a pressure, thanks to a gas system, superior to osmotic pressure . When we apply this pressure, the flux reverses. Because the membrane is semi permeable, salt, impurities, virus, bacteria… can’t pass through the membrane, and we obtain drinking freshwater. This technique makes it possible to eliminate all molecules largest than one micrometer.
The best-known is reverse osmosis, a process to desalinate water. It’s the opposite of osmosis, a natural movement of solvent molecules through a partially permeable membrane into a region of higher solution concentration, in order to equalize the solute concentrations on both sides. This mechanism is natural, for example, it allows passage of oxygen from lungs to the blood.
Reverse osmosis consists in applying a pressure, thanks to a gas system, superior to osmotic pressure . When we apply this pressure, the flux reverses. Because the membrane is semi permeable, salt, impurities, virus, bacteria… can’t pass through the membrane, and we obtain drinking freshwater. This technique makes it possible to eliminate all molecules largest than one micrometer. This process requires water pre-treatment to eliminate largest impurities that could fill the membrane holes and a mineralization too.

Where can this process be used ?
Firstly, desalinating water is a chemical process that can be used only in countries near to saltwater sources (seas and oceans). Countries which can desalinate water have limited water availabilities, but they have to be rich, for example, Spain, Kuwait, Kazakhstan or Saudi Arabia. The largest factory in the world is in Israel : it produces 108 million cubic meters freshwater per year, about the consumption of a city of 1,4 million inhabitants.

But desalinating has drawbacks : it can’t be used in the majority of countries because of the lack of sea proximity, and it needs a lot of energy that’s why it’s very expensive.

  • Powdered water

Powdered water is an experimental scientific invention. It may be one of the future solutions to avoid wasting water in agriculture, or to transport water.
Powdered water looks like sugar, but water is actually not really powdered, it is formed with silica, and water is enprisoned in hydrophobic silica microcapsules. If we compress this powder, the water gets away from its capsules because the capsules burst.
This process is not very expensive and it can be applied on a large scale but it already needs water. It can enable farmers to do drop by drop in agriculture and it can save cultivations during drought. This use is very interesting : we can sow capsules and seeds at the same time. Later, when the ground is dry, it will become more compact and compress the capsules, thus releasing water.

  • Fog net

The previous two solutions are not to increase water availabilities, contrary to this one : collecting fog water. Indeed, fog is composed of 2 to 5 micrometers droplets, so small that they don’t fall to the ground.
We can collect this water thanks to polypropylene nets. Polypropylene is plastic substance which is recyclable and waterproof. The fog water stream down the nets, then it is collected in drainpipes and stocked in tanks. Net meshes extract 30% of fog wetness, between 17 to 42 water liters per square meter per day. This process was inspired by spider web.
This technique can be applied only in some places, such as coastal mountains. Nets have to be installed perpendicularly to wind. Contrary to desalinate water, water fog is rich in calcium and sodium. It could be used as mineral water.
There are only a few drawbacks : the nets often tear away, and it is better to live in a non polluted place.

As a conclusion, we can say that there is a water crisis all over the world, but there are solutions : to avoid wasting water, as with powdered water, and to increase freshwater availabilities such as reverse osmosis and fog nets, but those solutions are only local. The most important is to find the right solution for each place.