To Win, Remove Salt from Seawater Cheaply

How is it that we have deadly water shortages on a world covered mostly by water? Unfortunately, sea water kills most crops and we can’t drink it due to the high salt content. Effective large scale salt removal from of sea water could therefore save millions of lives. With climate change happening we need more than the 15,906 operational desalination plants we currently have. Did you know we had that many?

Desalinating sea water is much more expensive than getting fresh water from rivers or groundwater, water recycling and water conservation, but for many places on earth, desalinating is their only option. (source)

Because only 2.5 % of water on earth is fresh water and since most of that is inaccessible, trapped in snow fields and icebergs, only 0.007 percent of the planet’s water is available to fuel and feed its 6.8 billion people. (Source)

Worldwide, some 700 million people don’t have access to enough clean water. In 10 years the number is expected to explode to 1.8 billion. In many places, squeezing fresh water from the ocean might be the only viable way to increase the supply.

Cleaning up ocean water easier said than done, but mega scale desalination plants have been operating for years. In one example:

[A company called] Sorek will profitably sell water to the Israeli water authority for 58 U.S. cents per cubic meter (1,000 liters, or about what one person in Israel uses per week), which is a lower price than today’s conventional desalination plants can manage. What’s more, its energy consumption is among the lowest in the world for large-scale desalination plants.

Via TechReview

The Sorek plant is currently ranked number 4 in the world, producing fresh water at a rate of 624,000 m3/day.

A cost of 58 cents per cubic meter is quite good, but can we do even better?

The average price of water in the United States is about $1.50 for 1,000 gallons. At that price, a gallon of water costs less than one penny. (Source)

There are 3.79 cubic meters in 1,000 gallons, so $2.20 is the cost to make 1,000 gallons of fresh water from sea water with the Sorek reverse osmosis process. A sea water source can match the average price of water in the USA if made desalination can be made 70 cents cheaper per 1,000 gallons.

How might this be done? Graphene filters may be part of the answer.

A UK-based team of researchers has created a graphene-based sieve capable of removing salt from seawater. …  The promising graphene oxide sieve could be highly efficient at filtering salts, and will now be tested against existing desalination membranes.

It has previously been difficult to manufacture graphene-based barriers on an industrial scale. Reporting their results in the journal Nature Nanotechnology, scientists from the University of Manchester, led by Dr Rahul Nair, shows how they solved some of the challenges by using a chemical derivative called graphene oxide.

…”To make it permeable, you need to drill small holes in the membrane. But if the hole size is larger than one nanometre, the salts go through that hole. You have to make a membrane with a very uniform less-than-one-nanometre hole size to make it useful for desalination. It is a really challenging job.”

Graphene oxide membranes have already proven their worth in sieving out small nanoparticles, organic molecules and even large salts. But until now, they couldn’t be used to filter out common salts, which require even smaller sieves. …

When common salts are dissolved in water, they always form a “shell” of water molecules around the salt molecules.

This allows the tiny capillaries of the graphene-oxide membranes to block the salt from flowing through along with the water.

“Water molecules can go through individually, but sodium chloride cannot. It always needs the help of the water molecules. The size of the shell of water around the salt is larger than the channel size, so it cannot go through,” said Dr Nair. …

By 2025 the UN expects that 14% of the world’s population will encounter water scarcity. As the effects of climate change continue to reduce urban water supplies, wealthy modern countries are also investing in desalination technologies.
Current desalination plants around the world use polymer-based membranes. …

read more BBC

In 2019 we have 15,906 operational desalination plants on earth generating about 95.37 million cubic meters of useable water per day. (Source). That’s 25.19 billon US liquid gallons of water per day.

Number one in terms of production is the Ras Al Khair Power and Desalination Plant in Saudi Arabia, producing fresh water at a rate of 1,036,000 m3/day. (Source) That’s 273,682,246 US liquid gallons of water per day.

The Ras Al Khair plant – the largest combined power and desalination facility in the world – includes multi stage flash and seawater reverse osmosis desalination and deploys the largest membrane plant in the Gilf of Oman. It also uses dissolved air flotation pre- treatment in converting more than 1 billion litres of seawater into potable water each day.


If we consider need at 100 litres of water per person per day, the world wide demand for 8 billion people is roughly 800 billion liters or 211 billion gallons of water per day. Our 15,906 desalination plants create about 25 billion of that daily need now, about 11.8%.

The bottom line: We need breakthroughs to increase fresh water production enough to sustain projected growth and to buffer larger swings in water availability due to climate change. The cheapest potable water producers will win big time.

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