Desalination of seawater

[lpetrich]

The decades-long quest to end drought (and feed millions) by taking the salt out of seawater | WIRED UK

“The world isn’t short of water, it’s just in the wrong place, and too salty," says Charlie Paton – so he's spent the past 24 years building the technology to prove it

...
Paton is the founder of Seawater Greenhouse, a company that transforms two abundant resources – sunshine and seawater – into freshwater for growing crops in arid, coastal regions such as Africa’s horn. The drought-stricken landscape that cloaks this region doesn’t exactly inspire visions of lush agriculture – but then, Paton sees things differently: “The world isn’t short of water, it’s just in the wrong place, and too salty,” he says.

His latest project in Somaliland (an autonomous but internationally unrecognised republic in Somalia) takes that bullish optimism to the extreme. On a 25-hectare plot of desert land close to the coastline, he’s building the region’s first sustainable, drought-resistant greenhouse. Using solar power to pump in seawater from the coastline and desalinate it on site, Paton is generating freshwater to irrigate plants, and water vapour to cool and humidify the greenhouse interior. In January – less than a year after its launch – this improbable desert oasis produced its first harvest of lettuce, cucumbers and tomatoes. “The idea is so simple that it’s rather insulting,” Paton says. “People say, ‘If that’s going to work then somebody would have done it before.’”

Seawater Greenhouse

Working with clients and partners around the world, we design greenhouse solutions for hot and dry coastal regions, often where agriculture would otherwise be impossible. Using modeling software to simulate the growing environment, we can optimize a design to maximize the cooling and humidifying effects of our technology. We then custom-design the specific greenhouse to fit the economic and climate conditions of a particular region. Our latest project, where we are piloting an all-new design, is in Somaliland.

They claim:

300-750 tons/ha* Achievable yield, depending on greenhouse design and crop *Using tomato as a reference
50-75% Reduction in capital costs versus traditional heated greenhouses
10-40% Reduction in operating cost versus traditional heated greenhouses

With projects in Tenerife, Abu Dhabi, Oman, Australia, and Somaliland.

 Desalination is a gradually growing technology, with the promise of relieving shortages of fresh water. There are two main ways of doing it: distillation and reverse osmosis. Distillation is a rather obvious method, even though it is rather energy-intensive. Even if one helps it along by pumping out much of the air where the seawater is being boiled, to lower its boiling point and make less heating needed. Reverse osmosis has become common, though it is not much less energy-intensive. It works by squeezing the water part of seawater through a semipermeable membrane.

Energy needed, in kWh per m^3:

• Distillation: 6.5 - 25.2
• Reverse osmosis: 3 - 5.5
• RO thermodynamic limit: 1.5 (source: Energetic Demands of Water Desalination by Reverse Osmosis)

While long-distance water transport can approach 3 kWh/m^3, local water supplies typically need around 0.2 kWh/m^3. That's why dealination has not been very common.

But as renewable-energy generation advances, we may see more desalination, because it can be a good sink for energy-production peaks like midday for solar panels.

Desalination: Drink a cup of seawater? - US Geological Survey

• It is estimated that some 30% of the world's irrigated areas suffer from salinity problems and remediation is seen to be very costly.
• In 2002 there were about 12,500 desalination plants around the world in 120 countries. They produce some 14 million cubic meters/day of freshwater, which is less than 1% of total world consumption.
• The most important users of desalinated water are in the Middle East, (mainly Saudi Arabia, Kuwait, the United Arab Emirates, Qatar and Bahrain), which uses about 70% of worldwide capacity; and in North Africa (mainly Libya and Algeria), which uses about 6% of worldwide capacity.
• Among industrialized countries, the United States is one of the most important users of desalinated water, especially in California and parts of Florida. The cost of desalination has kept desalination from being used more often.

 

[Cycad]

If graphene can be produced cheaply it might make RO obsolete.

It might even bring us closer to creation of floating cities.

 

[lpetrich]

Link with original title: Graphene-based sieve turns seawater into drinking water - BBC News -- it uses graphene for reverse osmosis.

Desalination: is this as good as it gets? | Ars Technica

The total process of desalination turns out to require three to four times the theoretical minimal energy use, since the salt water must be pumped and pretreated, the membranes maintained, and the resulting brine handled afterwards. Some of these things might be amenable to further improvements, and there has been work put into developing membranes that don't clog up as easily or better pre-filtering of biological materials.

 

[Underseer]

This is perhaps some of the most important research going on today.

 

[Loren Pechtel]

This is perhaps some of the most important research going on today.

Isn't the main problem power and not the membrane? (On the other hand, that makes it basically ideal for use with solar power--you run the pumps when you have enough power. Use them to pump water to high tank and use it's pressure to run the system and you can turn them off in the blink of an eye if you need the power for the grid.)

 

[steve_bank]

https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in_Saudi_Arabia
https://www.reuters.com/article/us-...-desalination-plants-on-red-sea-idUSKBN1FA0BG

Saudi Arabia has the biggest program inn the world. I read they are consdering towing icebergs.

As with all else, it comes down to energy.