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How does a desalination plant work?
DW (English)
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9 months ago
Two different processes are used to obtain freshwater from saltwater – distillation and reverse osmosis. It takes around 100 liters of seawater to produce 45 liters of drinking water. Our viewer question this time comes from Richard Z. in Colombia.
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00:00
How does a desalination plant work?
00:05
There are various ways of turning seawater into fresh water.
00:09
Two methods are commonly used on an industrial scale.
00:12
The first is distillation.
00:15
Under vacuum pressure, seawater is heated to 115 degrees Celsius.
00:20
As the water vaporizes, it leaves the salt behind.
00:24
The vapor flows through a cooled pipe, turning to fresh water.
00:28
But of the more than 20,000 desalination plants worldwide,
00:32
only about 20% use distillation.
00:35
The second method is reverse osmosis.
00:38
In this method, water is forced under pressure through a membrane.
00:42
The semipermeable membrane lets water molecules pass through
00:46
while blocking substances like salt and minerals.
00:49
The water on the one side is salt-free, while the other is very salty.
00:54
Even though the cost of desalination has dropped, it's still expensive.
00:58
Obtaining drinking water from 1,000 litres of river water costs just 5 Eurocents,
01:05
while just 1 litre of seawater costs 50 Eurocents.
01:10
In addition, both methods require a great deal of energy,
01:14
much of which still comes from fossil fuels.
01:18
But some smaller desalination plants can now meet their energy needs
01:22
with renewable sources.
01:26
Obtaining 45 litres of pure water through desalination
01:30
requires 100 litres of seawater.
01:33
What's left is called brine.
01:35
It's extremely salty, low in oxygen and often contaminated with chemicals.
01:40
Before it's pumped back into the ocean,
01:43
sometimes some of the salt, sodium chloride, is filtered out.
01:47
But the brine also contains magnesium and potassium,
01:51
which have commercial uses.
01:54
However, extracting these minerals is costly and energy-intensive.
02:00
Researchers are exploring nanofilters and other methods
02:04
to see how valuable minerals and elements can be recovered from brine more efficiently.
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