In the guide below, we outline some of the important aspects of water desalination.
We discus what it is, the different types & methods, processes used, examples of where it’s currently used in the world, and more.
What Is Desalination, & How Does It Work?
Desalination is the process of removing salt from water, to produce fresh water.
To be more specific, the desalination process removes salt, and other unwanted minerals, particles and impurities (including pollutants), from different types of water, such as salt water, saline water, and brackish water (which all contain different levels of salt and different concentrations of total dissolved solids)
The twdb.texas.gov resource goes into more detail about the different types of water, and their makeup
Desalination commonly converts sea water into either potable water (drinking water), or non potable water (water that can’t be consumed, but can be used for other uses such as irrigation in agriculture, and different industrial uses)
Large Scale vs Small Scale Desalination
Both large scale and small scale desalination exist.
Large scale desalination produces larger amounts of fresh water for wider society, whereas small scale desalination can be carried out on an individual level with small ‘Reverse Osmosis Membrane’ products, and similar products.
Desalination can also be used on ships and submarines on a small to medium scale
This guide focusses on large scale desalination for society i.e. desalination plants producing larger volumes of water
Coastal Desalination Facilities vs Inland Desalination Facilities
The main difference between these types of desalination facilities is:
– Coastal desalination facilities are located on coastlines and mainly desalinate seawater
– Inland desalination facilities are located inland from coasts, and process brackish water (less salty than seawater) from sources such as aquifers and rivers
wired.com indicates that: ‘[Inland desalination plants are] more efficient than coastal plants …’
Map Showing Locations Of All Inland & Coastal Desalination Plants In The World
wired.com also has a map that shows the location of all the coastal and inland desalination plants in the world, and also indicates the capacity of each plant, as well as the industry/sector that the produced water goes to (i.e. who the client for the produced water is)
Desalination Facilities, Technology, Processes & Methods
There’s two main types of desalination facilities that use different types of technology:
1. Thermal Based Desalination
Generally involves heating water with a high salt content, harvesting the more pure water vapor, and then pumping out the brine by-product.
Thermal based desalination is an older, more traditional technology that used to make up majority of desalination facilities.
2. Membrane Based Desalination
Generally involves pushing water with a high salt content through several filters or ‘membranes’ with pressure, to remove the salt.
Membrane based desalination technology is the technology that is used at a much greater rate in recent times.
These types of desalination facilities/technology outlined above use different processes/methods to convert water with a higher salt content into freshwater:
Thermal Based Desalination
– Distillation
There’s several forms of distillation, however distillation involving boiling water with a higher salt content to get water vapor, and then condensing this water vapor, separating it from salt and other unwanted impurities in the original feedwater.
Multi-stage flash distillation might be one of the more common methods of distillation used worldwide.
Membrane Based Desalination
– Osmosis
The most widely used process or method that uses membrane based technology, is ‘Reverse Osmosis’ (also referred to as ‘RO’)
wired.com notes that ‘RO facilities now produce 69 percent of desalinated water worldwide’, and the reason is that (paraphrased) ‘[This process is cheaper and more efficient, because RO requires less pressure and energy to filter seawater, and produces less brine]’
Having said that, wired.com also notes that ‘[RO is least efficient for highly saline water, and more efficient for less saline water]’
Other Information On These Technologies, Processes & Methods
wikipedia.org lists and explains the different technologies, processes, and methods in their report, such as the other forms of distillation and also osmosis
They also describe other forms of desalination, such as ‘Freeze-thaw Desalination’, and ‘Microbial Desalination’
Large.stanford.edu also mentions a third type of desalination – electrical.
ide-tech.com also has more information about the different technologies in their guide
Waste By Products From Desalination – Brine
‘Brine’ is the main waste by product of desalination.
Brine is a form of highly concentrated saline water
Most of the world’s brine may currently come from a small number of countries currently running older, more inefficient desalination plants
Where Most Of The World’s Brine Comes From
According to wired.com: ‘… only four nations—Saudi Arabia, the United Arab Emirates, Kuwait, and Qatar—produce 55 percent of global desal brine [and, this brine mostly comes from coastal plants using …] older, inefficient thermal plants [instead of RO plants that the rest of the world is using]’
Examples Of Desalination Around The World
Desalination is widely used around the world, with many plants currently being in the Middle East
Some cities already receive a large % of their water supply from desalination
How Many Desalination Plants Are Currently In Operation?
wikipedia.org indicates there’s 21,000 desalination plants currently in operation around the world
There are about 18,426 desalination facilities located in 150 countries worldwide with a total capacity of about 22.9 billion US gallons, based on 2017 numbers (twdb.texas.gov)
Where Are Most Desalination Plants Currently Located In The World?
In 2015, 53% of desalination plants were located in the Middle East, and 17% in North America (brandongaille.com)
Examples Of Cities Using Desalination For Larger %’s Of Their Water Supply
wikipedia.org mentions that the largest desalination plant in the world is currently located in Saudi Arabia, and the UAE, Saudi Arabia and Israel have some of the largest plants overall (in terms of their capacity)
How Much Does Desalination Cost?
The cost of desalination can vary between different regions within different countries, and over time, improvements or increased development with desalination may lead to lower costs.
However, right now, various reports indicate that seawater desalination might be the most costly water source to produce, with brackish desalination being the fourth (behind water reuse).
One report by mercurynews.com indicates that (paraphrased from a graphic/table), the price to produce water from different water sources is as follows:
Seawater Desalination – $2200 to $4300
Indirect Potable Reuse – $1600 to $2700
Nonpotable Reuse – $1500 to $2100
Brackish Desalination – $950 to $1800
Stormwater Capture – $570 to $1600
Surface Water – $386 to $1884
Groundwater – $90 to $960
These costs may be reflected in the water bills that consumers pay.
Additionally, wikipedia.org mentions that (paraphrased), transport costs (of transporting desalinated water further from where it’s produced, and having to pump it longer distances) can significantly add to costs.
wikipedia.org also has a table that shows how much the different forms of desalination cost, with Reverse Osmosis appearing cheapest per liter
They also show the cost of supply of seawater desalination in different countries, with the US being one of the most expensive countries on a USD per cubic metre, per person, per day basis
Desalination Machines, Units & Systems
Some companies manufacture desalination machines, units and systems for use in ships and submarines, and for other medium size desalination production.
Portable Desalination Filters, Hand Pumps, & Kits
Small and/or portable desalination filters, hand pumps, kits and similar products are also available for personal/individual use
Potential Pros & Cons Of Water Desalination
Read more about the potential pros and cons of desalination in this guide.
Desalination vs Water Recycling Comparison
We’ve put together a separate guide outlining the differences between, and providing a comparison of desalination and water recycling.
Sources
1. http://large.stanford.edu/courses/2011/ph240/parise2/
2. http://www.twdb.texas.gov/innovativewater/desal/faq.asp#title-18
3. https://www.ide-tech.com/en/solutions/desalination/what-is-desalination/?data=item_1
4. https://brandongaille.com/22-top-pros-and-cons-of-desalination/
5. https://www.wired.com/story/desalination-is-booming-but-what-about-all-that-toxic-brine/
6. https://en.wikipedia.org/wiki/Desalination
7. https://www.mercurynews.com/2019/09/27/100-million-desalination-project-to-be-led-by-lawrence-berkeley-national-lab
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