Desalination: ecological cost remains neglected, to the benefit of access to water

From 1872, the year in which Chile developed the world’s first seawater desalination plant (20,000 m³ per day), to the present day, the use of this non-conventional water resource has evolved considerably, to such an extent that this practice has become unavoidable for certain countries, notably Libya, where it appears to be a transitional solution. In this North African country, rainfall is virtually non-existent. This situation has reduced the quantities of water that run off and seep into dams, rivers, lakes, etc., forcing the government in Tripoli to withdraw eight times as much renewable water from its territory every year.

Like Libya, many countries in Africa have adopted this practice, mainly those in the North Africa sub-region (Morocco, Egypt, Tunisia, Algeria). Next come the Southern and Eastern Africa sub-regions, where desalination is also improving water supplies, particularly for households and farmers. Beyond the African continent, this solution is very widespread in the West Indies (island of Malta, etc.) and in the Arab countries, where the largest desalination plant in the world is located. This is the Ras Al Khair plant in Saudi Arabia (1,036,000 m³ per day).

“Desalination is helping to mitigate these bad trends and could even succeed in offsetting them. In reality, there are no limits, because the sea has a phenomenal quantity of water”, explains Francois Guerber, head of the International Observatory of Non-conventional Waters and Associated Renewable Energies project at the Mediterranean Water Institute (IME).

So, if desalination seems to be making all the difference, why is it still not unanimously supported in 2024?

Marine life is threatened

Because for many environmentalists and players in the water sector, seawater desalination remains an ecological disaster, despite the water benefits it is said to bring. “I think we’re going to lose out on desalination in the long term. We’re paying a lot of money to treat seawater, and from an environmental point of view, we’re releasing highly concentrated brine into the ocean, which is killing biodiversity. Let’s leave our fish alone”, laments Malek Semar, founder of the “No Water No Us” association, which raises awareness and takes action on water issues in Africa and elsewhere.

Francois Guerber, from the IME, also points out this colossal disadvantage, before specifying the quantities of brine returned to the marine environment. “We’re going to pump water into the sea, we’re going to transform some of it into fresh water and then we’re going to pump back just as much, or even a little more (twice as much) water that will be concentrated in salt, i.e. 70 mg per litre of seawater instead of 36 mg per litre (the amount of salt contained in undesalinated water), which we’re going to pump back into the sea, increasing the temperature of the water. And it’s the aquatic fauna that will be affected”. 

If the practice of desalinating water dates back more than 150 years, or 60 years for commercial desalination which began around 1965 with a global capacity of around 8,000 m³ per day in 1970 to reach around 86.6 million m³ per day at the end of 2015 and a little more today, we can well imagine the significant flow of brine that has been discharged over the years into our marine spaces. “The discharge of brine into the sea results in the formation of a stratified system of increasingly salty layers moving towards the seabed, which reduces the mixing between seabed water and surface water. In some cases, and depending on local marine currents, 40% of the surrounding area is covered in salt”, stated the United Nations Environment Programme (UNEP) in a report published in 2003.

In both these cases, we are talking about anoxia (absence of oxygen) on the seabed, and a reduction in light insofar as the presence of hypersaline water causes the formation of a fog that makes it difficult for light to pass through, thus affecting the photosynthesis of marine plant species. It should be noted that seawater desalination accounts for around 60% of desalination efforts worldwide, and more than 80% around the Mediterranean.

The damage will be less severe when it comes to desalinating brackish water, which environmentalists claim contains less salt. On the African continent, desalination of brackish water is common in Eastern and Southern Africa.

Energy-intensive processes

“I’m not against desalination. H2O molecules (the chemical formula for water) have been recycling naturally for ages, and they will continue to do so with desalination. But this should only happen after we have solved our problems on earth, namely the treatment and reuse of all our urban, agricultural and industrial wastewater, a process that requires less energy than desalination”, Malek Semar, founder of the “No Water No Us” association, which raises awareness and takes action for water in Africa and elsewhere, points out.

Francois Guerber does not entirely share the view that water shortages can be solved using treated wastewater alone. “The volumes of treated wastewater are far below what is needed to meet the demand for irrigation in this particular case. This is because the volumes of effluent are smaller than those of seawater. Desalination is therefore the best solution for reducing the global deterioration in water supply caused by climate change and demographic and economic growth”, he explains.

The manager of the International Observatory of Non-conventional Waters and Associated Renewable Energies project at the Institut Méditerranéen de l’Eau (IME) nevertheless adds that despite the reverse osmosis process, which is a widespread and very mature technology with much lower energy consumption than in the past, we still manage to consume 2.5 kWh per cubic metre, compared with 4 kWh for a plant that does not use this technology. “Even if electricity consumption is lower with reverse osmosis, 2.5 kWh is still a lot. It’s about the same amount of energy used to pump the water up to a height of 1,000 m”.

Can the disadvantages of desalination be overcome?

On the energy front, Francois Guerber recommends reducing excess energy consumption by favouring renewable energies over fossil fuels. While this is already being done by a number of companies and start-ups, such as the German start-up Boreal Light, which supplies several African countries with its containerised solutions, or GivePower, an American organisation specialising in clean energy, whose latest project in Africa was inaugurated in 2023 in Mombasa, Kenya, this should be a sine qua non condition for desalinating seawater, according to the researcher. “Because if we had to use fossil fuels alone, I would totally agree with the environmentalists, given the phenomenal amount of greenhouse gas (GHG) emissions that would result”.

As for the disposal of brine, the first solution might be to dispose of the water not in a shallow area, but where there is a lot of current, and to re-mix the salt correctly with the same concentration as in the sea.“That’s called diffusing discharge. Of course it’s more expensive than not doing it, but it’s perfectly feasible”, suggests François Guerber.

The second solution would be to extract minerals from the brine that is discharged into the sea, in particular lithium, in order to sell it to the automotive industries that manufacture batteries. According to François Guerber, the only problem with this approach is that it could lead to numerous problems, including soil pollution and the plundering of water reserves.

“In the latter case, we can also simply recover the salt. We concentrate the salt in seawater by evaporating the water until we have crystallised salt”, explains François Guerber, who took these proposals to Bali in Indonesia, where the 10th World Water Forum was held from 18 to 24 May. This will be part of an exchange of international actions, where countries with less experience of desalination can learn from those with good techniques and who are making efforts to make the desalination process more sustainable. This is the case of the Americans, the Saudis, the Spanish, the Israelis and the French.

The possibility of strengthening the regulatory frameworks for water desalination was also raised, in order to make this practice more effective in meeting the Sustainable Development Goals (SDGs). In this respect, desalination is currently compromising the health of marine ecosystems (SDGs14).