For millennia, humans have sought to make drinkable. Ancient mariners tried distillation by boiling the oceans in which they sailed, and in more recent times, engineers have experimented .
As the , populations surge and , there is a growing need to make the sea drinkable. Desalination technology is spreading fastest in the Middle East, North Africa and parts of Asia, where there is plenty of ocean but
In 2023, there were an estimated 16,000 plants in operation globally, capable of making 56 billion liters of desalinated water a day — around 7 liters for every person on the planet.
But creating drinking water from the sea is not without environmental impacts. These depend on how plants process seawater, whether they run on fossil fuels or renewable energy and where they are built.
Desalination’s salty problem
The major obstacle to using the sea to meet human water needs — which the UN puts at between 50 and 100 liters per person per day — is that it contains too much salt to drink, and actually causes dehydration.
Reverse osmosis, today’s dominant desalination method, uses high-pressure membranes to filter out the salt, leaving behind drinkable water. But every liter produced this way generates an almost equal volume of brine.
This highly salty byproduct is often laced with chemicals like chlorine as well as antiscalants used to prevent salt buildup on equipment.
The easiest and cheapest way to get rid of this brine is to send it back into the sea. But once discharged, it tends to sink, forming dense layers on the ocean floor. These layers deplete oxygen and particularly creatures like mollusks, sponges and seagrasses that provide food and shelter for other species.
Brine also often contains heavy metals from corroding pipes and has been found to harm fish and broader marine ecosystem health.
But if dispersed properly, brine isn’t necessarily harmful, according to Sergio Salinas Rodriguez, an associate professor at IHE Delft Institute for Water Education in the Netherlands.
“Desalination plants add salt-based chemicals like iron chloride or aluminum sulfate to remove dirt, and antiscalants to prevent salt buildup,” he told DW. “But their volume is minuscule compared to the vastness of the ocean.”
Are there ways to lessen the impact of brine?
One way to soften the impact of discharged brine is to dilute it, as happens at the massive Carlsbad Desalination Plant in drought-prone California. The facility produces 50 million gallons (189.27 million liters) of water a day for the San Diego region.
Until the end of 2018, Carlsbad mixed the salty substance with cooling water from a neighboring power station before releasing it into the Pacific Ocean. Since the power plant shuttered, the desalination facility has instead been drawing extra seawater to thin the brine. It uses what it describes as “fish-friendly” pumps to minimize injury to marine creatures.
Once discharged, ocean currents, wave action and the unique geography of the Agua Hedionda Lagoon, where Carlsbad is located, help disperse the salty plume.
Four years of monitoring between 2019 and 2023 found waters off Carlsbad’s coast “remain healthy and minimally impacted,” according to a study commissioned by the company that runs the plant.
Yet 2019 research by scientists at the University of California Santa Cruz found that salinity in brine discharge zones and further ashore sometimes exceeded permitted levels. They said stronger dilution could help.
But such strategies can’t be replicated everywhere. The Persian Gulf, for instance, is shallow, already very salty, and doesn’t have the same natural currents to disperse brine. Which is why knowledge of the local seascape is important when building a desalination plant.
“That needs to be a study of the currents, natural flow, and potential impact,” said Rodriguez.
Mining brine for valuable minerals
Others are looking to brine not as waste, but as a resource.
In Tenerife, Spain, an EU-funded project called Sea4Value is mining desalination brine for critical raw materials. The researchers aim to extract 10 minerals, including vital for batteries and manufacturing. At the same time, they also want to produce more drinking water and less brine waste.
“Our idea was to go from the 50% brine that’s usually produced to reduce it to around 20%,” said Sandra Casas Garriga, a researcher involved in the project. “So, from one cubic meter of seawater, we could obtain 800 liters of freshwater and 200 liters of brine.”
Early trials carried out in a mobile lab unit successfully tested different techniques for recovering critical minerals from the byproduct. “We try to be as green as possible by reducing the impact of the process of recovery,” said Garriga, in reference to the fresh water and critical minerals drawn from the sea.
Other companies, including in the US, are also running pilot projects to test ways of extracting minerals like magnesium from brine.
Choosing the right location for desalination
Some of desalination’s other environmental impacts could be lessened by choosing the right plant location, say experts.
Kotb Mohamed, a postdoctoral fellow at the Interdisciplinary Research Center for Sustainable Energy Systems in Saudi Arabia, created a tool that identifies the best locations for seawater reverse osmosis plants powered by solar and wind.
The model was first tested on Egypt’s Red Sea Coast and can be applied to arid coastal regions in North Africa, the Gulf, South Asia and parts of Europe, he said. Most desalination plants currently run on the fossil fuels that emit planet-heating greenhouse gases.
“There are three major environmental benefits of the model, which are and , minimized land degradation or erosion and efficient use of local resources.”
He added that plants built near population centers with existing infrastructure could avoid long water pipelines, thereby saving energy and land, though this may not be feasible in less developed areas.
“When done properly, and all cares are taken, is environmentally defensible,” said Rodriguez from the Delft Institute. “But it needs to take the proper measures […] from the design of the plant, finding a location in the sea that is proper for abstracting the water and also for discharging.”
Edited by: Jennifer Collins
The post Desalination doesn’t have to be bad for the environment appeared first on Deutsche Welle.
