UN Research Warns of Toxic Side Effects of Desalination
The fast-rising number of desalination plants worldwide—now almost 16,000, with capacity concentrated in the Middle East and North Africa—quench a growing thirst for freshwater but create a salty dilemma as well: how to deal with all the chemical-laden leftover brine.
In a UN-backed paper, experts estimate the freshwater output capacity of desalination plants at 95 million cubic meters per day—comparable to 40% of the high season flow over Niagara Falls.
For every liter of freshwater output, however, desalination plants produce on average 1.5 liters of brine (though values vary dramatically, depending on the feedwater salinity, the desalination technology used and local conditions). Globally, plants now discharge 142 million cubic meters of hypersaline brine every day (a 50% increase on previous assessments).
That’s enough in a year (51.8 billion cubic meters) to cover Florida under 30.5 cm of brine.
The authors, from UN University’s Canadian-based Institute for Water, Environment and Health, the Netherlands Wageningen University and the Gwangju Institute of Science and Technology in Korea, analyzed a newly-updated dataset—the most complete ever compiled—to revise outdated statistics on desalination plants.
They call for improved brine management strategies to meet a fast-growing challenge, noting predictions of a dramatic rise in the number of desalination plants, and hence the volume of brine produced, worldwide.
The paper found that 55% of global brine is produced in just four countries: Saudi Arabia (22%), UAE (20.2%), Kuwait (6.6%) and Qatar (5.8%). Middle Eastern plants, which largely operate using seawater and thermal desalination technologies, typically produce four times as much brine per cubic meter of clean water as plants where river water membrane processes dominate, such as in the U.S.
The paper says brine disposal methods are largely dictated by geography but traditionally include direct discharge into oceans, surface water or sewers, deep well injection and brine evaporation ponds. Desalination plants near the ocean (almost 80% of brine is produced within 10 km of a coastline) most often discharge untreated waste brine directly back into the marine environment.
The authors of the recent paper cite major risks to ocean life and marine ecosystems posed by brine greatly raising the salinity of the receiving seawater, and by polluting the oceans with toxic chemicals used as anti-scalants and anti-foulants in the desalination process (copper and chlorine are of major concern).
“Brine underflows deplete dissolved oxygen in the receiving waters,” says lead author Edward Jones, who worked at UNU-INWEH and is now at Wageningen University, The Netherlands. “High salinity and reduced dissolved oxygen levels can have profound impacts on benthic organisms, which can translate into ecological effects observable throughout the food chain.”
Meanwhile, the paper highlights economic opportunities to use brine in aquaculture, to irrigate salt-tolerant species, to generate electricity and by recovering the salt and metals contained in brine, including magnesium, gypsum, sodium chloride, calcium, potassium, chlorine, bromine and lithium.
With better technology, a large number of metals and salts in desalination plant effluent could be mined. These include sodium, magnesium, calcium, potassium, bromine, boron, strontium, lithium, rubidium and uranium, all used by industries, in products and in agriculture. The needed technologies are immature, however; recovery of these resources is economically uncompetitive today.
According to Dr. Vladimir Smakhtin, a co-author of the paper and the director of UNU-INWEH, whose institute is actively pursuing research related to a variety of unconventional water sources, “There is an urgent need to make desalination technologies more affordable and extend them to low-income and lower-middle income countries. At the same time, though, we have to address potentially severe downsides of desalination—the harm of brine and chemical pollution to the marine environment and human health.”