Desalination brine gets dumped back into ocean. This is a problem

Carlsbad desalination plant. San Diego

Desalination produces drinking water from sea water and is widely used in the Middle East and North Africa. However, desal produces enormous amounts of brine, which is dumped back into the water supply. Desalination brine is terrible for marine life, and is made worse by chemicals added to the desal process. Also, desalination requires enormous amounts of electricity. Thus, the process is messy and expensive.

The Carlsbad desal plant in San Diego is a good example of the complexities. It cost $1 billion to build and produces 7% of water for the area. An acre foot of water costs considerably more than reclaiming water. (However, this is still less expensive than importing water from outside San Diego.) Carlsbad is a highly advanced plant. Yet, it still pumps desalination brine that is 20% more saline than seawater back into the ocean.

Desal plants in MENA tend to be old-school thermal plants that aren’t particularly efficient. They produce enormous amounts of brine. In addition, they run on natural gas. The whole thing is an environmental mess. Replacing these plants would cost many billions, so isn’t going to happen any time soon. Modern reverse osmosis plants are more efficient, use less energy and produce less waste. However, disposing of the brine remains an issue.

On the intake side, Burt says that small organisms such as fish larvae and coral can get sucked into a plant. But the greater risk comes at the other end of the process, when the brine is put back into the ocean (where the majority of desalination is done).

“Brine will be substantially higher in salinity than normal oceanic water,” he said. “The brine discharge is also warm.” Those conditions, he says, can make it more difficult for marine life in the immediate vicinity of the discharge to survive or thrive.

What Burt is more concerned about, however, are the chemicals that are often in the brine. Qadir’s study points to copper and chlorine as particularly troublesome compounds. These chemicals are added to the seawater at various stages in the desalination process, to control bacterial growth or reduce corrosion, and many end up in the wastewater.