Desalination could be made cheaper, says team

Desalination of seawater could be the best way to solve the world’s water shortage, say Yale researchers, who have come up with ways to improve its efficiency.

Over a third of the world’s people live in areas that are short of fresh water – and by 2025, that number is expected to nearly double. The team says desalination could be the answer.

“The globe’s oceans are a virtually inexhaustible source of water, but the process of removing its salt is expensive and energy intensive,” says professor of chemical and environmental engineering Menachem Elimelech.

Desalination efforts have focused on reverse osmosis – forcing seawater through a membrane that filters out the salt – and trying to reduce the amount of energy required.

But Elimelech and William Phillip, now at the University of Notre Dame, now say they can show that there’s a certain minimum amount of energy required for reverse osmosis, and that current technology is already starting to approach that limit.

Instead, Elimelech and Phillip suggest that the greatestefficiency gains are to be made during the pre- and post-treatment stages ofdesalination.

Seawater contains naturally occurring organic and particulate matter that must be filtered out before it passes through the membrane that removes the salt. Chemical agents are added to clean the water and and make the matter coagulate so that it’s easier to remove.

But if a membrane didn’t build up organic matter on its surface, most if not all pre-treatment could be avoided, says the team.

They also calculate that a membrane that could filter out boron and chloride would bring substantial energy and cost savings.

Instead of removing them during a separate post-treatment stage, the scientists believe a membrane could be developed that would filter them at the same time as the salt is removed, and more efficiently than can be done now.

“All of this will require new materials and new chemistry, but we believe this is where we should focus our efforts going forward,” saysElimelech.

“The problem of water shortage is only going to get worse, and we need to be ready to meet the challenge with improved, sustainable technology.”