Over one-third of the world's population, already struggling to keep up with the demand for fresh water, could quench their thirst if salty seawater could be filtered by a cheap process called reverse osmosis, according to a new study.
The Yale University study has argued that seawater desalination should play an important role in helping combat worldwide fresh water shortages and provides insight into how desalination technology can be made more affordable and energy efficient.
Reverse osmosis - forcing seawater through a membrane that filters out the salt - is the leading method for seawater desalination in the world today. For years, scientists have focused on increasing the membrane's water flux using novel materials, such as carbon nanotubes, to reduce the amount of energy required to push water through it.
Now, Menachem Elimelech, a professor of chemical and environmental engineering at Yale and lead author of the study, and William Phillip, now at the University of Notre Dame, demonstrated that reverse osmosis requires a minimum amount of energy that cannot be overcome, and that current technology is already starting to approach that limit.
Instead of higher water flux membranes, Elimelech and Phillip suggested that the real gains in efficiency could be made during the pre- and post-treatment stages of desalination.
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 the water to clean it and help coagulate this matter for easier removal during a pre-treatment stage. But if a membrane didn't build up organic matter on its surface, most if not all pre-treatment could be avoided, according to the scientist's findings.
In addition, Elimelech and Phillip calculate that a membrane capable of filtering out boron and chloride would result in substantial energy and cost savings.
Elimelech cautions that desalination should only be considered a last resort in the effort to provide fresh water to the world's population and suggested that long-term research is needed to determine the impact of seawater desalination on the aquatic environment, but believes that desalination has a major role to play now and in the future.
"All of this will require new materials and new chemistry, but we believe this is where we should focus our efforts going forward," said Elimelech.
The study has been published in the journal Science.