Better desalination technology would help solve world’s water shortage

Over one-third of the world's population already lives in areas struggling to keep up with the demand for fresh water. By 2025, that number will nearly double. Some countries have met the challenge by tapping into natural sources of fresh water, but as many examples - such as the much-depleted Jordan River - have demonstrated, many of these practices are far from sustainable.

Some countries have met the challenge by tapping into natural sources of fresh water.

A new Yale University study argues that seawater desalination should play an important role in helping combat worldwide fresh water shortages once conservation, reuse and other methods have been exhausted. The study also provides insights into how desalination technology can be made more affordable and energy efficient.

''The globe's oceans are a virtually inexhaustible source of water, but the process of removing its salt is expensive and energy intensive,'' said Menachem Elimelech, a professor of chemical and environmental engineering at Yale and lead author of the study, which appears in the August 5 issue of the journal Science.

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.

In the new study, Elimelech and William Phillip, now at the University of Notre Dame, demonstrate 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 suggest that the real gains in efficiency can 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.