The ocean is a virtually limitless source of water, if we can get the salt out.
Currently, the process is almost prohibitively expensive, but if costs can come down, the technology could quench the thirst of billions.Israel announced this month it would build a half-billion-dollar desalination plant, joining its four other plants, to provide three-quarters of the country’s fresh drinking water by 2013. Where Israel goes, much of the drought-stricken world will probably follow. With 1.8 billion people expected to live in areas with extreme water scarcity by 2025, desalination–removing salt from ocean water or others saline water–is being viewed as a newly viable solution to the world’s water woes.
There may not be much choice: The world simply doesn’t have much more fresh water. Most of the accessible clean rivers and lakes have been tapped, primarily for agriculture, while the levels of underground reservoirs that filled over thousands or millions of years are dropping at alarming rates. After conservation and reuse, this leaves only a handful of technologies to provide enough water for people and industries in the most arid areas.
But reverse osmosis (RO), the leading desalination method worldwide, is reaching the limits of its efficiency, according to a new paper by Yale University researchers in the journal Science. RO forces seawater through a membrane to remove salt. While research has focused on new materials for this membrane, such as carbon nanotubes, to make the process more efficient, those gains are minuscule in the face of how much water we’re going to need to desalinate, says Menachem Elimelech, lead author of the paper.
“The globe’s oceans are a virtually inexhaustible source of water, but the process of removing its salt is expensive and energy intensive,” Elimelech, a professor of chemical and environmental engineering at Yale, said in a statement.
Instead of small improvements to efficiency, Elimelech’s team wants to revolutionize the entire process, by making a series of membranes for the pre- and post-treatment stages of desalination. Today, we use chemicals that don’t remove enough organic matter from the water, which clog the main reverse osmosis filters, requiring expensive cleaning. If the water was cleaner by the time it got there, the costs of removing the salt could plummet. And then desalination plants–currently considered almost too expensive to be worthwhile–could begin to sprout in less-developed water-poor countries.
But we’ll need to see some of these breakthroughs first. “All of this will require new materials and new chemistry, but we believe [this new process] is where we should focus our efforts going forward,” Elimelech said. “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.”