There are a number of ways to achieve desalination and they don’t all require heavy equipment or tricked-out laboratories; you can do it crudely by boiling water on your stove top. But it wasn’t until the 1960s that an Israeli scientist by the name of Sidney Loeb developed a new method of desalination that launched the process into the modern era.
Working at UCLA, Professor Loeb developed a semi-permeable membrane that made the desalination process known as reverse osmosis a practical and affordable way of making fresh water. As described by Prof. Oren, reverse osmosis requires a change in the direction that salt water naturally seeks. If you’ll allow an illustrative if inexact science lesson from a non-expert. Imagine a bathtub. Now imagine stretching a piece of fabric across the middle of the tub. You fill one half of the tub with seawater, and one half with fresh water. The tendency will be for the fresh water to migrate across the fabric “filter” and mingle with the salt water, producing a solution (called brine) that’s less salty than the seawater, but more salty than the fresh water. This is because nature likes to achieve equilibrium whenever it can – substances will move across areas of high and low concentration until uniformity has been achieved.
That process is called osmosis. Reverse osmosis does the what the name implies – it turns osmosis on its head and creates conditions where two solutions will move away from equilibrium. To achieve this, instead of using a “dumb” filter placed between two bodies of water, reverse osmosis uses a smarter semi-permeable membrane which allows only smaller water molecules to pass through. But a water molecule’s instinct is to head into the salty area to help dilute it. To get it to go in the other direction, reverse osmosis applies energy to “push” salt water through the filter into the area of fresh water. This process extracts fresh water from the salt water, leaving the salt behind. Scientists had been aware of reverse osmosis for centuries, but achieving it on a useful scale had escaped them, because forcing sea water to go “uphill” through existing membranes required a lot of energy – too much energy to be practical.
Prof. Loeb’s breakthrough was the development of a new kind of semi-permeable membrane, and a new, energy-efficient way of pushing seawater through it.
The new methodology involves much in the way of advance electro-chemical engineering, but suffice to say that the method took off, and according to Prof. Oren, it’s the recognized around the world as the most advanced, efficient way of freshening seawater in use today. And we should hope that the trend toward Prof. Loeb’s methodology continues.
“Around the world, water is still being desalinated by simple distillation, especially in oil-rich countries, which can afford the fuel to boil water,” says Prof. Oren. “But they’re changing, because water is going to be the big challenge of the next century.” Prof. Oren points out that in places like Saudi Arabia, and even in his own home town south of Tel Aviv, desalinated water is the sole source of drinking water. Israel’s Ashkelon plant is the world’s largest reverse osmosis facility, producing 320,000 cubic meters of fresh water every day – meeting the needs of roughly 100,000 people.
