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Desalination: Making the Ocean Drinkable

From Tiny Dynamo: How One
of the World's Smallest Countries Produces Some of the Most Important Inventions
, by
Marcella Rosen

This energy-efficient method of desalination is a breakthrough in creating fresh water internationally.

 

Yoram Oren’s work is unnatural.

As a member of Ben-Gurion University’s Department of Desalination & Water Treatment, Professor Oren’s job is to make water turn against its very nature and go places it doesn’t want to go.

“Nature seeks equilibrium,” he says. “Desalination, separating the salt from sea water to make fresh water, is an act of overcoming what nature is seeking. It’s not easy.”

It’s not easy, but as the earth becomes more crowded and there simply won’t be enough naturally occurring fresh water to go around. We’re going to have to get more of it, and the only feasible way to do this is to make it from sea water. Over the next 10, 20 or 50 years, desalination will become not only important but compulsory.

But while the rest of the world is just waking up to the idea that desalination will become a way of life in the years to come, desert countries have been relying on desalination for decades, because they’ve had to.

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 hometown 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.

That dependence is only going to grow, and even countries that are profligate with their resources are coming around to water treatment through reverse osmosis – especially since, Prof. Oren and others in his field are starting to realize how much more reverse osmosis can achieve.

“The environment is telling us to find more efficient ways to treat not just saltwater, but all our wastewater, agricultural runoff, and municipal water,” he says. “We’re working on making membranes that are more and more sophisticated because now we have to protect them not only from salt, but from organic compounds, inorganic compounds, bacteria, viruses, proteins, sugars, all the stuff you find in the different kinds of waters we’re treating.”

Industrial-scale reverse osmosis is becoming the norm in places from Malaysia to Spain – which, according to Prof. Oren, seems to be in a friendly competition with Israel to build the world’s largest desalination plant. Spain is also currently building 20 desalination plants, which will handle about one percent of the country’s total water needs within just a few years.

Between the demands of population growth, increasing energy consumption and more people wanting a better way of life, conditions on Planet Earth are changing. Right now, the shape and tone of the lives we’ll lead in the future are up for discussion. But some things are essential, and none of those is more vital than clean fresh water – and lots of it. While the rest of us come to terms with how we want to live life in the future, Prof. Oren and his colleagues are building on the work of Sidney Loeb to ensure that we’ll have the water we need to live it.