More Fresh Water With Less Energy

Solutions to environmental challenges are often laden with paradoxes. Let’s take the case of desalination of sea water to make potable water. It’s becoming more common in some parts of the world, including the Mediterranean region and Australia. But there’s a catch: it’s energy-intensive, therefore carbon intensive, and for that reason it ends up contributing to the climate change cycle.

The fact is that water factories, as desalination plants are also called, will become a more prominent feature of utility services in the future. Water scarcity is a growing global problem which will require local solutions. The figures vary but more than one billion people have inadequate access to potable water and the figure doubles in relation to sanitation. This will have a worrying impact on food production as the population grows. So why are we not doing more to tackle the problem?

“There’s a perception that water is omnipresent and free. But people are starting to realize it’s becoming a progressive problem”, said Thomas Rooney, CEO of energy-efficient desalination company Energy Recovery, during an interview to Energy Refuge at the Ontario Global Water Leadership Summit that took place on May 17 -18 in Toronto. “All too often we get a reprieve from the droughts. But one winter of rain doesn’t mean the range of water consumption is done with.”

Rooney, who also has vast experience in the renewable energy industries, knows well the issues related to the water/energy nexus. “Our product makes desalination more energy efficient. If you used inverted osmosis and didn’t use our device, the amount of energy required would be 2.5 times higher. 60% of the energy costs go away with our product”, he said.

Their product is called Pressure Exchanger (PX), and it takes all the water that doesn’t go through a membrane, which is 60%, and recovers all the pressure and energy that it stores. “You can let it go back to sea and lose all the potential energy, or try to recover it. We circulate the energy back in”, Mr. Rooney explained.

The Pressure Exchanger is a ceramic pump based on a rotary positive displacement pump that does the energy recovery work Mr. Rooney described above. The reduced cost of desalination has created a boom for the industry worldwide.

Energy Water Nexus

As the water issue becomes increasingly important, and investments in the sector are expected to parallel renewable energy financing, one question that arises is: how can the two sectors work together to create sustainability for both of them? In fact, are they attempting to do that?

“On one side we have a lot of smart people trying to solve the energy crisis. Separately we have an equally smart group trying to solve the global water crisis. And all too often you’ll find people fixing one side of the equation doing harm to the other”, Mr. Rooney said.

“A few years ago people thought ethanol would be great as an energy solution. Now we understand the water footprint for ethanol is unacceptably high. Conversely, you could look at certain water solutions such as thermal desalination, which is done in the Middle East, and it’s got a huge energy footprint. More and more the smart money is looking at where the two overlap. If it’s an energy solution it has to have a benign water footprint and if it’s a water solution it has to have a benign energy footprint”, he said.

Now that desalination has become more energy efficient, is it possible that it could one day become energy neutral or even energy positive? “If you’re trying to create potable water it’s impossible to be energy neutral because you’re trying to overcome one of the principles of physics and chemistry and that is osmotic pressure. But in places like Australia and Southern California people build a like amount of renewable energy in the form of solar and wind. For every MW of power it takes to run a desalination facility, you go out in the California desert and build a MW of power generation”, he said.

But there is, in fact, one way of creating energy with osmosis. “You can run reverse osmosis backwards and create osmotic power. You can take the exact same pressures you have to overcome when you desalinate water to actually create clean renewable energy. You look at the point where a fresh water river runs into an ocean. You can put fresh water with sea water and generate power because the salt wants to migrate from one to the other. So the reverse of desalination is actually energy creation. But you can’t have energy creation and desalination at the same time.

So there you go, as far as desalination and energy creation go, you can’t have the cake and eat it too. “No”, Mr. Rooney said. “But it would be wonderful if you could.”

Watch excerpt of interview with Thomas Rooney:

Article by Antonio Pasolini, a Brazilian writer and video art curator based in London, UK. He holds a BA in journalism and an MA in film and television.

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