Business, Science, Sustainability

Harnessing Energy Where Freshwater Meets Seawater

The spot where fresh and salt water meet, near Tasmania, could provide an alternative power source.
Fresh and salt water meet near Tasmania. Salinity gradients in areas like this could provide an alternative power source. Photo: jeaneeem | FlickrCC.

The key to combating climate change is reducing carbon emissions through alternative energy sources. We need to find ways to produce energy that doesn’t dump carbon into the atmosphere, and we could do a lot worse than looking at nature for inspiration. After all, the universe gets along without destroying itself rather well. Salinity gradients are a natural feature that might provide clean energy.

The term refers to the meeting of water with different levels of salt, such as when a freshwater river meets the sea. Acceding to a recent study by scientists at Griffith University in Queensland, Australia, harnessing salinity gradients could provide a renewable source of clean energy. Harnessing that energy would help to mitigate climate impact by reducing our reliance on fossil fuels, and could help improve processes in the desalination industry.

Getting energy in this way would require a process called Pressure Retarded Osmosis (or PRO), which basically involved passing water through a membrane that helps separate water of different salinities. This creates a solution that, after being depressurized via turbine, can be used to provide electricity.

As an added benefit, the process makes use of brine, which is a byproduct of the desalination process that is otherwise hard to put to use. The study suggests that osmotic plants could be built on rivers, especially in places like Australia, where most major cities sit at the meeting point of rivers and the sea. In fact, many of the world’s largest cities are in similar positions, so osmotic plants could pop up all over the place.

The question of just how efficient such plants would be remains unanswered, as the team has more research to do, but they think there’s a future. At the very least, as the process generates electricity almost as a byproduct of desalination, such technology could at least help reduce desalination plant’s reliance on fossil fuels.

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