Science Japan inaugurates its first osmotic power plant

Osmosis is a simple yet powerful natural process: water naturally moves through a thin, semipermeable membrane from areas of lower salt concentration to areas of higher salt concentration, attempting to equalise the difference. Imagine a glass split in two by a delicate filter. On one side, you pour fresh water; on the other, salty water. Because the salt cannot pass through the divider, the fresh water slowly seeps across to the salty side, diluting it. Osmotic power plants harness this everyday process to generate energy. They place fresh water and seawater on opposite sides of a specialised membrane. The seawater is kept under light pressure, and as the fresh water flows through to the saltier side, the added volume increases the pressure further. That extra force is then directed through a turbine attached to a generator, creating electricity. At the new Fukuoka facility, both freshwater and treated wastewater are used to combat seawater. As the saltwater side builds pressure and its salinity drops, some of that water is pushed through a turbine, steadily producing power. Japan's plant is only the second of its kind in the world. The first was completed in 2023 in Mariager, Denmark, by the startup SaltPower, as explained by Professor Sandra Kentish of the University of Melbourne. While the Danish site broke new ground, the Japanese facility is larger, even though its actual operating capacity is similar, according to Dr Ali Altaee. Smaller pilot projects have also been trialled in places such as Norway and South Korea.

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