塩分濃度２倍の「濃縮海水」　水不足に悩まされた都市にしかない副産物で「発電」　日本初

Fukuoka City, which has long suffered from water shortages, has a facility that converts seawater into freshwater. For many years, the "concentrated seawater" produced when producing freshwater from seawater has been discarded. Japan's first attempt to utilize this concentrated seawater to generate electricity is now underway. ◆ "Osmotic Power Generation Using Differences in Salinity" Fukuoka City Mayor Soichiro Takashima "We can generate energy here by using wastewater, which we previously discarded." The Fukuoka Waterworks Authority, which supplies water to the Fukuoka metropolitan area, announced "osmotic power generation" on the 6th. This is the first such example in Japan and the second in the world. Fukuoka Waterworks Authority President Takahisa Nakamura "We generate electricity by utilizing the difference in salinity." "Osmotic power generation" utilizes the difference in salinity between "concentrated seawater" produced when freshwater is extracted at a desalination center and treated sewage water. Only water passes through the osmosis membrane to the seawater side, increasing the amount of high-pressure water, which in turn rotates the waterwheel and generates electricity. ◆ Desalination facility built in drought-stricken Fukuoka Without a major water source, the Fukuoka metropolitan area has frequently suffered from droughts. Since 2005, the "Mamizu Pia" seawater desalination center has been operating, extracting freshwater from seawater. Koichiro Ono, Operations and Management Section Chief, Fukuoka District Waterworks Corporation "The system extracts freshwater from seawater by applying strong pressure to it." When pressurizing seawater and utilizing special membranes to supply an average of 20,000 tons of freshwater per day, the result is "concentrated seawater." ◆ "Concentrated seawater" with a salinity of approximately 8% RKB Reporter Takashi Imabayashi "This is concentrated seawater coming out of the tap. As you'd expect from the word "concentrated," when you taste it, it's significantly saltier than regular seawater." "Concentrated seawater" has a salinity of approximately 8%, double that of regular seawater. Until now, it has been diluted with treated sewage water before being released into the ocean. Takahisa Nakamura, President of the Fukuoka District Waterworks Authority "If we can use it for osmotic power generation, rather than just mixing it all together and throwing it away, we can really make use of this untapped resource." ◆Power generation facility scheduled for operation in 2025 The power generation facility will be constructed by Kyowa Kiden Kogyo, a water treatment plant manufacturer, at a cost of 700 million yen. The Waterworks Authority will provide the land and concentrated seawater, and it is scheduled to begin operation in April 2025. The annual power generation capacity will be enough to power 300 average households (approximately 880,000 kilowatt-hours), equivalent to the output of solar panels covering the area of ​​two soccer fields. This will provide a stable power source that is not affected by the weather. ◆Establishing the dream technology to generate electricity from seawater Furthermore, based on the experience gained with concentrated seawater, we aim to establish technology to generate electricity from ordinary seawater in the future. Fukuoka City Mayor Soichiro Takashima "As energy conversion efficiency improves, this is a challenge we are taking on with an eye toward growing significantly amid the current challenges of decarbonization and energy." If realized, this is a "dream technology" that would enable electricity generation from inexhaustible seawater. Fukuoka, a region with scarce water resources, operates its seawater desalination center at great expense. It will be interesting to see whether this experience can be leveraged to create a world-changing technology.