The plant, operated by the Fukuoka District Waterworks Agency, marks Japan as only the second country in the world to deploy this technology after a Danish company pioneered it in 2023, according to Kyodo News. Local officials and experts present the project as a breakthrough for renewable energy that can run around the clock, unaffected by weather or sunlight, and without emitting carbon dioxide. “I feel overwhelmed that we have been able to put this into practical use. I hope it spreads not just in Japan, but across the world,” said Akihiko Tanioka, professor emeritus at the Institute of Science Tokyo, in comments to Kyodo News.
Beneath its understated exterior, the Fukuoka facility relies on a process known as salinity gradient power. Treated sewage water and highly concentrated seawater are separated by a special permeable membrane, triggering osmosis as water molecules move toward the higher salinity side. The resulting water pressure spins a turbine, which in turn powers a generator.
The plant is expected to generate approximately 880,000 kilowatt-hours of electricity annually, according to the Fukuoka District Waterworks Agency. That energy will directly support a local desalination plant supplying fresh water to Fukuoka City and neighboring areas—tying the renewable energy project closely to local water infrastructure.
Seriously awesome waste energy recovery system. Based on my read, this seems best used as an energy recovery solution at desalination plants where a portion of the energy used for the RO can be recovered via the reverse process of diluting the brine. Unfortunately in many places where desalination is used it is likely more efficient to reproduce the wastewater stream rather than dilute the brine, as water is the resource in shortage, HOWEVER there are clear cases where contaminated waste streams that can’t be used for human consumption or ag use could be used for the purpose with the side benefit of concentrating the contaminant stream to better manage containment, think nuclear waste dioxins mercury or PFOS where release into the environment as a waste management strategy is disallowed.
Speaking of nuclear, this makes me wonder if this could be a step in the waste management of liquid salt used in liquid salt reactors. They say the liquid salt is reusable for a long life, but I do wonder if there isn’t some level of need to replace the salt or refine it periodically, maybe this could play a part in that process? Anyone have info?
Could you please explain this part? My first thought was “hey cool, they can use the brine from the desalination plant,” but I guess I was wrong. I thought they would just dilute the brine with treated waste water, then dump it in the ocean, refill the PRO plant with brine from the nearby desalination plant.
Basically in areas where desalination is used for mass water production pure water is the resource in shortest supply and therefor osnhigher value than electricity. Wastewater is a potential source to feed RO systems to generate pure water, any water source with a lower concentration of solute than seawater is a potentially more efficient feedstock for the RO purification than seawater. Given that RO purification takes more energy than the energy generation system discussed here, it would be more efficient and therefore cost effective to mix the wastewater into the feed stream and produce a less concentrated brine waste output rather than use it to dilute the brine waste after the fact. The more concentrated the brine output from an RO plant, the more energy it takes to produce due to diminishing returns as the osmotic pressure increases with solute concentration.
There are exceptional cases, as I mentioned, where the composition of the wastewater stream will make it so that concentrating the solute in that stream has an economic incentive greater than the demands for RO water. In those cases diluting the brine may make economic sense. The location of the plant impacts this as well, there may be some edge cases where transporting the brine to the source of wastewater and processing it there on site may have an economic advantage. I’m thinking of nuclear waste and high toxicity chemical plant waste here where release is not an option and storage is mandated, so the waste stream will need to be both segregated from other less toxic waste and stored long term.