Japan has opened its first osmotic power plant

How the plant actually works

• Commenters clarify the key point: the osmotic plant is colocated with a desalination plant.
• It uses:
  • High-salinity brine from desalination as the “salty” side.
  • Partially treated wastewater (low salinity) as the “fresh” side.
• As the two streams mix across membranes, the system:
  • Recovers some energy from the salinity gradient.
  • Dilutes the brine before discharge, lowering environmental impact.
• This is likened to a recuperator or regenerative braking: harvesting energy from a process that would otherwise waste it.

Efficiency, scale, and economics

• From the reported 880,000 kWh/year, commenters infer an average output of ~100 kW; rough estimates suggest this offsets ~5% of the desalination plant’s power use.
• Many see it as “making desalination ~5% more efficient” rather than a standalone power source.
• Several question whether it’s better to:
  • Fully treat wastewater to drinking quality and desalinate less seawater instead, or
  • Simply dilute brine with wastewater without bothering to extract energy.
• Others argue pilot projects are needed to get real-world data on costs (CAPEX/OPEX) and performance before judging.

Water reuse, psychology, and alternatives

• Thread notes strong public resistance to “drinking treated sewage” even when technically safe, leading cities to dump treated water to rivers/oceans and then build desal plants.
• Osmotic power is seen as a way to get extra value before that discharge.
• Some worry it “wastes” low-salinity water for a small power gain; replies say local hydrology and excess wastewater can make this acceptable but site-dependent.

Environmental and broader energy context

• Better brine management (less-saline discharge) is viewed as a significant co-benefit.
• One subthread contrasts osmotic power (energy recovery) with solar/wind (new energy input).
• Another spirals into whether nuclear is “renewable,” debating fuel exhaustion, breeder reactors, costs, safety, and regulation, but this remains tangential to the osmotic project itself.