Turning seawater into fresh water using electricity close to the thermodynamic minimum for the separation, so that desalination is no longer limited by its energy bill.
Scope
In: seawater desalination by membranes (reverse osmosis, electrodialysis) and the energy recovery and staging around them. Out: the membranes themselves, which are materials/high-selectivity-membranes; brackish and wastewater reuse, which start from much lower salinity and need less energy; and the power source, which belongs to the energy domain.
Specific energy consumption headline0.5 orders of magnitude to go
Energy used to produce one cubic metre of fresh water. Lower is better.
Current (2021-01-01)3 kWh m⁻³
Target1 kWh m⁻³
Limit–
Conditions. Seawater feed, electricity per cubic metre of fresh water.
Why this target. A round value chosen by the atlas, not set by an agency: about the level a simulation study reached for reverse osmosis on osmotically diluted seawater (0.96 kWh/m3), and a third of the current value, so that energy stops dominating the cost of desalinated water.
Note. Best value found in a measurement with natural seawater in this seed pass: multistage electrodialysis, not reverse osmosis. The abstract-level search did not find a measured full-scale reverse osmosis figure with a quotable number, so the true state of the art may be lower; a curator should replace this value with a full-scale reverse osmosis measurement.
Practical plants already work near the thermodynamic limit
highfundamental limitlayer: principleopen
Reversible reverse osmosis and electrodialysis consume the Gibbs free energy of separation, and the practical energy of both approaches that minimum only as the number of stages grows. Reviews state that most desalination technologies already work near their limit, so the remaining reduction is bounded and each step costs capital. The numeric value of the minimum is in the body of the cited papers and is not recorded here yet.
Reverse osmosis membranes trade water permeability against salt rejection. Analysis of biomimetic membranes indicates what a more permeable, defect-free membrane could offer for seawater desalination, but such membranes are not yet a commercial product.