New method turns ocean water into drinking water, without waste
A new solar-thermal desalination method that claims to turn seawater into drinking water “without waste” is drawing interest but also skepticism. Commenters note that while producing solid salt instead of brine could ease some environmental concerns and enable mineral recovery, the process still faces hard limits on energy efficiency, questions about cost, scaling, and durability, and may end up better suited for niche or small-scale use than for replacing conventional reverse osmosis plants. Broader concerns center on press-release hype, realistic brine management, and whether such technologies can be deployed at the scale needed for water-stressed coastal regions.
Nature of the claimed breakthrough
- Thread notes this is a University of Rochester solar-thermal desalination approach using a specially textured “black metal” surface.
- Key lab result cited: ~10 L/m²/day freshwater plus ~0.38 kg/m²/day salt under test conditions, with desalinated water below WHO/EPA salinity limits.
- Core novelty: capillary structure that moves salt away from the evaporating surface to a passive region, aiming to avoid fouling and allow solid-salt collection.
Brine, salt, and the “no waste” claim
- Many commenters dispute “without waste,” arguing solid salt piles are still waste and likely exceed any realistic market for salt.
- Others counter that solid salt is easier to manage than brine in some contexts and can at least avoid local “death zones” from concentrated discharge.
- Debate over whether crystalline salt disposal is actually harder than diluting brine and returning it to the ocean.
Energy efficiency and comparison to existing tech
- Several point out desalination has a thermodynamic minimum; reverse osmosis (RO) is already ~2–4× that limit and fairly efficient.
- Some argue the real comparison should be: solar thermal panels vs. using the same area for PV powering RO.
- Others stress economic and operational simplicity may matter more than peak energy efficiency, especially for low-skill, distributed setups.
Feasibility, scaling, and materials
- Strong skepticism that a lab-scale glass setup with femtosecond-laser-treated metal will scale cheaply or robustly.
- Concerns about salt slowly coating the active surface, fragility of nano-structured coatings, cleaning logistics, and need for complex enclosures or cooling.
- Prior “clog-free” solar desal prototypes (including from other universities) are noted as having little visible follow-up.
Byproducts and mineral recovery
- Some see potential value in solid salt for recovering magnesium, lithium, and sulfate, possibly offsetting costs.
- Others emphasize extraction is chemically and energetically nontrivial; cheap mined ores still dominate.
Environmental and ocean impacts
- Long subthread on brine toxicity: coastal discharge can create local dead zones, especially in shallow or semi-enclosed seas.
- Counter-argument: with sufficient dilution, deep/offshore discharge, or mixing with sewage/fresh seawater, impact can be negligible; this is framed as a solvable engineering problem.
- Disagreement over whether such mitigation is routinely done vs. ignored by cost-cutting operators.
Alternatives and broader context
- Some argue improving rainwater capture, groundwater management, and wastewater treatment is often cheaper than desal.
- Dehumidifier/“water from air” schemes are discussed and largely dismissed as energetically and volumetrically inefficient compared to desal.
- Political/economic obstacles (NIMBY opposition, lack of infrastructure investment, cost of nuclear vs. solar) are cited as bigger barriers than physics.
Meta: skepticism of university press releases
- Multiple comments criticize exaggerated titles and claims like “no waste,” urging more rigorous, less hype-driven communication from universities.