> RO desal splits the incoming ~3% salinity stream into two halves, one fresh and one ~6% salinity. This concentrated brine is fed to adjacent brine processing facilities (ideally in both countries) that exploit the region’s abundant solar and geothermal energy to extract potentially millions of tonnes of lithium, sodium, magnesium, chloride, and other metals found in sea water. The resulting depleted brine is piped back to the ocean where it is thoroughly mixed with sea water and discharged.
Casey's proposing we mine the brine for useful minerals. You're right he's glossing over details, but a citation addressing the economics of brine disposal with his proposed processing would add more to the discussion.
We just simply don't need that much brine for useful minerals -- it's a huge cost and you'll be left with massive piles of mostly useless salt.
On one of my hard drives, I've got an engineering / construction plan for a moderately sized intake + discharge for a small RO facility that would've passed muster in Australia, which has pretty reasonable environmental protections. Round numbers - the intake would have cost $25 million and the discharge more like $75 million. You need a massive structure to be able to emit that brine back into the environment in a way that doesn't just nuke the surrounding marine life. Huge pipes + check valves + cascading discharges, all either on the ocean floor if there aren't reefs and other sensitive areas or even worse from a cost perspective, tunneled out to a depth that can handle the amount of salt.
Seawater is ~35g/L of TDS - the author is talking about 5 million acre feet of desal - what's that, 20 million tons of salt annually?
This is doable. Many coastal wastewater systems already have large pipes that extend miles to sea (1), and that's a rounding error compared to the many more miles of pipe routing sewage to the plant (2, pg A-3)
“ In general, anthropogenic activities pollute the coastal marine environment, altering the environment’s physiochemical properties and resulting in changes in marine communities. Physiochemical conditions can be altered by the presence of pollutants, hypoxia, organic enrichment, decreased hydrodynamic conditions, and, more recently, brine discharge (de-la-Ossa-Carretero et al., 2016). Salinity elevation in receiving soil and water bodies and the territorial consequences of brine with high total dissolved solids on benthic marine life close to the discharge site are the most important environmental challenges associated with brine disposal (Miri and Chouikhi, 2005; Panagopoulos et al., 2019).”
Lots more detail in the article on studies of specific populations as well as discussion of mitigations and alternatives.
This guy claims that Lithium may be partially responsible for some weight gain in our population, but also, that desalination plants cause extra lithium as well.
If it was mined out, that would be viable, but if not...
Considering that the brine output of a single large-ish plant might be 150,000m³ per day[1], that's a hell of a mine shaft to take it continuously. The rock with the same volume as a day's brine would weigh a million tons. The entire Aberfan spoil tips were only 2 weeks worth of that much volume (2 million cubic metres).
The gigantic Hambach open-pit mine grows by 0.3km³ a year, so that could take it (but it can't take the Saudi million m³/day plant). By the time the mine is depleted, the resulting 18km³ pit would not be filled by our single hypothetical plant for over 300 years, assuming it won't evaporate. Which leads to:
The evaporation pools might work: they'd "only" have to be 3000 acres (12 km²) to gather the 4GW of solar power at 1kW/m² for 8 hours a day to continuously evaporate that much water daily[2]. Which is certainly large, but not completely impossible. But then there's 2 million tonnes of salt per year which will accumulate continuously over time.
[1] the largest is over a million
[2] not including water not bring a perfect absorber of solar energy or differing insolation
In an environment where solar and geothermal electricity are abundant enough to make this work, it would be far easier to condense water straight from the air by refrigeration.
:D and if you scale this to the point where the amount of water vapor in the atmosphere is affected, you can also use some of the abundant energy to boil the ocean to replace that water vapor. :) Same net effect (water is taken from the ocean and salt is not) without actually moving the salt back and forth.
Casey's proposing we mine the brine for useful minerals. You're right he's glossing over details, but a citation addressing the economics of brine disposal with his proposed processing would add more to the discussion.