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Comment by URSpider94 | Hacker News Reader

Desalination is not the answer.

As TFA mentions, desalination is incredibly power-hungry. Additionally, it creates ultra-salty brine as a byproduct, which is difficult to dispose of -- if you just dump it into the ocean, you'll kill fish.

Finally, desalination plants are a great option for supplying water when nothing else is available, but as soon as you can get water from pretty much anywhere else, they become extremely cost-inefficient. Take the case of Santa Barbara as a great example: drought from 1986-1992, built a desal plant for $34 million. Turned it on in March 1992, it ran until June 1992, and then it started raining ... hasn't been used since.

(http://www.santabarbaraca.gov/gov/depts/pw/resources/system/...)

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The FAQ at your link says that there is no problem with ocean disposal of the brine, which is only twice the concentration of normal seawater. If you dump that into the ocean, it will quickly be diluted and raise the salinity slightly. Got any evidence that the salinity increase will kill fish? If you filled a tank with the brine and dunked a fish in it, that might do it.

Sea grass and coral seems to be a bigger concern than fish, though some fish may be affected by salinity.

"Overall, it would appear that benthic infaunal communities and sea grasses are the most sensitive to the acute effects of concentrate discharge; some communities seem to be tolerant of effects of up to 10 psu increases, while others are affected by increases of only 2-3 psu. However, few studies have evaluated discharges to embayments, where less dispersion of the discharge may occur, and the chronic impacts on demersal vertebrates, particularly those which have significant life history behaviors (i.e., reproduction, migration) driven by salinity variations."

There are also many concerns with the effluent than just salinity.

http://www.swrcb.ca.gov/water_issues/programs/ocean/desalina...

California has lots of good sun, why not power the plant via solar power?

The brine can be evaporated into salt as well, right?

It seems to mean that problems like this have to be solved via an entire system and not via individual components.

The amount of energy required to evaporate water means you need a lot of sunlight (area) to evaporate a relatively small amount of salt water.

You can save a lot of energy by getting some water out of sea water, leaving extra-salty brine, rather than trying to get all the water out, leaving dry salt.

Look at Google maps satellite view around the south end of San Francisco Bay. Those are salt water evaporators run by Cargill [1].

Desalination brine could be a big increase in efficiency for them in place of ordinary sea water.

[1] http://www.cargill.com/corporate-responsibility/environmenta...

It is incredibly power hungry. The solution is more power. Breakthroughs in energy production. Or we could just do the obvious thing and build a lot more nuclear power, something we should have been doing for decades.

In the next 20 years, solar will take care of that problem regardless.

can that brine be used for other things? This might sound silly to a knowledgeable person, but isn't salt worth something?

If the infrastructure is available, it would be interesting to force things like watering lawns with only water from something like a desalination plant.

A study in 2000 found that a household in California used 132,000 gallons of water per year. 132,000 gallons of water weighs 550 tons, and seawater is 3.5% salt, desalinating 550 tons of water would (optimally) produce something like 20 tons of salt.

To supply 10 million households with drinking water from sea water, then, produces 200 million tons of salt. The current global salt market is 250 million tons, at a price of about $50 / ton. I find it unlikely that the market would bear dumping that much salt on it at a price that would make producing the salt worth it.

Disposal is probably a cheaper course.

The city of Chicago alone uses an average of 215,000 TONS of salt per year to melt ice..

http://www.wbez.org/series/curious-city/how-much-road-salt-e...

Obviously a little drive, but salt prices are high up here ;)

The current salt market is based on a supply of actively produced salt. Only ~7%* of worldwide production is "solar salt", derived from evaporating sea water. The rest is actively mined or extracted by other methods.

Dumping 200 million tons of new "solar salt" on the market would collapse prices and signal the end for the existing player in the salt industry. I don't think this would be an issue in the long term as salt derived from a hypothetical mass-desalinization industry is essentially free. Replacing heavy industry with the byproduct of an essential and beneficial process is the very definition of economic and environmental efficiency.

California gets a secure water supply, consumers and industry get cheaper salt, and the imprint of the salt mining industry is no longer a concern in the environment.

*Source: http://www.saltinstitute.org/salt-101/production-industry/

I don't know the source of salt in solar powered molten salt steam plants. Maybe this brine could be at the front end of that production process?

Solar thermal plants use a working fluid that happens to be sometimes called "salt" but is a totally different thing from the salt that is in ocean water.

This. Gibraltar built a desalination plant because it was the only option - the Spanish refuse to pump water over the border for political reasons.

They relied on a moisture condenser built into the side of the rock initially (there is often very moist air caused by the cold air from the atlantic hitting the warm air from the med), but with expansion it wasn't enough and is now used primarily to provide irrigation to the nature reserve.

iirc the desal plant was disassembled and sold to Saudi Arabia sometime in the 90's. I have no reference for this at the moment.

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