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Scientists cook up new recipes for taking salt out of seawater

phys.org

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Re: Scientists cook up new recipes for taking salt out of seawater

#31

Post by inetknght »

amelius wrote: post #30
Retric wrote: post #6

Earlier quoted context omitted.

Desalination is cheap in day to day terms, it’s the scale of water we use that’s the issue. Sure, we can get ~1,000 gallons of drinking water for 3$ via desalination. That works out to a monthly water bill increase of ~45$ for a family of 5. Unfortunately, crops need incredible amounts of water. So, growing corn etc with desalination would case food prices to ~quadruple.

Since seaweed can grow on salt water, can we perhaps engineer other crops to do the same?

That sounds like a recipe to completely destroy the land, for _any_ other crops, on which saltwater crops are farmed.

Re: Scientists cook up new recipes for taking salt out of seawater

#32

Post by fghorow »

Having fancy chemistry as in the article is great, but there already exist thermal desalination solutions that require heat (e.g. geothermal, industrial waste heat) rather than work (e.g. electricity for R.O.). For example MED: " rel="nofollow">https://en.wikipedia.org/wiki/Multiple-effect_distillation> or MSF: " rel="nofollow">https://en.wikipedia.org/wiki/Multi-stage_flash_distillation....

Steam is not required for MED. Hot water ORC driving RO seems to be most efficient in some situations " rel="nofollow">https://www.mdpi.com/1099-4300/17/11/7530>, but MED is a simple, no-moving-parts solution that is also efficient.

Re: Scientists cook up new recipes for taking salt out of seawater

#33

Post by Retric »

amluto wrote: post #22
Retric wrote: post #11

Earlier quoted context omitted.

Sewage and distribution is not included in these costs. Current systems get water for almost nothing it’s mostly distribution and sewage systems that you’re currently paying for. As to why this is, a single pipe carrying 1,000x as much water costs no where near 1,000x much per foot. Each home might only need 1/10,000,000 the water, but it’s got to be built for peak demand not average useage. On top of this, people do…

None of this is at all relevant to my point. SFPUC charges over $4/ccf for wholesale water. This does not include distribution costs, and this is paid regardless of whether the water is sold, leaks, or is used for firefighting. If SFPUC’s wholesale customers purchased desalinated water and managed to escape their SFPUC contracts, they would eliminate this expense. edit: http://bawsca.org/water/rates/wholesale

That’s not exclusive price just per gallon of water.

https://sfwater.org/modules/showdocument.aspx?documentid=774...

Wholesale untreated water is 1.02$ per 1,000 gallons. Page 16: ( 0.76 per 748 Gallons delivered). Plus a fixed fee for the size of the pipe (22.67$ for a one inch pipe.)

Re: Scientists cook up new recipes for taking salt out of seawater

#34

Post by tobr »

inetknght wrote: post #31
amelius wrote: post #30

Earlier quoted context omitted.

Since seaweed can grow on salt water, can we perhaps engineer other crops to do the same?

That sounds like a recipe to completely destroy the land, for _any_ other crops, on which saltwater crops are farmed.

Assuming you would use salt water on existing land, but wouldn’t it open up for growing crops in new places, on/close to seawater?

Re: Scientists cook up new recipes for taking salt out of seawater

#35

Post by lostlogin »

Retric wrote: post #6
sayusyz wrote: post #3

"The current state-of-the-art in RO desalination works very well, but the cost of RO desalination driven by electricity is prohibitive," Why is taking salt out of sea water such a challenge?

Desalination is cheap in day to day terms, it’s the scale of water we use that’s the issue. Sure, we can get ~1,000 gallons of drinking water for 3$ via desalination. That works out to a monthly water bill increase of ~45$ for a family of 5. Unfortunately, crops need incredible amounts of water. So, growing corn etc with desalination would case food prices to ~quadruple.

> Unfortunately, crops need incredible amounts of water. So, growing corn etc with desalination would case food prices to ~quadruple.

Raising crops and live stock on deserts or other marginal farmland is a huge part of this.

Re: Scientists cook up new recipes for taking salt out of seawater

#36

Post by jdavis703 »

Retric wrote: post #6
sayusyz wrote: post #3

"The current state-of-the-art in RO desalination works very well, but the cost of RO desalination driven by electricity is prohibitive," Why is taking salt out of sea water such a challenge?

Desalination is cheap in day to day terms, it’s the scale of water we use that’s the issue. Sure, we can get ~1,000 gallons of drinking water for 3$ via desalination. That works out to a monthly water bill increase of ~45$ for a family of 5. Unfortunately, crops need incredible amounts of water. So, growing corn etc with desalination would case food prices to ~quadruple.

In California we grow water thirsty crops like rice and almonds. By substituting out for less water intense agriculture such price shocks could be reduced. There's also the whole issue of producing animal feed, which is inherently less efficient than just having humans eat the feed directly.

Re: Scientists cook up new recipes for taking salt out of seawater

#37

Post by hinkley »

Overtonwindow wrote: post #12

I don’t think the problem we should be focusing on is how to remove salt from water, but what to do with the salt after it has been removed.

Kim Stanley Robinson posits using salt or brine to keep the North Atlantic thermohaline cycle from stalling by dumping it into the subduction zone.

But that’s a lot of shipping. And I wonder if a better way is to capture the glacier melt runoff from Greenland before it can enter the ocean currents, and desalinate that brackish water. I’m not sure what the ratio of brine to fresh water is (ratio of boats in each direction) or the desal versus shipping costs.

Re: Scientists cook up new recipes for taking salt out of seawater

#38

Post by amluto »

Retric wrote: post #33
amluto wrote: post #22

Earlier quoted context omitted.

None of this is at all relevant to my point. SFPUC charges over $4/ccf for wholesale water. This does not include distribution costs, and this is paid regardless of whether the water is sold, leaks, or is used for firefighting. If SFPUC’s wholesale customers purchased desalinated water and managed to escape their SFPUC contracts, they would eliminate this expense. edit: http://bawsca.org/water/rates/wholesale

That’s not exclusive price just per gallon of water. https://sfwater.org/modules/showdocument.aspx?documentid=774... Wholesale untreated water is 1.02$ per 1,000 gallons. Page 16: ( 0.76 per 748 Gallons delivered). Plus a fixed fee for the size of the pipe (22.67$ for a one inch pipe.)

Curious. I’m pretty sure my water provider pays the BAWSCA rate. I don’t know why it’s so different.

edit: You’re looking at rate W-24. BAWSCA users seem to pay rate W-25, which is far higher. I don’t know exactly what the difference is.

Re: Scientists cook up new recipes for taking salt out of seawater

#39

Post by ChuckMcM »

This is a great paper, the really cool bit is that it seems fairly straight forward to convert this to a larger process. Basically add saltwater, warm it, take the settled part of the solution (which is now desalinated) out of the bottom, and the salt dense water out of the top, cool it and precipitate out the salt. Nothing has to evaporate everything runs at a normal vapor pressure so you aren't struggling with high pressure and low pressure domains.

I'd love to see if you could use spent nuclear fuel (which is an excellent heat source) to just run one of these things continuously for a couple of decades :-).

Re: Scientists cook up new recipes for taking salt out of seawater

#40

Post by justinator »

MuffinFlavored wrote: post #4
sayusyz wrote: post #3

"The current state-of-the-art in RO desalination works very well, but the cost of RO desalination driven by electricity is prohibitive," Why is taking salt out of sea water such a challenge?

Is it maybe easier to capture the rain that falls from the sky instead? The rain that falls from the sky is salt-free, right? It then becomes salty when it touches the ocean?

There's actually water rights/legal issues to this. For example until recently it was illegal for me to do this in Colorado; the law has changed to allow ~114 gallons/year.
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