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Why is desalination so difficult?

practical.engineering

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Re: Why is desalination so difficult?

#311

Post by frumper »

function_seven wrote: post #299
rs999gti wrote: post #288

Earlier quoted context omitted.

There are no water pipes from the coast to the central valley? I wonder if NIMBYism blocked that? And if an agency wanted to transport water like the USA national oil pipeline system, would they be blocked similarly?

There are aqueducts between the CV and coastal areas. The water goes the other direction. If desalination becomes widespread, I imagine the water not shipped to the coast could remain in the Central Valley. I don’t know one way or another if this would make political or economic sense. EDIT: Wikipedia has a good overview: https://en.m.wikipedia.org/wiki/Water_in_California

Water rights are so complicated that they’d probably sell the water to the Central Valley before it ships to them. I think it very unlikely that they’d give them up.

Re: Why is desalination so difficult?

#312

Post by codedokode »

The author have mentioned that water with more than 1-2 promille of salt is considered not drinkable. But I have a bottle of carbonated mineral water from the mountains and the label says it contains 6-9 g of salts per 1 liter. So I guess it depends on which salt it is.

Also, the author mentions that people in US use 1100 liters per day (which is too much in my opinion), but not all this water needs to be drinkable, one probably can not drink more than 3-4 liters per day, and the rest of the water can be salty.

Re: Why is desalination so difficult?

#313

Post by ftxbro »

luhn wrote: post #309
ftxbro wrote: post #253

Earlier quoted context omitted.

Does this mean I can buy watery maple syrup that is 2x watery for less than half the normal cost like maybe a quarter of the cost? Or does the volume and weight for shipping and handling offset that savings or does no one want watery syrup so there is no market so they don't make it?

I think you're overestimating how much you could save. Rule of thumb is that it takes 40 units of sap to make one unit of syrup. (But this can vary widely depending on the sugar content of the sap.) So making syrup at half the concentration would require removing 38 units of water, instead of 39. That's not going to make much of a dent in the processing costs.

bro the more concentrated the syrup the harder it is to remove the next unit of water, that's why i was asking maybe provide a product that stops while it's still a little watery and not have to do the last whole stages

Re: Why is desalination so difficult?

#314

Post by codedokode »

gamegoblin wrote: post #77

I was surprised how cheap it is. Desalinated water costs ~50 cents per 1000 liters [1]. That's about the same amount of water as a typical American household uses per day. 50 cents per day for a fully desalinated water supply is... incredibly cheap. If you're interested in water policy and water management / engineering, I cannot recommend enough reading the book "Let There Be Water: Israel's Solution for a Water-Sta…

As I understand, before getting 50-cent water you need to pay a billion dollars upfront. Why so expensive?

Re: Why is desalination so difficult?

#315

Post by ShadowBanThis01 »

ericlewis wrote: post #125
lisper wrote: post #88

Earlier quoted context omitted.

You've pretty much nailed it except for one minor nit: > It takes less energy but produces a concentrated liquid waste stream that must be disposed of. This implies that creating a concentrated waste stream is a problem unique to reverse osmosis. It isn't. No matter what you do you're going to end up with a bunch of salt that you have to get rid of somehow.

good thing people need salt!

With enough desalination, the Romans will be able to afford a huge army!

Re: Why is desalination so difficult?

#316

Post by codedokode »

iudqnolq wrote: post #120
Veserv wrote: post #112

Earlier quoted context omitted.

Freshwater withdrawals per capita in the US (which includes agricultural exports and animal feed such as alfalfa sent to Saudi Arabia) are around 1550 cubic meters per year. https://ourworldindata.org/grapher/water-withdrawals-per-cap... So that is around $775 per person per year assuming no net change in water use. In contrast, Germany uses around 410 m^3, France around 475 m^3, and Australia around 724 m^3, so the…

That equates to around 4,000 liters per person per day. Freshwater withdrawals is a very broad category, it also includes water released to turn hydropower turbines. But it's also unfair to compare across countries without taking into account water sent between countries in the form of produce and products.

4,000 liters per day is too much. It is 10 full bathtubs. Do Americans leave the tap open or do they take a bath 10 times per day?

Re: Why is desalination so difficult?

#317

Post by tguvot »

janalsncm wrote: post #287
tguvot wrote: post #138

Earlier quoted context omitted.

desalination plants are built to produce specific amount of water in order to cope with demand. if you going to stop desalinating while there is no solar, you need more plants in order to desalinate more water during the day. also, in general, even during day, solar not always available.

Sure. So if for example your city has an average of 3400 hours of sun per year like Jerusalem does, and you know how much water you need to produce in the 8760 hours of the year, you can calculate how much to desalinate during sunny hours. Excesses can be used for excess water or sold back to the grid.

desalination plants don't serve one city. they serve country. also, in general, it's not economical to build plants that do not work 24/7 unless you are country that can spend x3 to overbuild and keep equipment idle

Israel btw supplies desalinated water to Jordan and PA.

Re: Why is desalination so difficult?

#318

Post by TheDudeMan »

codedokode wrote: post #312

The author have mentioned that water with more than 1-2 promille of salt is considered not drinkable. But I have a bottle of carbonated mineral water from the mountains and the label says it contains 6-9 g of salts per 1 liter. So I guess it depends on which salt it is. Also, the author mentions that people in US use 1100 liters per day (which is too much in my opinion), but not all this water needs to be drinkable,…

Does one feel clean after bathing in salty water? Maybe. Not sure.

Re: Why is desalination so difficult?

#319

Post by FredPret »

hansvm wrote: post #265
FredPret wrote: post #249

Earlier quoted context omitted.

It might just cause earlier rainfall, not more of it. There's x amount of water in the atmosphere, and you can't add more by spraying salt crystals.

You can though. The amount of precipitation (averaged over a long enough period of time) is inversely proportional to the amount of evaporation and other water entering the atmosphere (averaged over a long enough period of time). Note that the two things being compared are _rates_ not _masses_. If all you do is cause water to fall sooner then: 1. The humidity in the air drops, increasing evaporation rates because of…

Ah yes, that actually makes sense. Making the air drier speeds up the entire water cycle, thus more rainfall.

It would be interesting to have a water cycle simulation with sliders.

Re: Why is desalination so difficult?

#320

Post by fsckboy »

myshpa wrote: post #310
fsckboy wrote: post #293

Earlier quoted context omitted.

is this true? I can understand why it would be true, but "sea salt" is a real thing that's been traditionally made in seaside communities through to today, and I find it hard to believe they're cleaning it at anything finer than a gross scale. https://en.wikipedia.org/wiki/Fleur_de_sel

Microplastics found in 90 percent of table salt https://www.nationalgeographic.com/environment/article/micro... The presence of microplastics in commercial salts from different countries [2017] https://www.nature.com/articles/srep46173 Global Pattern of Microplastics (MPs) in Commercial Food-Grade Salts: Sea Salt as an Indicator of Seawater MP Pollution [2018] https://pubs.acs.org/doi/10.1021/acs.est.8b04180 Micropla…

thank you for the information, for sure, but i was responding to the claim that sea salt "needs cleaning" to point out that that seasalt isn't being cleaned, so it puts an upper bound on the value of need as it concerns the commercial market including govt regulation. My suspicion was that where would be more to worry about from single-celled life detritus, heavy metals, forever chemicals etc, but the marketplace doesn't seem to be worried about that.

I go about my daily life not worrying about microplastics (I know they are ubiquitous, and I'm not in favor of them, I just don't worry about them) Are microplastics known to cause particular diseases, or just suspected on the grounds that they "couldn't be good"? plastic is pretty inert which is why it remains around for so long, and while it is made from toxic things, it's generally considered safe. I'm just curious about actual microplastic effects rather than the sort of "it's estrogenizing our boys, antivax...er-plastic" suspicions.

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