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Why is desalination so difficult?

practical.engineering

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Re: Why is desalination so difficult?

#301

Post by MarkusWandel »

giantrobot wrote: post #256
tylerag wrote: post #40

Earlier quoted context omitted.

They're concentrating maple syrup. It comes out of the tree with the sugar and flavors already dissolved in it.

Part of the flavor of maple syrup is due to caramelization and the Maillard reaction of components of the sap. Just concentrating the sap would get you a syrupy substance sourced from a maple tree but it wouldn't be maple syrup .

I've never liked the flavour of maple syrup very much. At the same maple syrup place visit, we had some, on pancakes. WTF? This is plain table sugar! What kind of stunt are you pulling here? The guy supervising the boil said don't you know? The very best grade is like that, hardly maple-y at all! Turns out it really was about the sugar all along, with the initially undesirable maple flavour coming to be prized over time as a side effect.

Re: Why is desalination so difficult?

#302

Post by throwaway14356 »

I was never able to find the publication again but I read an article one time about the work of 2 Australian professors (I forget which kind) who designed a giant circle shaped verical axle wind turbine with 2 tubes that suck sea water up along the sides and sprays it up in the air with the brine dropping near the turbine. An array of those they claimed could create dense clouds that produce a lot of rain at some (according to them) surprising ratio to cost.

Re: Why is desalination so difficult?

#303

Post by Terr_ »

jtriangle wrote: post #178
caseyohara wrote: post #92

Earlier quoted context omitted.

Deserts are far more alive and biodiverse than people think. > The Sonoran Desert encompasses 120,000 square miles of southwestern Arizona, southeastern California, and in Mexico, northwestern Sonora and most of the Baja Peninsula. With nearly 3500 species of plants, 500 species of birds, and 1,000 species of bees, the Sonoran is the most biodiverse desert on earth.

You do have to consider though, how important are those ecosystems? Because I see this often used as a reason we can't do something, but they never qualify it with reasons why one should care. I also pose this as a completely honest question, as I don't really know if you wiped out every desert ecosystem with solar/desal/etc if it'd actually affect anything else.

Separately from "is this desert ecosystem useful", I would assert that the biodiversity of stuff that survives in arid environments is immensely valuable, representing umptillion creature-years of evolutionary R&D.

Even if our descendants committed to turning Earth into a uniformly-lush garden world, think of its value in terraforming other planets, or even just novel biochemistry and adaptations.

Re: Why is desalination so difficult?

#304

Post by NullifyNAN »

akiselev wrote: post #47

Is it just me, or did this article dance around the question? I am not a physicist but let me give it a stab: except for a few specialized steps like UV or oxidizing heavy metals, most filtration is mechanical. A series of filters with smaller and smaller pores capture more and more of the mess in the water like bacteria and particulates while UV breaks down viruses, the oxidizer precipitates out metals, and so on. N…

One minor thing is that the polyamide membranes that are used are more based on hydrogen bonding capability than pure porosity.

Basically the water can hydrogen bond with the polyamide but the salt can not and is therefore left behind.

Re: Why is desalination so difficult?

#305

Post by ftxbro »

throw0101a wrote: post #300
johnwalkr wrote: post #285

Earlier quoted context omitted.

Not Canadian maple syrup, it's regulated. I am pretty sure the regulations started from the producers getting together, or at least has the full support of the producers to keep up quality/reputation.

> Not Canadian maple syrup, it's regulated. Correct for things with that specific label, but other X syrup labels can be fair game: > In the United States, table syrups can be sold under a name consisting of any word followed by the word syrup with the exception of maple, cane, and sorghum. Commonly used names are table syrup, pancake syrup, waffle syrup, and pancake and waffle syrup.[1] * https://en.wikipedia.org/wi…

I assume that any syrup without a listed maple syrup grade is corn syrup.

Re: Why is desalination so difficult?

#306

Post by JshWright »

MarkusWandel wrote: post #301
giantrobot wrote: post #256

Earlier quoted context omitted.

Part of the flavor of maple syrup is due to caramelization and the Maillard reaction of components of the sap. Just concentrating the sap would get you a syrupy substance sourced from a maple tree but it wouldn't be maple syrup .

I've never liked the flavour of maple syrup very much. At the same maple syrup place visit, we had some, on pancakes. WTF? This is plain table sugar! What kind of stunt are you pulling here? The guy supervising the boil said don't you know? The very best grade is like that, hardly maple-y at all! Turns out it really was about the sugar all along, with the initially undesirable maple flavour coming to be prized over t…

The stronger colors and flavors occur later in the season. The warmer weather allows more bacteria growth in the sap, which metabolizes some of the sugar into other compounds.

Re: Why is desalination so difficult?

#307

Post by frumper »

r3trohack3r wrote: post #295
bsder wrote: post #165

Earlier quoted context omitted.

Agreed. Desalinization is cheap. It works just fine for providing water for coastal people . As California is proving. What it does not do is provide freshwater for argibusinesses. As California is also proving in the Central Valley. :(

From my (limited) understanding of agribusiness, particularly in California, it will be hard to be cost competitive with current water sources moving forward as they are heavily subsidized (read: near-zero costs). The upfront cost from my understanding is in drilling a deep well. Those wells keep getting deeper and costing more. But, past that, it's just the cost of running the pumps to drain the underground aquifers…

Pumping is at cost to them, but irrigating they pay a whole $20 per acre foot from our local water district. The wells are used when they want more than allotted.

Many of these canals are quite old and while they do require some maintenance, the upfront costs of the dams, reservoirs , and canals are largely paid off. Those maintenance costs and any upgrades are paid by the district customers.

Re: Why is desalination so difficult?

#309

Post by luhn »

ftxbro wrote: post #253
MarkusWandel wrote: post #12

Some years ago I toured a maple syrup operation that has the opposite goal: Concentrate the dissolved stuff in the water. Their first stage was reverse osmosis, but only to a point. Second stage is boil, but with aggressive heat recovery from the steam to preheat the incoming liquid. All this to keep the energy cost under control.

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.

Re: Why is desalination so difficult?

#310

Post by myshpa »

fsckboy wrote: post #293
mschuster91 wrote: post #252

Earlier quoted context omitted.

The problem is that salt brine from seawater contains a lot of side stuff - you still need purification at a scale you don't need mining rock salt.

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

Microplastic pollution in commercial salt for human consumption: A review [2019]

https://www.researchgate.net/publication/331006661_Microplas...

"MPs have been found in commercial salts from 128 brands, from 38 different countries spanning over five continents."

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