Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Why is desalination so difficult?

practical.engineering

Post reply on HN
Print view View original

281–290 of 644 posts

Re: Why is desalination so difficult?

#281

Post by kortilla »

caseyohara wrote: post #92
qorrect wrote: post #51

Earlier quoted context omitted.

[flagged]

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.

Yes, but you picked the the most interesting desert. Doing this to one particular area that is already ruined (the salton sea) in a desert with far less wildlife is worth discussing.

Re: Why is desalination so difficult?

#282

Post by rs999gti »

giantrobot wrote: post #220
suddenclarity wrote: post #145

Earlier quoted context omitted.

No reason to keep the 1:1 ratio. Use the salt to replace our current salt mines/outtakes and then use the water as an addition to our current freshwater usage.

The brine waste from RO is still mostly water. In order to extract the salt you'd need to evaporate the water which still takes a lot more energy. You could use evaporative ponds to let the Sun do the work but that takes a lot of space. In either case you're spending a lot more money per pound than just digging the salt out of a mine.

> https://www.bbc.com/news/business-61483491

Nuclear desalination like on naval ships is the answer. US and Russian ships already have the technology, it just needs to be scaled for use on land.

Re: Why is desalination so difficult?

#283

Post by no_wizard »

ramesh31 wrote: post #70
nerbert wrote: post #34

Earlier quoted context omitted.

In 2022, 85% of the country's drinkable water was produced through desalination of saltwater and brackish water. If there is a real need, and a will to address it, we have everything we need to to it. https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in...

>In 2022, 85% of the country's drinkable water was produced through desalination of saltwater and brackish water. Israel does this by burning massive quantities of fossil fuels: https://en.wikipedia.org/wiki/Energy_in_Israel#/media/File:E... It's not even remotely economical without huge government subsidies. Completely untenable with current technology for poorer countries, or anyone that cares at all about carbon e…

Nuclear energy has entered the chat

Why not use nuclear power plants to power desalination plants? I even wonder if some of the salt from the brine could be fed into certain types of nuclear reactors (Molten Salt Reactors and the like, possibly) making it an even more symbiotic relationship

Re: Why is desalination so difficult?

#284

Post by mr_toad »

dfxm12 wrote: post #89
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…

It takes less energy but produces a concentrated liquid waste stream that must be disposed of. I've heard that this brine is toxic. Does this make disposal an issue? Is the toxicity true or hyperbole? I mean, do we know how bad it is, and if we can do anything safely with it? It seems like "salt" is useful in a lot of contexts, including industrial, so can we do something with the brine besides disposing it somewhere…

Even normal seawater has toxic concentrations of salt:

“seawater's sodium concentration is above the kidney's maximum concentrating ability. Eventually the blood's sodium concentration rises to toxic levels, removing water from cells and interfering with nerve conduction, ultimately producing a fatal seizure and cardiac arrhythmia.”

https://en.wikipedia.org/wiki/Salt_poisoning

Re: Why is desalination so difficult?

#285

Post by johnwalkr »

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?

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.

Re: Why is desalination so difficult?

#286

Post by anamexis »

no_wizard wrote: post #283
ramesh31 wrote: post #70

Earlier quoted context omitted.

>In 2022, 85% of the country's drinkable water was produced through desalination of saltwater and brackish water. Israel does this by burning massive quantities of fossil fuels: https://en.wikipedia.org/wiki/Energy_in_Israel#/media/File:E... It's not even remotely economical without huge government subsidies. Completely untenable with current technology for poorer countries, or anyone that cares at all about carbon e…

Nuclear energy has entered the chat Why not use nuclear power plants to power desalination plants? I even wonder if some of the salt from the brine could be fed into certain types of nuclear reactors (Molten Salt Reactors and the like, possibly) making it an even more symbiotic relationship

The OP brushes on this

Re: Why is desalination so difficult?

#287

Post by janalsncm »

tguvot wrote: post #138
jbm wrote: post #122

Earlier quoted context omitted.

I wasn't too clear about what I meant, but is storage even necessary here? For example, would there be an issue if the desalination process was left in an intermediate state for X hours / days while power is intermittent? I wonder if there are more energy-expensive desalinization processes that are better to use with intermittent power sources, like solar.

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.

Re: Why is desalination so difficult?

#288

Post by rs999gti »

bsder wrote: post #165
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…

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. :(

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?

Re: Why is desalination so difficult?

#289

Post by rs999gti »

stouset wrote: post #280
rs999gti wrote: post #278

Earlier quoted context omitted.

Can't the salt just be dumped in the desert?

The products of desalinization aren’t salt and fresh water. They’re somewhat saltier brine and fresh water.

Sounds like it's time for USA to get another Salton Sea

Re: Why is desalination so difficult?

#290

Post by pfdietz »

Veserv wrote: post #112
iudqnolq wrote: post #82

Earlier quoted context omitted.

*typical American household uses directly. Don't forget food, industrial, etc

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…

> 1550 cubic meters per year

This is an interesting number. Recently, I saw complaints that green hydrogen is impractical because it would use too much water. But if all the per capita energy use in the US went to electrolysis, it would use about 1% of this water per capita (and, of course, green hydrogen would be only a fraction of total energy use, due to all the preferred direct uses of electrical energy.)

Post reply on HN