Why is desalination so difficult? • Hacker News Board

Re: Why is desalination so difficult?

#191

Post by justinator » Wed, Jul 05, 2023, 8:14 PM UTC

cratermoon wrote: post #105

LordDragonfang wrote: post #76

Earlier quoted context omitted.

I mean, that's actually not too much of a downside, since salt is a fairly valuable economic good - Indian salt farmers do exactly that to harvest the salt crystals.

Destroying existing ecosystems is kind of part of how we got where we are now.

We're coming to the inevitable conclusion that we can't keep doing this, as there's little existing ecosystems to destroy - I mean: we're looking at deserts and thinking: "why not?". Slightly more outlandish, we're looking at whole planets and thinking the same.

Some call that par for the course, others unsustainable. Still others don't make a distinction and see them as the same.

Re: Why is desalination so difficult?

#192

Post by mcculley » Wed, Jul 05, 2023, 8:14 PM UTC

luxuryballs wrote: post #35

Can I shower in salt water? Then all I need to do is desalinate drinking water. “Distributed” home desalination for drinking water seems like the best approach in my mind, then people can pay as much or as little they need, but I have no real data to back this up.

Yes, I do this on boats quite often. It is unpleasant compared to showering with fresh water.

Re: Why is desalination so difficult?

#193

Post by jhoechtl » Wed, Jul 05, 2023, 8:16 PM UTC

lisper wrote: post #154

darkclouds wrote: post #142

Earlier quoted context omitted.

Its always been my understanding that any treatment to remove stuff from water is going to produce waste which needs disposing, just look at the Brita water jug filters, they need disposing. I've often wondered why dont we have more pure water pumped through the water mains in various countries, and I think after reading about Super K the Japanese Neutrino detector [1] and how the water in the tank was so pure it had…

> the water in the tank was so pure it had dissolved a spanner/wrench that was left in the bottom "Apparently somebody had left a wrench there when they filled it in 1995," he said. "When they drained it in 2000 the wrench had dissolved." I dunno, I think if you left a wrench soaking in regular water for five years there wouldn't be much left of it after that either.

> I dunno

During WWII Entire tanks drowned in Siberian sumps and were brought back to life with their engines running.

After five years in regular water I bet the wrench would be in working condition.

Re: Why is desalination so difficult?

#194

Post by bjelkeman-again » Wed, Jul 05, 2023, 8:17 PM UTC

jerf wrote: post #126

tivert wrote: post #119

Earlier quoted context omitted.

> 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? Too much salt can kill stuff (e.g. people, plants), so I suppose that makes it "toxic." May…

There are several practical problems dumping the brine back in the sea. If you dump it on a living ecosystem you tend to kill it. Living ecosystems are, unfortunately, concentrated right where we are desalinating and is cheap to dump. Compounding this problem is that water mixes much more slowly than your intuition suggests. It can stay a coherent mass of high-salt water way longer than you'd think, killing as it goe…

The extreme volumes produced in the Arabian Gulf is subject to a lot of studies (some plants produce one million m2 per day). This does cause issues. An in-depth look at possible futures can be found here.

http://essay.utwente.nl/79579/1/Dols%2C%20F.J.%201862227%20_...

Re: Why is desalination so difficult?

#195

Post by stOneskull » Wed, Jul 05, 2023, 8:21 PM UTC

jakear wrote: post #98

luxuryballs wrote: post #62

Earlier quoted context omitted.

yeah but I usually feel quite refreshed after coming out of the waves, but keep in mind we don’t need clean feelings to survive, we do need fresh drinking water

Salt overexposure is liable to dry up your skin and cause rashes/cracking leading to vectors for infection.

you see that with surfers. at 30, they look like they're 50

Re: Why is desalination so difficult?

#196

Post by agnosticmantis » Wed, Jul 05, 2023, 8:30 PM UTC

Given the countless environmental challenges we are facing (and causing), we should more seriously and openly consider putting a stop to exponential population growth as an (at least short-term) solution. It’s astonishing how some people preach blind faith in our ability to just find solutions for problems caused and exacerbated by never-ending population growth without identifying it as the root cause. Why is it a given that the earth can just withstand whatever we throw at it?

Re: Why is desalination so difficult?

#197

Post by WJW » Wed, Jul 05, 2023, 8:32 PM UTC

11101010001100 wrote: post #177

tshaddox wrote: post #22

Earlier quoted context omitted.

Right, but that’s easy. If desalination only required lifting each unit of water a few inches we probably wouldn’t say it’s particularly difficult.

Easy as in moving mass against a gravitational potential? Didn't know building a rocket was easy.

Moving water against a gravitational potential has been done for literal millennia and no rocketry is required. A water pump will suffice.

Re: Why is desalination so difficult?

#198

Post by Retric » Wed, Jul 05, 2023, 8:44 PM UTC

suddenclarity wrote: post #145

stouset wrote: post #128

Earlier quoted context omitted.

If people needed as much salt as was contained in the water to begin with, we wouldn’t need to remove it in the first place.

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 waste stream doesn’t contain that much more salt than seawater. Extracting salt from mines is much cheaper than extracting it from slightly brackish wastewater from water treatment plants.

Re: Why is desalination so difficult?

#199

Post by Robotbeat » Wed, Jul 05, 2023, 8:45 PM UTC

rtkwe wrote: post #168

xenadu02 wrote: post #110

Earlier quoted context omitted.

No, fresh water just enters the water cycle. It will eventually evaporate or end up in a river and back into the ocean where it will be reunited with the salt. The overall salt concentration of the ocean would not be changed unless we sequestered the fresh water permanently. Even then it would take a tremendous effort to make even the tiniest difference in salinity.

It will change the salinity on the short term though at the release location and the amount a large plant will be discharging is enough to alter the local salinity so long as the plant remains operational which will negatively affect sea life in that area.

Only if the discharge is not diluted sufficiently.

There is nothing about reverse osmosis that is fundamentally more toxic or harmful than the typical evaporation that takes place naturally in the ocean. And it’s pretty dishonest to claim otherwise. If there’s a problem with too high salinity of discharge, that’s an engineering problem that should be fixed with greater dilution.

Re: Why is desalination so difficult?

#200

Post by Robotbeat » Wed, Jul 05, 2023, 8:49 PM UTC

jerf wrote: post #126

tivert wrote: post #119

Earlier quoted context omitted.

> 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? Too much salt can kill stuff (e.g. people, plants), so I suppose that makes it "toxic." May…

There are several practical problems dumping the brine back in the sea. If you dump it on a living ecosystem you tend to kill it. Living ecosystems are, unfortunately, concentrated right where we are desalinating and is cheap to dump. Compounding this problem is that water mixes much more slowly than your intuition suggests. It can stay a coherent mass of high-salt water way longer than you'd think, killing as it goe…

> If you dump it on a living ecosystem you tend to kill it.

This is false and somewhat dishonest. This is simply a choice of not diluting it enough. There is nothing about the discharge from reverse osmosis that is any more fundamentally toxic than the natural process of evaporation.

Proper dilution is essential, and treating the discharge as fundamentally toxic actually undermines the engineering to do this proper dilution because people will figure “oh well, I guess there’s nothing we can do as it’s going to tend to kill no matter what.”

People need to stop misleading about discharge toxicity.