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Comment by AYBABTME | Hacker News Reader

The concern over brine is something I'm willing to contemplate but on the face of it, it seems to me that brine would only be a problem in the immediate zone where it is returned.

And then again the fresh water produced along with the brine will end up back in mostly the same surrounding after it gets used, so it's not like we're producing saltier and saltier water over time?

So aside from the increased salinity at the specific location where the brine is returned to the sea, is there another issue? Am I missing something that makes all this a large scale problem?

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Not necessarily a “large scale” problem but the increased salinity means you create a enormous dead zone near your output system unless you spend a ton of energy to mitigate it.

We had Bechtel design us a desalination/RO system for a biofuel startup I worked with and to prevent the dead zone, you need a massive system of buried pipes in the ocean. Iirc, it was the most expensive part of the entire design since you need to output it over something like a square kilometer and you need to mix in fresh seawater at several points to dilute the effluent before you release it. So in addition to the CapEx of a construction project in a horribly hostile environment, you have permanent energy consumption even past the filters.

And of course, since it’s coastal, there are tons of regulations and government bodies interested in making sure you don’t cut corners.

There must be some creative solutions to the brine problem. At the end of the day we’re really not processing much seawater compared to the size of the ocean.

Right but the size of the ocean is the wrong metric - it’s really only the coastal region adjacent to the desal plant that you have to work with, and the chemistry and power realities mean that you just have a ton of very salty water to pump through pipes.

Put the lithium plant on a barge and tug it around without lingering too long in any one spot.

Awesome idea! Or even build on a platform and locate in a major current like the Gulf Stream. That could mix it pretty fast.

Wouldnt a platform to hold a factory be more expensive than a few km of pipes?

Not just a factory, but the primary issue with desal is that it takes a ton of energy, so you’d also need a power plant…

I wonder if one could not simply pump it into some old oil reservoirs. The nations that need to do seawater refining should have some nearly empty oilfields lying around.

Salt water intrusion into the aquifer is pretty bad for agriculture. Not sure if that would be a problem with refilling oil reservoirs but I'm not an expert.

Interesting answer and thanks for providing it. Do you think the geography of the coast changes how expensive this gets? I'd think a coast that goes deep quickly or has strong currents wouldn't need as much spread out disposal infrastructure as one in a shallow area.

Yeah it 100% does - mixing rate is a big design driver. We actually had decided that is was better for our primary effluent pipe to be several KM longer to reach the “coast” vs the smaller bay that we were immediately adjacent to.

But even then, if the ends of your system are in 50’ deep ocean, the water column is such that the top ~10% sees really good mixing and exchange due to wind and wave action but the rest really doesn’t. It’s rare that there are strong currents near enough coastlines to take advantage of.

Wow, most people never consider the dead-zone around desalination plants. Us landlubbers just think of it as manna from heaven, “free freshwater.”

The way we discuss technical solutions is woefully inadequate. Everything is still presented as a miracle-cure for our problems. We should have a more mature understanding of how these things are constructed and maintained.

The ocean is pretty big. That's why fish poop and pee in it. Not much of a problem. And if you weren't already aware, did you know plants also excrete waste through their roots? I only found out recently. But yes, all waste needs to be spread out and able to diffuse into the large atmosphere or it causes dead zones.

Yes.

One piece of poop in the forest—nature.

A sewer pipe discharging a river of poop from an entire city into a forest—a toxic waste dump.

The entire surface of the sea is evaporating fresh water and the resulting brine is slinging constantly. It’s not creating a dead zone because it’s distributed. A river of brine in the oceans would be like a toxic cloud of ammonia that kills anything it touches…until it mixes sufficiently.

Which was my point. As long as the outtake is distributed, it would be fine. I think everyone is aware of that..even the landlubbers..

We kind of figured it out 150+ years ago:

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

Plant wastes are a part of an eco system. They are cunsomed and transformed into other wastes. Actually, only human beings see wastes as a definitive lost. For every sustainable cycles, a waste is going to be transformed into you will consume again.

The brine problem is played up because environmentalists don’t like building new industry to solve environmental problems. A big part of their psyche is that man must suffer for his sins against nature. IMO.

No, environmentalists simply say that it’s worth to preserve the environment that humanity evolved in. One reason is for our grandchildren to be able to experience it and another is we don’t really know what happens if we destroy too much of it - we do have localized examples though and they’re really not good.

Environmentalists are mostly political today, they focus their efforts on benign & wealthy countries instead of the most polluting. (Which are often poor or run by dictatorships)

I, too, focus on problems at home that I have any hope of changing rather than yelling at countries on the other side of the planet that have zero incentive to listen to me.

Are you suggesting no country should tell any other country how to be environmentally conscience?

I would argue that those countries that are cleaner have the moral authority to lead the way to a cleaner planet.

I'm suggesting it is bullshit to disparage environmentalists just because theyre focused on problems in their local country.

Countries should totally put pressure on others, but individual environmentalists putting pressure on their local countries makes sense.

the US, by virtue of having guns pointed at the leaders of every other country, should be telling every other country to be environmentally conscious.

Unfortunately, the US itself needs to beinfluenced into being environmentally conscious

of course they're political, how else do you get to change policies? chaining yourself to trees doesn't do much nowadays.

The environment. Yes or no?

Candidate 1: No. It's junk science.

Candidate 2: Two words: Condor attack. Don't want that. Got to say no.

...

Candidate 5: Enviro-mite!

This brine argument makes no sense - they are extracting lithium - you can pump everything else back if you want

> fresh water produced along

Oh, if they are producing fresh water as well then isn't this good as desalination is already needed in some area's. So the studies upon the brine they output would be useful to measure any impact. Which would be localised - how localised and impacting is really the question here and for that we can look at existing drinking water from sea water production.

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