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The Dirty Truth About Turning Seawater into Drinking Water

earther.gizmodo.com

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Re: The Dirty Truth About Turning Seawater into Drinking Water

#121

Post by darkpuma »

eitland wrote: post #112
kiriakasis wrote: post #50

Earlier quoted context omitted.

Actual question, how many time can air be breathed? I think you can live on second-hand breath.

Can't answer the question, but I can say that when I did HUET we'd breathe into a bag in the suit and back again. This worked surprisingly well for the time we needed to stay underwater before we could escape. I'd still warn against implementing ones own version of this without studying the topic well, there's a number of pitfalls that one might not be obvious of up front. I've briefly considered if there might be so…

Chemically scrubbing the CO2 from exhaled air so it can be breathed again is the principle rebreathers work on.

Re: The Dirty Truth About Turning Seawater into Drinking Water

#122

Post by scotty79 »

ryanmercer wrote: post #117
scotty79 wrote: post #71

Earlier quoted context omitted.

Still we are talking about ingesting few microscopic particles per day. If they were cyanide it might have been harmful but they are mostly inert undigestible polymer with possibly traces of some additive if they surivived all previous stages of plastics life. Like floating in saltwater for few years or perhaps even already being in digestive systems of some aninals. I wouldn't bother with microplastics in salt. Not…

>Still we are talking about ingesting few microscopic particles per day. Which is going to increase. Plastic plumbing, plastic containers, plastic clothes, plastic cooking surfaces, plastic in the water, plastic in the salt, plastic in the air, plastic toothbrush bristles, plastic microbeads in body scrubs etc. Most plastics are effectively forever, they break down into smaller and smaller pieces creating the micropl…

I'm just saying there are bigger concerns right now. Such as air quality.

Re: The Dirty Truth About Turning Seawater into Drinking Water

#124

Post by kijin »

lifeformed wrote: post #93
saagarjha wrote: post #70

Earlier quoted context omitted.

> Also, I am not an expert.. but, couldn't we use the leftover salt for energy storage? I don't think salt is something that is in particularly short supply.

But wouldn't having it in a stable form as a mountain of salt be a decent storage solution? Or would the volumes produced be quickly untenable?

The mountain of salt will have a mass of at least 3.5% of the total amount of water you produce. It will be a lot more than that if you only use some of the water and let the rest evaporate.

For example, Israel produces more than 1 million tonnes of fresh water per day. That's 35,000 tonnes of salt, or 16,000 cubic meters -- enough to cover a football field to a depth of 3 meters -- every single day.

Re: The Dirty Truth About Turning Seawater into Drinking Water

#125

Post by kbutler »

mcv wrote: post #58

I admit I had not expected this to be a problem. The salt water comes from the sea, I'd expected it to be fine to release the salt back into the sea. But I understand that untreated, this extra-salty water would, in large amounts, become a current of its own that's significantly different from regular sea water. And apparently there are added chemicals in it that I suppose were necessary for the desalination process?…

There are no extra chemicals - the brine is just concentrated sea water. The chemicals are present in sea water, they've just been concentrated by removal of 40% of the water.

Re: The Dirty Truth About Turning Seawater into Drinking Water

#126

Post by kup0 »

semi-extrinsic wrote: post #97
freeflight wrote: post #87

Earlier quoted context omitted.

> Also, producing more brine would make the brine less concentrated and less harmful - it would be better not worse. Producing more brine, by diluting it, still would require something to dilute it with. The most obvious, non toxic, choice would probably be water, but the whole exercise is about getting water in the first place.

You can just dilute with seawater, as discussed elsewhere in this thread.

Does diluting it with seawater (after which I assume it is returned to the sea?) result in an endlessly increasing salt level in the seawater, over a long period of time, that will reach a dangerous level at some point?

Edit: I realize my naivety now. Other comments mentioned the desalinated water (at least some of it) will end up back in the sea eventually, so that would maybe counterbalance such a concern.

Re: The Dirty Truth About Turning Seawater into Drinking Water

#127

Post by manicdee »

kup0 wrote: post #126
semi-extrinsic wrote: post #97

Earlier quoted context omitted.

You can just dilute with seawater, as discussed elsewhere in this thread.

Does diluting it with seawater (after which I assume it is returned to the sea?) result in an endlessly increasing salt level in the seawater, over a long period of time, that will reach a dangerous level at some point? Edit: I realize my naivety now. Other comments mentioned the desalinated water (at least some of it) will end up back in the sea eventually, so that would maybe counterbalance such a concern.

The short term effects are increased salinity and reduced oxygenation for water in the immediate vicinity of the desalination plant, which is enough to drastically alter the biome (aka “kill all the sea life”).

Re: The Dirty Truth About Turning Seawater into Drinking Water

#128

Post by manicdee »

tim333 wrote: post #94
arkades wrote: post #6

Just to be clear, "brine" isn't "salty water." > This untreated salt water can’t just hang around in ponds—or, in worst-case scenarios, go into oceans or sewers. Disposal depends on geography, but typically the waste does go into oceans or sewers, if not injected into wells or kept in evaporation ponds. The high concentrations of salt, as well as chemicals like copper and chlorine, can make it toxic to marine life. >…

The dictionary definition of brine is "water strongly impregnated with salt." ie salty water.

No. You can’t take the dictionary definition, ignore the important word, then claim two things are equal.

Salty water is not water strongly impregnated with salt.

To simplify, the difference between salty water and brine is that brine is very salty water. The concentration of salt completely changes the environmental impact. Dumping post-desalination brine back into the ocean is an environmental disaster.

Re: The Dirty Truth About Turning Seawater into Drinking Water

#129

Post by Gibbon1 »

nabla9 wrote: post #74

This is not a show stopper. If you discharge brine into the sea, you should have to have a plan to dilute and mix brine. High concentration brine does not automatically mix into the sea water. The underflow goes into the bottom of the sea and forms a separate layer. But you can use nozzle diffusers, mixer etc. and discharge into high currents.

In Southern California I think the plans are to mix the brine discharge with the treated sewage outflow.

Re: The Dirty Truth About Turning Seawater into Drinking Water

#130

Post by D_Alex »

tda wrote: post #114
D_Alex wrote: post #86

Earlier quoted context omitted.

Simple math will tell you that this increase cannot be due to desalination. Look: Volume of the Persian Gulf = Area (251,000 sq km) * average depth (50 m) = 12,000 cubic km approx. Total amount of desalinated water produced in the world, per annum = 86 million cu. m = 0.086 cu. km, So if all of the world's desalinated water was taken from the Persian Gulf, for 150 years, the salinity would only increase by 0.08*150/1…

Always good to do some math. I double checked your input figure, and that should be per day, not per year. So 365 times as high. Other assumptions being the same that would give 0.2% rise per year, or 4% in twenty years. Not 50%, but not insignificant.

You are right, thanks for pointing this out. I hate making mistakes like that.
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