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From seawater to drinking water, with the push of a button

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Re: From seawater to drinking water, with the push of a button

#21

Post by MichaelApproved »

fiddlerwoaroof wrote: post #11
MichaelApproved wrote: post #9

Earlier quoted context omitted.

“ Atmospheric Water Generators ” At first I thought you were just using a marketing term for dehumidifiers but I looked it up before posting. I see that term is used for tight mesh fabric that’s hung vertically as a passive matrix to collect condensation. While those are actually game changers, they unfortunately only work in special regions that have the needed weather and topography to make them work. I think there…

I wonder if you could use a similar sort of device with weather balloons to harvest water from clouds.

Would dry regions that need water have enough cloud coverage for that to be viable?

My guess is that any place with sufficient cloud coverage is already getting enough rain water to satisfy their needs.

Re: From seawater to drinking water, with the push of a button

#22

Post by dehrmann »

> The suitcase-sized device...can also be driven by a small, portable solar panel,

> Yoon and Kang used machine learning to find the ideal combination of ICP and electrodialysis modules.

These bits feel like they were added because ML and solar power will get more clicks.

Re: From seawater to drinking water, with the push of a button

#23

Post by nullc »

MichaelApproved wrote: post #19
QuikAccount wrote: post #15

Earlier quoted context omitted.

You can pump brine water back but if I recall you can't just dump it all back at once because it's so highly concentrated. Ideally you would be able to find an alternate use for it.

For these small amounts, I doubt pumping it back out would be an issue but is that what they’re doing? I thought the metal plates were collecting the salt but the article and video don’t make it clear.

In CEDI at least the ions are trapped in a resin then are driven across a membrane by a charge, on the other side of the membrane you run water to flush them out.

Some comment in the article left me thinking they end up trapping them in the media and have to reverse charge to release them so I assume it would operate pulsed and presumably have a valve to dump the output during regen.

Though I'm a little confused in that normally CEDI is used after RO because the CEDI media is pretty sensitive to fouling and also doesn't work well when the water conductivity is highly variable. Maybe they solve the fouling with charge reversal.

...who knows, because popular coverage of this stuff never hits on the important parts and almost never links the relevant publications. There are many ways to make drinkable water from seawater-- making them some useful mixture of energy efficient, cost effective, portable, waste-water efficient, and reliable is the actual hard part.

Re: From seawater to drinking water, with the push of a button

#24

Post by dfsdf4sds »

MichaelApproved wrote: post #6

Edit: I wrote out the comment below criticizing the efficiency of this device, when compared to reverse osmosis RO desalination (100x less efficient). However, they’re not trying to be more efficient than RO devices, they’re trying to be more compact, portable, and avoid the need for filters. They’re solving for a different problem than I was measuring them against. In my race to criticize, I overlooked those key det…

I want to thank you for your edit, and for keeping the original text. Recognizing something you said ignored portions of the argument, changing the argument, and keeping the original portion to show _why_ you were wrong but still adds to the conversation is very valuable. I commend you for your ability to double guess yourself

Re: From seawater to drinking water, with the push of a button

#26

Post by fiddlerwoaroof »

MichaelApproved wrote: post #21
fiddlerwoaroof wrote: post #11

Earlier quoted context omitted.

I wonder if you could use a similar sort of device with weather balloons to harvest water from clouds.

Would dry regions that need water have enough cloud coverage for that to be viable? My guess is that any place with sufficient cloud coverage is already getting enough rain water to satisfy their needs.

I think there are parts of coastal California where there are clouds more of the year than rainfall. I'd also suspect if you just raised them up with balloons to cool them off and then brought them down where it's warmer, you could condense evaporation from the ocean, without spending energy directly on cooling.

Re: From seawater to drinking water, with the push of a button

#27

Post by electroly »

MichaelApproved wrote: post #18
electroly wrote: post #13

Earlier quoted context omitted.

FWIW, I think you made a minor math error; you lost track of the 30 minutes. It would be 1 ounce of water for 3 watts of power over 30 minutes , which is 1.5 Wh of energy. That's 666 ounces per kWh.

It wouldn’t be the first time I made a mistake like that by not clearly identifying my units but I think I got it right. Let me rephrase and use watt/hour units. I was assuming it was a 50 watt panel that would only produce 30wh from the weak winter sunlight. Divide 30wh by two (since it was only ru Ning for half an hour) and get 15 watts generated to purify 5 ounces. Had they let it run for the full hour, they’d get…

Wh is a measurement of energy, but W is a measurement of power (that is, the rate of energy). They are different units of measurement and you're mixing them up here. Here, you've doubled the original rating of 15 watts up to 30 watts; that's the result of the confusion between energy and power. You don't divide the wattage in half when you run it for half the time, nor double it when you run it for twice the time; that's not how power works. That's how energy works.

In your original post, the number was 15 watts, and you figured it produced 5 ounces of water in 30 minutes. So you then figured that 3 watts can produce 1 ounce of water in 30 minutes. So far so good; that's correct. If the panel continuously produces 3 watts of power (remember: watts are a rate of energy) over a period of one hour, that's 3 watt-hours of energy. For 30 minutes, it's 1.5 watt-hours of energy. Thus, it took 1.5 watt-hours of energy to produce 1 ounce of water. (1000 watt-hours) * (1 ounce / 1.5 watt-hours) = 666 ounces.

It may make more sense to translate this into distance, which I think is more intuitive for most people. Watts (power) are like miles-per-hour (velocity), and watt-hours (energy) are like miles (position). The panel runs at 15 MPH. After 30 minutes it has run 7.5 miles and produced 5 ounces of water. Thus, it could produce 1 ounce of water by running just 1.5 miles. It still runs at a speed of 15 MPH no matter what.

Re: From seawater to drinking water, with the push of a button

#28

Post by kylehotchkiss »

Southern California is beginning to see more water restrictions - each and every desalination tech advancement is a very hopeful development for the region, and many others in the world that can't get enough freshwater. I hope they can generally work this up to factory scale and put it behind a solar farm and see if that can supply a lot of homes.

Re: From seawater to drinking water, with the push of a button

#29

Post by KennyBlanken »

If I had a dollar for every project MIT's press office has said will be revolutionary and end (insert major world health/water/resource/energy/food problem), I'd be a very, very rich person.

I'm not sure why MIT's press office gets so much favor here, particularly given their/MIT's track record.

Post articles by science journals and news outlets that will tell us if this is actually going to work or if it's just yet another go-nowhere project.

Re: From seawater to drinking water, with the push of a button

#30

Post by KennyBlanken »

kylehotchkiss wrote: post #28

Southern California is beginning to see more water restrictions - each and every desalination tech advancement is a very hopeful development for the region, and many others in the world that can't get enough freshwater. I hope they can generally work this up to factory scale and put it behind a solar farm and see if that can supply a lot of homes.

The problem is that southern California is trying to grow a shit-ton of crops that aren't suitable for the environment there. The almond industry is particularly guilty in this regard.

Desalination will never scale to a level suitable to supply that industry. If anything they'll take that water and just grow even more crops, while still sucking the aquifer dry.

Thing is, aquifers compact when you draw water from them too much. That compaction can never be undone. They are slowly rendering that land permanently uninhabitable.

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