We require 130 litres / person per day in Europe. A town of 10,000 people would require 1,300,000 litres / day = ~54,000 litres / hour = 9000 metres-squared.
A facility of 100 x 100 x 1 m seems feasible. Based on those calculations, this all seems quite practical. I do wonder how frequently the filters need to be changed, though.
If this desalination system allowed a city to generate even 50% of their water needs, that would be a significant step forward. I keep seeing this metric put forward: Does X generate 100% of the needed water/electricity/heat. Why does it have to 100%? Can't three systems each contributing 33.3% be enough to reach 100%?
Our household solar power installation here in the very rainy Seattle area generates 98.15% of our electric power needs, including that for our electric car. I wish it were 100%, and if the sun shines for a few days in a row, sometimes it does generate 100% of our electric power needs for the last 365 days. It is, however, much better to meet 98% of our needs that to meet none of our needs.
It's 6 liters per square meter of solar membrane. They increased it 25x with a Fresnel lens. From the paper:
> For NEMD experiments with solar concentration, a 25.4 × 25.4 cm Fresnel lens was used to concentrate sunlight on the membrane surface by a factor of 25. The unconcentrated and concentrated solar intensities at the NESMD module surface were 0.7 and 17.5 kW·m−2, respectively.
A facility of 500x500 m^2 would probably still be feasible.
The link is to the university news department, the actual paper is here:
I thought 130 litres/person was quiet high and probably included things like water to grow vegetables, but no, one shower is between 30 et 50 litres and each time you go to the bathroom, it's 10 litres of drinkable water.
Of course, I you have saltwater and no freshwater, you would probably use saltwater in your toilets, so that could reduce the daily usage of at least 20 litres. But then, if you consider agriculture and manufacturing, I guess that the number of 130litres/person would blow up completely.
Presumably you'd need to generate 1.3M liters off of only daylight hours, making it more like 130m*130m per 10K people.
Cairo has a population density of 18K people per km2, so this would mean covering 2% of the area. For contrast, streets and parking take up ~40% of most US cities.
Most of that 1.3M litres is presumably going to be within a 12 hour period, surely? Whether it’s for human use (drinking, washing, flushing) or agriculture.
I guess you can produce constantly and store - a quick search suggests that 1.3M litres would barely be known to a reservoir but you wouldn’t have to worry about the seasonality of rainfall.
> We require 130 litres / person
> per day in Europe
We don't require 130 litres of potable water though, which is what this produces. Salt water's fine for washing, brushing teeth, flushing toilets, washing hands, and so on.
We were each producing drinking water ... "We require" is probably a bit strong - LiveStrong says the average male needs 13 cups of water each day. If you add in the amount of water we use based on our life-style, then I can believe 130l.
The general problem with membrane-based desal methods is membrane fouling and lifetime.
I'm not sure that increasing the complexity of the membrane substrate itself is a positive step here, or that a complex heating mechanism offers significant wins.
The alternative of more traditional membrane reverse-osmosis processing focusing on cheap substrates, whilst provisioning power separately (conventional solar PV would be suitable, and could be located on-site or remotely) seems rather more tractable.
Solar desalination is not new. KKR invested $100b in SunDrop farms which uses solar desal that produces energy (steam) and water for greenhouses in the desert.
Solar desalination is not new ... I performed the same feat in the '70s during Boy Scout camp-outs in Virginia Beach (Fort Story) [0]. What is new is the level of efficiency!
Frequently I hear how persons stranded at sea or on a small island die of thirst, and I wonder if they could have used the evaporation method in conjunction with the sun or fire, and a cloth set above to capture the evaporated water.
METTC dependant, a 'solar still' could work. With the right vegetation and a plastic bag you could even collect transpiration. Off topic, but interesting nonetheless.
Dumb question: would it be possible to turn the desert green?
I'm imagining something done little-by-little, through farming and maybe public trusts. If this kind of technology were to continue to fall in cost, could we have farms and forests in the Sahara?
Desalinization is becoming better understood, as well as cheaper, but the biggest challenge is still what to do with the leftover salt. We can't pour it back into the ocean because it will kill everything. Hopefully someday we find a way to clean and safe way to dispose of salt.
> We can't pour it back into the ocean because it will kill everything.
That's simply false. The amount of water that would need to be permanently removed from the ocean in order to measurably increase the salinity would be astounding. Let alone the amount that would need to be permanently removed to kill anything.
If local salinity was a problem (which it isn't) there's an extremely easy solution: Simply pump more water, remove less salt from it. Dump it in over a wider area of shore. Let mixing take care of the rest.
Most desalinization processes don't produce "salt", but extract a certain amount of unsalted water from the in put, leaving behind more salty water. Typically reverse osmosis at best reaches 1:1, that means you need 2 units of input water and get one unit of desalinated water and one unit of salty water. For sea water desalination 1:1 is quite optimistic though. This salty water can be safely put back into the sea. With very large scale plants you might want to make sure that you don't release the salty water at a single very concentrated spot.
It's not really a significant problem. Blending it with heated cooling water from power plants or treated effluent from waste water plants are common means of brine disposal. Provided you spread out the disposal in areas with good flow, even releasing the brine directly would have minimal impact.
There's no reason why we couldn't ship it into the middle of a desert if for some reason it couldn't go back into the sea, it wouldn't go very far once it was dumped. Conveniently, the places that rely/will rely on desalination the most happen to be desert countries.
In general, perform reverse osmosis (RO) until the effluent brine is up to 70 g/kg salinity. Then pump it out onto a salt pan, let the rest of the water evaporate, and sell the evaporite.
Petrochem tech comes into play here, because in steam extraction of oil-sands, wastewater comes back up contaminated with silicates, and has to be treated before it can be reused. It turns out that similar processes can be used to further concentrate desalinator effluent above the 70 g/kg that regular RO tops out at, to about 130 g/kg. From there, any solar/thermal process equipment (i.e. flash distiller) can be made much smaller.
For reference, seawater is typically 35 g/kg, and the top stratum of the Dead Sea averages 315 g/kg (with significant fluctuation due to local weather history).
So Jordan and Israel can actually do RO on water from the Red Sea (40 g/kg), and pump the effluent to the Dead Sea. They don't have to worry about the hypersaline brine killing anything, because the Dead Sea is already dead (just like it says on the tin). And the pumping is easy, because the Dead Sea is below ocean level. A pair of siphoning aqueduct pipelines (40 g/kg and 70 g/kg) can supply a RO desalinator in every town from Aqaba to Potash City.
I wonder if there's a good use to which the highly-salinated solution (the "leftover salt") could be put. It's a stretch, but I vaguely recall something about storing excess solar energy thermally, in dense piles of molten salt...
An abundance of salt hardly sounds like an environmental issue. By that I mean it's not a gas that's going off into the atmosphere nor a liquid seeping anywhere (on its own)
Load salt on the huge cargo ships already crossing the oceans. Build machines that dump salt overboard slowly and continuously as the ships make their voyages.
The ships are probably full one direction (when traveling from countries that manufacture a lot) but relatively empty on the way back, so there's probably free space.
Let's not forget that solar cannot be used for anything critical where reliability is expected. It requires backup from a reliable source to be practical.
[+] [-] bencollier49|8 years ago|reply
We require 130 litres / person per day in Europe. A town of 10,000 people would require 1,300,000 litres / day = ~54,000 litres / hour = 9000 metres-squared.
A facility of 100 x 100 x 1 m seems feasible. Based on those calculations, this all seems quite practical. I do wonder how frequently the filters need to be changed, though.
[+] [-] ccalvert|8 years ago|reply
Our household solar power installation here in the very rainy Seattle area generates 98.15% of our electric power needs, including that for our electric car. I wish it were 100%, and if the sun shines for a few days in a row, sometimes it does generate 100% of our electric power needs for the last 365 days. It is, however, much better to meet 98% of our needs that to meet none of our needs.
[+] [-] LeifCarrotson|8 years ago|reply
> For NEMD experiments with solar concentration, a 25.4 × 25.4 cm Fresnel lens was used to concentrate sunlight on the membrane surface by a factor of 25. The unconcentrated and concentrated solar intensities at the NESMD module surface were 0.7 and 17.5 kW·m−2, respectively.
A facility of 500x500 m^2 would probably still be feasible.
The link is to the university news department, the actual paper is here:
http://www.pnas.org/content/early/2017/06/14/1701835114.full
or here in PDF format:
http://www.pnas.org/content/early/2017/06/14/1701835114.full...
[+] [-] Kayou|8 years ago|reply
Of course, I you have saltwater and no freshwater, you would probably use saltwater in your toilets, so that could reduce the daily usage of at least 20 litres. But then, if you consider agriculture and manufacturing, I guess that the number of 130litres/person would blow up completely.
[+] [-] ivankirigin|8 years ago|reply
Cairo has a population density of 18K people per km2, so this would mean covering 2% of the area. For contrast, streets and parking take up ~40% of most US cities.
[+] [-] tolien|8 years ago|reply
I guess you can produce constantly and store - a quick search suggests that 1.3M litres would barely be known to a reservoir but you wouldn’t have to worry about the seasonality of rainfall.
Yeah, seems feasible. Almost too good to be true…
[+] [-] peteretep|8 years ago|reply
[+] [-] torrent-of-ions|8 years ago|reply
[+] [-] smoyer|8 years ago|reply
[+] [-] ajarmst|8 years ago|reply
[+] [-] Qwertious|8 years ago|reply
This is the reverse - dispose of the residue, keep the water.
[+] [-] dredmorbius|8 years ago|reply
I'm not sure that increasing the complexity of the membrane substrate itself is a positive step here, or that a complex heating mechanism offers significant wins.
The alternative of more traditional membrane reverse-osmosis processing focusing on cheap substrates, whilst provisioning power separately (conventional solar PV would be suitable, and could be located on-site or remotely) seems rather more tractable.
[+] [-] msl09|8 years ago|reply
[+] [-] rdlecler1|8 years ago|reply
[+] [-] smoyer|8 years ago|reply
[0] https://en.wikipedia.org/wiki/Solar_still
[+] [-] sandl|8 years ago|reply
Source: https://agfundernews.com/how-private-equity-giant-kkr-and-su...
[+] [-] ogrisel|8 years ago|reply
[+] [-] SubiculumCode|8 years ago|reply
[+] [-] totallynotcool|8 years ago|reply
[1] https://en.m.wikipedia.org/wiki/Solar_still
[+] [-] malloryerik|8 years ago|reply
[+] [-] kbart|8 years ago|reply
[+] [-] Overtonwindow|8 years ago|reply
[+] [-] ori_b|8 years ago|reply
That's simply false. The amount of water that would need to be permanently removed from the ocean in order to measurably increase the salinity would be astounding. Let alone the amount that would need to be permanently removed to kill anything.
If local salinity was a problem (which it isn't) there's an extremely easy solution: Simply pump more water, remove less salt from it. Dump it in over a wider area of shore. Let mixing take care of the rest.
[+] [-] noonespecial|8 years ago|reply
Now that's a job for you to tell your kid's school class about on career day. A salt un-miner.
[+] [-] _ph_|8 years ago|reply
[+] [-] dubyah|8 years ago|reply
[+] [-] toomanybeersies|8 years ago|reply
That's what's happening to the fresh water after it's used, it goes back to the ocean. It's a closed cycle.
The scale of human water consumption to the volume of the sea is miniscule.
Global fresh water consumption is a fraction of a percent of the volume of the ocean ( https://www.wolframalpha.com/input/?i=((total+water+consumpt... )
There's no reason why we couldn't ship it into the middle of a desert if for some reason it couldn't go back into the sea, it wouldn't go very far once it was dumped. Conveniently, the places that rely/will rely on desalination the most happen to be desert countries.
[+] [-] logfromblammo|8 years ago|reply
Petrochem tech comes into play here, because in steam extraction of oil-sands, wastewater comes back up contaminated with silicates, and has to be treated before it can be reused. It turns out that similar processes can be used to further concentrate desalinator effluent above the 70 g/kg that regular RO tops out at, to about 130 g/kg. From there, any solar/thermal process equipment (i.e. flash distiller) can be made much smaller.
For reference, seawater is typically 35 g/kg, and the top stratum of the Dead Sea averages 315 g/kg (with significant fluctuation due to local weather history).
So Jordan and Israel can actually do RO on water from the Red Sea (40 g/kg), and pump the effluent to the Dead Sea. They don't have to worry about the hypersaline brine killing anything, because the Dead Sea is already dead (just like it says on the tin). And the pumping is easy, because the Dead Sea is below ocean level. A pair of siphoning aqueduct pipelines (40 g/kg and 70 g/kg) can supply a RO desalinator in every town from Aqaba to Potash City.
[+] [-] Overtonwindow|8 years ago|reply
[+] [-] chrisweekly|8 years ago|reply
[+] [-] ianai|8 years ago|reply
[+] [-] unknown|8 years ago|reply
[deleted]
[+] [-] Cthulhu_|8 years ago|reply
[+] [-] adrianmonk|8 years ago|reply
The ships are probably full one direction (when traveling from countries that manufacture a lot) but relatively empty on the way back, so there's probably free space.
[+] [-] anotherbrownguy|8 years ago|reply
[+] [-] regularfry|8 years ago|reply