Freshwater from salt water using only solar energy(news.rice.edu)
news.rice.edu
Freshwater from salt water using only solar energy
http://news.rice.edu/2017/06/19/freshwater-from-salt-water-using-only-solar-energy-2/
107 comments
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.
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.
To hit that rate you need energy storage at your house, right?
In the context of grid power, that's an even bigger issue given cost and pollution from base load generators.
In the context of grid power, that's an even bigger issue given cost and pollution from base load generators.
Or three systems capable of producing more than 50%.
Because infrastructure should have redundancy.
Because infrastructure should have redundancy.
Five systems generating 33.3%, then. He's got a very valid point.
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.
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.
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.
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.
Maybe people can also shower with saltwater followed by a quick rinse in drinkable water. That would reduce the usage drastically.
I couldn't find anything against showering with saltwater by skimming the results of a naive google search.
I couldn't find anything against showering with saltwater by skimming the results of a naive google search.
You can get about the same effect by running the water to get wet, turning it off while washing and then back on for rinsing (the infamous "navy shower").
I imagine the biggest strike against showering with salt water is that you'd need treatment, supply and heating dedicated to the salt tap. And then the salt water is busy corroding all the infrastructure devoted to it.
I imagine the biggest strike against showering with salt water is that you'd need treatment, supply and heating dedicated to the salt tap. And then the salt water is busy corroding all the infrastructure devoted to it.
Turning off the shower while I am soaping is now second-nature to me, like turning off the water while brushing teeth. I highly recommend it.
I wish this was feasible, but in our house the water takes 5 minutes to get to the shower from the water heater, and if you turn it off for more than a minute, you'll get wild temperature fluctuations over the next 5 minutes while it re-achieves a stable mix. I think this is just one more reason to install an on-demand water heater rather than have a giant monolith in your garage.
I wonder if there is a way to better insulate the pipes so they don't lose their heat so much. That's pretty unusual. Five minutes is a long time for water to run down a pipe- you must be running 75ft or so of pipe- so insulation is the other answer (the first being the on-demand water heater in the shower- I used one once and had no problem with it, and it may be more efficient anyway).
Alternatively you could take lukewarm or cold showers. In the very least you save energy, and many claim it is invigorating, better for your skin, burns calories for those trying to lose weight, helps adapt you to cold weather, etc.
Not a fun experience the first few times though.
Not a fun experience the first few times though.
cold is agony. I have no interest in "adapting", and broaching the idea to my wife is a complete non-starter.
And lukewarm is exactly the same problem; 5 minutes to get that temperature, and some minutes to get it back if you leave the water off.
I am looking for a solution, not for someone to try convincing my entire family that we should prefer the problem. :-P
On-demand water heaters, or electric pre-pumps, or a needle valve with continuous return, are the three viable solutions, period.
And lukewarm is exactly the same problem; 5 minutes to get that temperature, and some minutes to get it back if you leave the water off.
I am looking for a solution, not for someone to try convincing my entire family that we should prefer the problem. :-P
On-demand water heaters, or electric pre-pumps, or a needle valve with continuous return, are the three viable solutions, period.
Going even further, I switched early last year to not using soap at all (except for extreme dirt which warm water couldn't remove) and my showers are done in 1-3 minutes (depending if I wash my hair or not). My girlfriend also says I smell better (and not like various soaps).
Also related, a chemical engineer from MIT started a company[0] back in 2013 purporting that showering kills our healthy bacteria. Supposedly he hasn't showered in 13 years, although their latest product recommends "rinsing in the shower for 3 minutes" followed by spraying their product on your body.
[0]http://aobiome.com
Also related, a chemical engineer from MIT started a company[0] back in 2013 purporting that showering kills our healthy bacteria. Supposedly he hasn't showered in 13 years, although their latest product recommends "rinsing in the shower for 3 minutes" followed by spraying their product on your body.
[0]http://aobiome.com
How much do you exercise? I've heard that athletes often don't need to wear deodorant, because they sweat so much during practice that there isn't a build of of odor causing bacteria.
Usually 2-4 times per week, but mostly just weekends. Definitely not athlete material (anymore at least). When I'm properly sweaty it generally isn't pleasant, especially when it dries.
I should have also noted that I haven't used deodorant in at least 10 years.
Maybe I just got lucky and won the genetic lottery in regards to smelly bacteria.
I should have also noted that I haven't used deodorant in at least 10 years.
Maybe I just got lucky and won the genetic lottery in regards to smelly bacteria.
> I've heard that athletes often don't need to wear deodorant, because they sweat so much during practice that there isn't a build of of odor causing bacteria.
As someone who spends ~3 hours a day doing vigorous exercise, there is no way this is true. I smell awful afterwards.
As someone who spends ~3 hours a day doing vigorous exercise, there is no way this is true. I smell awful afterwards.
But how do you smell after you shower it off? It could also be that people who exercise a lot might be less likely to sweat outside of exercise time.
> It could also be that people who exercise a lot might be less likely to sweat outside of exercise time.
Nope, I sweat pretty profusely throughout the day. Antiperspirant keeps me a part of civilization. FWIW I'm at a healthy weight and in good shape, just genetics.
Nope, I sweat pretty profusely throughout the day. Antiperspirant keeps me a part of civilization. FWIW I'm at a healthy weight and in good shape, just genetics.
This doesn't work with electric showers. The element retains heat and the water trapped in it gets extremely hot, so you get scalded when you turn it back on.
Ask me how I know, go on...
Ask me how I know, go on...
In the context of this discussion, retrofitting a heater with a better thermostat would probably be more practical than retrofitting a saltwater shower.
The trick is disposing of the saltwater. Consider that depending on the locale, wastewater might be put back into the water table or else treated for bacteria then let back into the environment.
Saltwater saturating our soils, water table or even being too concentrated in a bay would affect the ecosystem negatively.
Source: Someone who isn't an expert in waste management or ecology.
Saltwater saturating our soils, water table or even being too concentrated in a bay would affect the ecosystem negatively.
Source: Someone who isn't an expert in waste management or ecology.
Can you use fresh and saltwater in the same pipes? I feel like they would need to stay separate and having all the infrastructure duplicated and appliances able to switch between the two sounds expensive.
In HK there is a separate water system for sea water, and homes that use it for flushing toilets do have a second set of pipes. The additional cost of this complexity must be weighed against the value of having enough clean water for daily life.
We (as a society) really need to be pushing more efficient water appliances.
I looked up liters to gallons since I'm backwards and - in case anyone else is too - 10 liters is ~2.5 gallons. I replaced three toilest in my home that were flushing ~4 gallons with each flush with ones that flush with 1.28 gallons now. They are much more powerful than the previous ones I had, and use (liter-wise) less than half of the 10-liter mark.
Do your efficient toilets overseas not get down to the 4-6 liter range per flush?
The switch to more efficient toilets really made a big impact on my water bill for barely a dent to the wallet.
I looked up liters to gallons since I'm backwards and - in case anyone else is too - 10 liters is ~2.5 gallons. I replaced three toilest in my home that were flushing ~4 gallons with each flush with ones that flush with 1.28 gallons now. They are much more powerful than the previous ones I had, and use (liter-wise) less than half of the 10-liter mark.
Do your efficient toilets overseas not get down to the 4-6 liter range per flush?
The switch to more efficient toilets really made a big impact on my water bill for barely a dent to the wallet.
I remember living a month in Tokyo back in 2006 (or was it 2007). The house I shared had this toilet where the wash basin drained into the toilet tank. The faucet is activated when you flush the toilet. So once you're done with your #1 or #2, you wash your hands and the grey water is used to fill the tank. It was quite clever.
Newer toilets in the US are only allowed 6 liters max.
And those toilets can never seem to handle my #2s. You're not saving anything if you have to flush 2-3 times and use a plunger every time.
Regulating the volume of the tank is useless unless you also define a test standard for functionality.
It's like saying that cars have to meet a minimum mileage standard without also specifying that they have to be able to maintain 60 mph while going up a 10% grade. Except in that situation, cars that do not meet the implicit minimum consumer standard don't get purchased off the lot. In houses, the person who buys the toilet is more likely planning to repackage it into an entire house and resell it to someone else than use it personally. So your toilet might look like a full-sized sedan, but have a go-kart engine under the hood. They just bolted a smaller tank onto a base that was designed for a larger flush volume.
So what those toilets are allowed de jure is not necessarily lowering de facto water use.
Yes, there are toilets out there that were redesigned for low flush volumes, and they do save water, but they have not displaced the letter-of-the-law, flush-it-twice toilets in the construction of cut-every-possible-corner suburban subdivisions.
Regulating the volume of the tank is useless unless you also define a test standard for functionality.
It's like saying that cars have to meet a minimum mileage standard without also specifying that they have to be able to maintain 60 mph while going up a 10% grade. Except in that situation, cars that do not meet the implicit minimum consumer standard don't get purchased off the lot. In houses, the person who buys the toilet is more likely planning to repackage it into an entire house and resell it to someone else than use it personally. So your toilet might look like a full-sized sedan, but have a go-kart engine under the hood. They just bolted a smaller tank onto a base that was designed for a larger flush volume.
So what those toilets are allowed de jure is not necessarily lowering de facto water use.
Yes, there are toilets out there that were redesigned for low flush volumes, and they do save water, but they have not displaced the letter-of-the-law, flush-it-twice toilets in the construction of cut-every-possible-corner suburban subdivisions.
So true! I rarely shit in US&A, but when I do, I must average close to 3 flushes per shit.
I don't usually have to use a plunger (thankfully, since I don't live there and only shit there as a guest). But I've learned through hard experience: the Americans basically gave up on the toilet 100+ years ago.
Cold as fuck porcelain, rarely a slow-seat-lowering mechanism, no stain-resistant adherence-resistant polymers, no way you're getting any heated seats or odor-suppressing intake fans than vent air through filters, and, for whatever reason (asshole/vagina-squeamish culture?) there are virtually no spraywash/bidet type features...and to add insult to injury they can't even reliably flush a man-size shit down !!! :-O
I mean, they usually do, but any failure rate above 0.01% will make you quickly learn that you should just flush, then wipe, and if you feel like you need to wipe a bit extra this time, just flush again mid-wipe, and once more at the end.
logfromblammo I am so utterly with you: flush-test the toilets (and fuck it, if we ban toilets that use too much water, we should ban toilets that can't reliably flush a heavy load).
P.S. Yes, I live in Japan, the world's only toilet-superpower, and yes, I've ranted on this topic before on HN (https://news.ycombinator.com/item?id=4787587).
I don't usually have to use a plunger (thankfully, since I don't live there and only shit there as a guest). But I've learned through hard experience: the Americans basically gave up on the toilet 100+ years ago.
Cold as fuck porcelain, rarely a slow-seat-lowering mechanism, no stain-resistant adherence-resistant polymers, no way you're getting any heated seats or odor-suppressing intake fans than vent air through filters, and, for whatever reason (asshole/vagina-squeamish culture?) there are virtually no spraywash/bidet type features...and to add insult to injury they can't even reliably flush a man-size shit down !!! :-O
I mean, they usually do, but any failure rate above 0.01% will make you quickly learn that you should just flush, then wipe, and if you feel like you need to wipe a bit extra this time, just flush again mid-wipe, and once more at the end.
logfromblammo I am so utterly with you: flush-test the toilets (and fuck it, if we ban toilets that use too much water, we should ban toilets that can't reliably flush a heavy load).
P.S. Yes, I live in Japan, the world's only toilet-superpower, and yes, I've ranted on this topic before on HN (https://news.ycombinator.com/item?id=4787587).
Actually they do. This is a common thing. The majority of bathroom usage is for urination only, so if you do the math it works out.
Think of it like this. Lets say there were 10 toilet usages in a day, 8 urination and 2 defecation. If a flush takes 5 units of water, and works for either situation, that is 50 units of water a day.
Now you replace the toilet with one that uses 2 units of water but takes 3 flushes to clear defecation. 8 of your uses take 2 units, 2 of your uses take 6 units (3 flushes) total units of water 16 + 12 or 28 units. You save 22 units of water a day.
Think of it like this. Lets say there were 10 toilet usages in a day, 8 urination and 2 defecation. If a flush takes 5 units of water, and works for either situation, that is 50 units of water a day.
Now you replace the toilet with one that uses 2 units of water but takes 3 flushes to clear defecation. 8 of your uses take 2 units, 2 of your uses take 6 units (3 flushes) total units of water 16 + 12 or 28 units. You save 22 units of water a day.
Or you could just get a toilet with separate flush buttons for #1 vs. #2. Which avoids both waste of water and waste of time and other problems from inadequate flow.
There's a saying in our house (we're on rain tanks):
"If it's yellow, let it mellow, if it's brown, flush it down".
If everyone acted like that, then toilets could have a good, decent flush, powerful enough to purge any normal mud dragon.
"If it's yellow, let it mellow, if it's brown, flush it down".
If everyone acted like that, then toilets could have a good, decent flush, powerful enough to purge any normal mud dragon.
From a legislative perspective, that would be a great reason to mandate that all new construction include at least one urinal per bathroom (and that they be suitable for use by untrained females), and a horrible reason to mandate a lower tank size/flush volume on toilets that may be used for defecation.
But no matter what you do regarding toilet laws, the benefit simply vanishes in the noise when you also consider agricultural/industrial water use. It is pissing into a hurricane-force wind.
Domestic use in the US is 40.5 km^3/year, of which maybe 4.1 km^3/year is used in toilets (both for intentional flushes and leaks). Total freshwater use in the US is 483 km^3/year. A 50% reduction in water use for toilets would amount to a 0.5% reduction in total water use. For comparison purposes, 23.5 km^3/year of domestic water is used outdoors, for watering lawns and gardens or for filling swimming pools.
From a purely legislative perspective, it makes more sense to mandate leak-resistant flush valves than the size of the tank. It makes even more sense to strike down at a federal level all local zoning laws and HOA covenants that mandate a certain appearance for lawns, to explicitly allow alternate yard arrangments, such as xeriscaping and no-mow approaches, on residential properties. That would save more water in total than you could even by mandating that toilets could not use any water at all. And even that would pale in comparison to laws requiring just a 4% reduction in water use in steam-turbine power plants or in agricultural irrigation.
If you do the math, the burden of regulating toilet flush volume far outweighs the benefits from doing so. While you were counting flushes, one leak in one pivot irrigation rig just wasted more water than you will ever save in your entire lifetime of flushing toilets. This is my problem with individual environmentalism. An individual human already wastes so little that sacrificing just a bit more for the sake of the planet is easily flushed away by industry that has zero incentive--economic or regulatory--to conserve limited resources. You can drive a zero-emissions vehicle for an entire lifetime of commuting, and that benefit is more than erased by just one container ship burning bunker oil to ship consumer goods from Shanghai to Long Beach one time.
I pay by the cubic foot for municipal water, and I pay again for the municipal sewers and water treatment. For what I pay, I expect to be able to actually get my solid waste into the sewers without some jackass telling me how much water I can use to do it without also telling the toilet vendor that their product has to be able to do the job with that volume. Regulation for the public good is fine. Idiotic regulation, that does not accomplish the intended purpose, is not okay.
But no matter what you do regarding toilet laws, the benefit simply vanishes in the noise when you also consider agricultural/industrial water use. It is pissing into a hurricane-force wind.
Domestic use in the US is 40.5 km^3/year, of which maybe 4.1 km^3/year is used in toilets (both for intentional flushes and leaks). Total freshwater use in the US is 483 km^3/year. A 50% reduction in water use for toilets would amount to a 0.5% reduction in total water use. For comparison purposes, 23.5 km^3/year of domestic water is used outdoors, for watering lawns and gardens or for filling swimming pools.
From a purely legislative perspective, it makes more sense to mandate leak-resistant flush valves than the size of the tank. It makes even more sense to strike down at a federal level all local zoning laws and HOA covenants that mandate a certain appearance for lawns, to explicitly allow alternate yard arrangments, such as xeriscaping and no-mow approaches, on residential properties. That would save more water in total than you could even by mandating that toilets could not use any water at all. And even that would pale in comparison to laws requiring just a 4% reduction in water use in steam-turbine power plants or in agricultural irrigation.
If you do the math, the burden of regulating toilet flush volume far outweighs the benefits from doing so. While you were counting flushes, one leak in one pivot irrigation rig just wasted more water than you will ever save in your entire lifetime of flushing toilets. This is my problem with individual environmentalism. An individual human already wastes so little that sacrificing just a bit more for the sake of the planet is easily flushed away by industry that has zero incentive--economic or regulatory--to conserve limited resources. You can drive a zero-emissions vehicle for an entire lifetime of commuting, and that benefit is more than erased by just one container ship burning bunker oil to ship consumer goods from Shanghai to Long Beach one time.
I pay by the cubic foot for municipal water, and I pay again for the municipal sewers and water treatment. For what I pay, I expect to be able to actually get my solid waste into the sewers without some jackass telling me how much water I can use to do it without also telling the toilet vendor that their product has to be able to do the job with that volume. Regulation for the public good is fine. Idiotic regulation, that does not accomplish the intended purpose, is not okay.
What I hear when I read your reply is this:
And yes, it is true that agricultural use dwarfs urban use. But the same logic applies. Someone trying to grow almonds in the desert should pay more than someone trying to grow beans.
> I pay by the cubic foot for municipal water, and I pay
> again for the municipal sewers and water treatment. For
> what I pay, I expect to be able to actually get my
> solid waste into the sewers without some jackass
> telling me how much water I can use to do it ...
And yes, it is true that agricultural use dwarfs urban use. But the same logic applies. Someone trying to grow almonds in the desert should pay more than someone trying to grow beans.
Not exactly. What people pay for water should be uniform and proportional to the cost of providing it. I am not a fan of influencing behavior through taxation and subsidy. That is itself wasteful and inefficient.
You don't even need to have bracketed, progressively higher rates for water use. It would be enough to just stop subsidizing those who use the most.
Less than 1% of human-used freshwater in the US goes through toilets.
Personally, I don't bother to optimize code unless the profiler says it is heavily used. I am probably not going to mess with a routine that only accounts for 1% of execution until well after I have optimized the hell out of the two functions that collectively account for 80% of CPU time. (Analogy-wise, that's power plants and irrigation.)
Of course, given enough developers, someone will eventually have to optimize out at the edges. There's no reason to say we can't tackle toilets at the same time as pivot irrigators; it's just that any work done on them will be inherently less valuable. You're not going to need your best people on it. And any gains will be small.
It isn't entirely about improving performance at that point. Anything I do to shave microseconds from that 1%-used function is likely to introduce additional bugs into the code--such as failures in one of the two major use cases for it. (Poop remains in the bowl after I flush.) That's not so bad if I set up unit tests beforehand, because I then know when I have broken something.
But where are your unit tests for toilet flushing, Mr. Legislator? Nowhere. They don't bother with the profiler or with unit tests. So they end up with shitty code.
You don't even need to have bracketed, progressively higher rates for water use. It would be enough to just stop subsidizing those who use the most.
Less than 1% of human-used freshwater in the US goes through toilets.
Personally, I don't bother to optimize code unless the profiler says it is heavily used. I am probably not going to mess with a routine that only accounts for 1% of execution until well after I have optimized the hell out of the two functions that collectively account for 80% of CPU time. (Analogy-wise, that's power plants and irrigation.)
Of course, given enough developers, someone will eventually have to optimize out at the edges. There's no reason to say we can't tackle toilets at the same time as pivot irrigators; it's just that any work done on them will be inherently less valuable. You're not going to need your best people on it. And any gains will be small.
It isn't entirely about improving performance at that point. Anything I do to shave microseconds from that 1%-used function is likely to introduce additional bugs into the code--such as failures in one of the two major use cases for it. (Poop remains in the bowl after I flush.) That's not so bad if I set up unit tests beforehand, because I then know when I have broken something.
But where are your unit tests for toilet flushing, Mr. Legislator? Nowhere. They don't bother with the profiler or with unit tests. So they end up with shitty code.
The replacement toilets have never clogged, even with the entirety of a toilet paper roll being emptied into them (slight exaggeration).
The lack of water in the bowl concerned me, but the "flushing power" makes up for it. I've had them installed for about two years now and the kids' toilets hasn't had anything that couldn't be flushed.
But, as you mention, these aren't contractor-grade toilets. Indeed, those do suck. I've used plenty.
The lack of water in the bowl concerned me, but the "flushing power" makes up for it. I've had them installed for about two years now and the kids' toilets hasn't had anything that couldn't be flushed.
But, as you mention, these aren't contractor-grade toilets. Indeed, those do suck. I've used plenty.
There's definitely better and worse models. The ones the builder put in my house are pretty iffy. But the Eljer I put in my finished basement has never clogged.
[deleted]
Yes, and this is good. However, porcelain toilets kept in relatively good condition seem to last forever. The ones I was replacing were original to the home (30 years).
How much do you pay for water? Did you calculate the pay-back time of those new toilets?
No idea. I'm more about less waste though, so that and the home renovation was what sold me. Self-install so the cost was relatively low.
http://www.hcsa.us/files/What-does-my-toilet-really-cost-me....
http://www.hcsa.us/files/What-does-my-toilet-really-cost-me....
Just as a reference point, in SF, the first three "units" of water (748 gallons), costs $6.42/unit. Or $0.009 per gallon. After that, $0.011 per gallon.
That doesn't include things like delivery fees, sewer charges, etc.
That doesn't include things like delivery fees, sewer charges, etc.
Wouldn't salt water in toilets require two sets of pipes leading into each home? Seems like an expensive proposition unless you're building a new community from scratch.
It does, but it isn't.
Similarly multiple out-going pipes to split off various levels of grey waste (some direct to garden, others, to soakways, or to septic processing systems).
Capex for these kinds of systems is ultimately dwarfed by savings on opex - just like we find with mandatory double-glazing & other insulation regulations.
Similarly multiple out-going pipes to split off various levels of grey waste (some direct to garden, others, to soakways, or to septic processing systems).
Capex for these kinds of systems is ultimately dwarfed by savings on opex - just like we find with mandatory double-glazing & other insulation regulations.
Makes sense. But out of curiosity, where are you getting that info? Personal experience? Research in some field?
Mostly personal experience including some stories from permaculture types who've been approaching these problems for a while. I'm designing a habitat that will have an additional complication of both low-pressure gravity fed and electric-pump (city pressure) circuits.
Regulations lag behind optimum configuration, though parts of EU, especially in the north, legislated triple-glazing (f.e.) quite a few years ago (can't find a cost analysis of break-even points, unfortunately). I'm sure there's plenty of assumptions wrapped up in these regulations around estimated abode longevity, energy pricing over that period, etc. But as to multiple water sources into abodes, I haven't seen much formal work on it. I think the idea gets touted in London periodically - it'd be a nice solution to the dual problems of high water table and (surprisingly) occasional potable water shortages. But retrofitting this to an existing, massive, badly planned metropolis would be a nightmare.
Regulations lag behind optimum configuration, though parts of EU, especially in the north, legislated triple-glazing (f.e.) quite a few years ago (can't find a cost analysis of break-even points, unfortunately). I'm sure there's plenty of assumptions wrapped up in these regulations around estimated abode longevity, energy pricing over that period, etc. But as to multiple water sources into abodes, I haven't seen much formal work on it. I think the idea gets touted in London periodically - it'd be a nice solution to the dual problems of high water table and (surprisingly) occasional potable water shortages. But retrofitting this to an existing, massive, badly planned metropolis would be a nightmare.
Well at the commercial level we certainly could and it has been done though most of the uses I have seen are to golf courses and certain parks. certainly large commercial buildings could have a separate set of pipes to provide toilets with water.
now what should be more easily done is require building codes to insure large complexes have separate gray and black water pipes so that easier to treat water is routed better.
now what should be more easily done is require building codes to insure large complexes have separate gray and black water pipes so that easier to treat water is routed better.
> have separate gray and black water pipes so that easier to treat water is routed better.
Are there examples of this done on a larger scale? I know facilities processing their waste-water onsite sometimes have this, but has it been done on a town/city level?
Are there examples of this done on a larger scale? I know facilities processing their waste-water onsite sometimes have this, but has it been done on a town/city level?
Yes you need two pipes, but it might or might not be expensive.
If your target it a farmer in the middle of nowhere you have twice as many pipes, twice as many pumps and no real ways to leverage economies of scale. Thus farmers typically have their own private well: they can drill a new well every 10 years for less than the cost of putting a pipe from the nearest city to their house. (wells generally last more than 10 years, but you have to replace the pump once in a while)
If you are targeting a downtown then there are high rises all over which increases the population density. The cost of putting in two sets of pipes is not much more than one larger pipe, and the pipes are amortized over everyone in the building on both sides of the roads - figure and extra $.50/month to have the second set of pipes: cheap enough that nobody will care.
The above are two different extremes, the only question is where along the spectrum is your question asked?
If your target it a farmer in the middle of nowhere you have twice as many pipes, twice as many pumps and no real ways to leverage economies of scale. Thus farmers typically have their own private well: they can drill a new well every 10 years for less than the cost of putting a pipe from the nearest city to their house. (wells generally last more than 10 years, but you have to replace the pump once in a while)
If you are targeting a downtown then there are high rises all over which increases the population density. The cost of putting in two sets of pipes is not much more than one larger pipe, and the pipes are amortized over everyone in the building on both sides of the roads - figure and extra $.50/month to have the second set of pipes: cheap enough that nobody will care.
The above are two different extremes, the only question is where along the spectrum is your question asked?
Some houses here in Germany have that already ("Regenwassernutzungsanlage") as some people use rain water for toilets.
Delivery is probably a jarger cost, we mostly depend on gravity for water pressure.
If you have plentiful access to salt water, it might be worth it to use that for "black water" (sewage).
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.
Yeah, seems feasible. Almost too good to be true…
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…
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.
> We require 130 litres / person
> per day in Europe
What does this 130 litres include? Food? Meat? Clothes?
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:
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...
> 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...
You can only concentrate sunlight for a fraction of the time. The good news is water is easy to store for long periods, the bad news is utilization is very low. Sierra Suntower https://en.wikipedia.org/wiki/Sierra_SunTower is kind of a worst case senario but they got about 100 hours per year of operation.
1620 MWh of output over several years? They'd be better off using the fuel used to construct it directly.
Amazing that that particular project got so much praise before the numbers were in.
I've played around with solar concentrators in the early 00's and realized very quickly that it wasn't worth my time due to all kinds of practical constraints, I always wondered why the companies and organizations that build these things don't do a scale model first. That way at least you get some real world data to plug into your spreadsheet before spending big $.
Amazing that that particular project got so much praise before the numbers were in.
I've played around with solar concentrators in the early 00's and realized very quickly that it wasn't worth my time due to all kinds of practical constraints, I always wondered why the companies and organizations that build these things don't do a scale model first. That way at least you get some real world data to plug into your spreadsheet before spending big $.
Dear God, do you realize what we've done? We've invented evaporation! (Sorry, the title struck me as funny.)
Not really - evaporation is used to trap the residue in the water, and dispose of the water itself.
This is the reverse - dispose of the residue, keep the water.
This is the reverse - dispose of the residue, keep the water.
I appreciate your recognition of my plea for a refresher in middle-school science. Most people can't perceive my pain in the midst of the sarcasm.
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.
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.
Yeah. After the initial excitement my first thought was if using nanotechnology could make the amortized cost of a panel prohibitively expensive.
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.
Here is the link to sundrop farms for those not familiar with the concept: http://www.sundropfarms.com/facilities/
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!
[0] https://en.wikipedia.org/wiki/Solar_still
[0] https://en.wikipedia.org/wiki/Solar_still
IMHO, scout troops should teach the kids how to acquire fresh water before how to make fire, but for some odd reason the kids find fire to be more interesting.
Who wants to worry about wells and sump holes and and filters and bleach tabs when you can burn things?
Who wants to worry about wells and sump holes and and filters and bleach tabs when you can burn things?
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.
[1] https://en.m.wikipedia.org/wiki/Solar_still
[1] https://en.m.wikipedia.org/wiki/Solar_still
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?
Water is not the only problem. You'd also need soil as not much can grow in a sand.
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.
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.
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.
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)
Even assuming you have to store it like nuclear waste, the ratio of about 3.5% doesn't sound too bad to the untrained ear.
Britain is using a huge old salt mine in Cheshire to store toxic waste right now. We could put all the salt... umm.. into old salt mines.
Now that's a job for you to tell your kid's school class about on career day. A salt un-miner.
Now that's a job for you to tell your kid's school class about on career day. A salt un-miner.
Reminds me of XKCD 1119, "Undoing" https://xkcd.com/1119/
> 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.
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 of the water we desalinate gets dumped right back in the ocean, add the salt back. Even the water that doesn't get into the sewage system ends up back in the ocean again via the water cycle/rainfall. (meaning we need to worry about local salinity issues but not global)
Actually most sewage systems output water that is safe to drink so we can put that water right back into our drinking water system and forget the whole problem over an over again. (If you ban lawns there might even be water left over as food is turned into water and the food probably isn't grown with city water). People generally don't like the idea of drinking sewage though so this will never happen.
Actually most sewage systems output water that is safe to drink so we can put that water right back into our drinking water system and forget the whole problem over an over again. (If you ban lawns there might even be water left over as food is turned into water and the food probably isn't grown with city water). People generally don't like the idea of drinking sewage though so this will never happen.
Given our track record I'd rather we didn't try find out.
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.
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.
This idea assumes that the product consumer is the side which needs desalination. Unfortunately, in practice usually the opposite is true.
The core of the idea is to put it on ships. Using idle capacity is just a purely optional bonus. Ignore that part if you want.
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.
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Why can't you just pour it back into the ocean?
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.
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.
I'd imagine the problem is the concentration of salt where the dumping occurs. There would need to be a system in place to spread the salt out over a large geographical area at concentrations that is not harmful.
It's not a global problem but a local one. Locally increased salinity and temperature can be a problem. You can drop a whole bunch of hot brine in the middle of the ocean to little effect, but the same is not true of a mangrove swamp or a bay.
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.
In the Persian Gulf there is real concern regarding the volume of brine that the desalination produces.
https://www.sciencetarget.com/Journal/index.php/IJES/article...
https://www.sciencetarget.com/Journal/index.php/IJES/article...
It could explain Eyewitness: Mass Dead Fish https://www.youtube.com/watch?v=70_SbAbPG_M
I don't know any reverse osmosis makers that are anywhere near 1:1. Current RO systems are 9.5:1. Over 90% of the saltwater is rejected as brine.
These 1:1 are the best numbers for demineralizing sweet water - I assumed that salt water desalination had much different proportions, which also means, that the relative change in salt content is pretty small and consequently the impact of putting it back into the sea.
Are you saying salt water kills salt water fish?
of course. kind of like how oxygen can kill us.
Hey don't blame me, blame Science. Salt is a huge problem in desalinization. We can't just dump it right back into the ocean, especially if this is to be a long-term solution. https://www.scientificamerican.com/article/the-impacts-of-re...
Based on the article disposing of the double salty water "willy nilly" is the problem. We should be able to pipe a system that delivers it over a wide area. Nice info though!
What's wrong with dumping it back in the ocean? The desalinated water is also going back there eventually, so the equilibrium is unaffected
>What's wrong with dumping it back in the ocean
Locally high concentrations of salt are bad.
A little CO won't hurt you but it's not advisable to BBQ indoors.
Locally high concentrations of salt are bad.
A little CO won't hurt you but it's not advisable to BBQ indoors.
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...
Part of me wonders if the water could be used for fracking as a double down on energy generation, but the other part of me says that if that were possible that people far smarter and richer than I would have already been on top of this.
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.
Any particular reason you couldn't do a siphon-pumped multistage flash still with solar heating? That would be just glasswork.
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.