Considering drinking water is some tiny, tiny fraction of the world's water, it's probably not going to be a crazy idea to just dump the salt etc back in the oceans where it came from without causing any crazy imbalance, because we're talking about less than 1% of water.
About 2.5% of all the world's water is fresh water, and of that about 65% is in glaciers and icecaps. The roughly 0.8% of the world's water that remains, another 65% or so is permafrost and ice, only about 0.5% of the 65% of the 2.5% of the world's water is in river's for example.
So the notion of taking a small fraction of the ocean, desalinating it, and dumping the rest back in the ocean (as will eventually the water itself, later on in the process) probably isn't a big deal.
But then it's just inference, I'm not intimate with the subject. Biggest hurdle for me was always that desal was crazily energy intensive. I can't imagine it's become orders of magnitude more efficient, and as energy costs didn't plummet on such a scale (orders of magnitude), I thought it'd still be. But it turns out the costs are dropping fast.
I mean, I can easily see desal working for drinking water & cooking (few litres a day) for everyone on earth, but things like agriculture are a whole different beast. A kilo of wheat for example averages over 1.000 litres of water, while meat can go all the way up to 20.000 litres. I can't imagine desal for the billions of farm animals we slaughter every year (yes, billions :-/) , each weighing tens if not hundreds of kilos, for example, or even just agricultural production.
This is emphatically not true. The salinated impurities that are a byproduct of this process will kill everything in the zone that is is reintroduced to. Just because it is a small fraction of the ocean doesn't mean we can easily spread it across the entire ocean. Even then, we are doing an irreversible transformation of the ocean as a whole, and we need to be smart about the waste for the process to be sustainable.
I can think of several countries that did this incorrectly and killed large portions of their coastal ecology as a result.
> The salinated impurities that are a byproduct of this process
That's a very inaccurate way of saying that. You are implying that that desalination creates new byproducts. It does not. Any byproducts were already in the ocean.
You just run your outflow pipe far into the ocean, and mix it with ordinary seawater and it's sufficiently diluted.
That's misleading. It's not technically a byproduct, but taking literally tons of salt that was spread evenly throughout the ocean and dumping it out at high concentration at the end of a pipe has significant (and bad) ramifications for the ecosystem at the end of the pipe.
Nobody said to dump it out a pipe at one single point. Spread it out leaky pipe style over a large volume of ocean so that the average salt concentration does not significantly rise.
Many desalination plants mix it back into the ocean, you pump more water than you are desalinating and the 'waste water' is a mixed brine at an acceptable salinity level.
That said with global warming melting a bunch of fresh water glaciers into the ocean, one of the side effects is lowering the salinity level. This suggests to me that boosting it slightly by desal efforts will be negligible at worst, and remediation at best.
And of course the quantities we're talking about are pretty much mouse nuts with respect to the entire ocean. But an interesting question to play with is when does a 'keystone pipeline for water' make sense? Clearly Boston would have not minded shipping snow to California to get rid of it this winter. China is working to reroute major water ways, could we manage flood levels on the Mississippi that way? I don't know but it is fun to imagine.
> That said with global warming melting a bunch of fresh water glaciers into the ocean
That's a very good point! Potentially desalination could help fixing problems of rising see levels too. There are many deserts that could become huge lakes (in Sahara, Persia, China) and eventually it should be possible to move enough water from sea to compensate for some of polar ice melt.
Dump it on the roads in the North during the winter.
Or, more seriously, if it is salt that was extracted from the sea, there shouldn't be much harm in putting it back. The fresh water that was extracted will end up back in the sea also, so overall there should be no increase in salinity (except locally where the salt is dumped).
There are other products that come out of the process with the salt. There is a good example of the Persian Gulf because of the number of installations and the ability to easily measure the increase in salinity and contaminants.
A liter of seawater has 35 grams of salts in it (I looked it up: http://en.wikipedia.org/wiki/Seawater ). Compare that to the recommended daily intake of several grams of salt.
It's also the case that most of the desalination methods produce concentrated brine instead of dry, clean salt (so extracting the salt would require further energy), but not needing that much of it is the bigger reason.
I got that. For every liter of seawater that is desalinated, there would be ~35 grams of table salt. On a given day a person might use 4 grams of salt.
Given typical water usage, you quickly have salt for an awful lot of people (salt for hundreds of people per person consuming the water).
I guess other users would be welcome, even if they just take it for free that probably saves the desal plant on disposal costs.
No...Most ocean life is ridiculously dependent on perfect salinity levels. We wouldn't be doing any favors by increasing these levels, no matter how small our impact may be.
The change in salinity would obviously be negligible averaged over the ocean, and would be massively, massively dwarfed by other human factors. Your extreme use of the precautionary principle would prohibit essentially all new constructions, if applied widely.
Much more interesting is the question of the impact to the nearby ecology in the immediate neighborhood of the discharge pipe. I'm not familiar with this, but I'd wager it can easily be mitigated.
EDIT: Thank you to CHY872, who provides a link below to a review of the environmental impact of the waste water from desalinization:
> In most other cases environmental effects appear to be limited to within 10s of meters of outfalls.
About 2.5% of all the world's water is fresh water, and of that about 65% is in glaciers and icecaps. The roughly 0.8% of the world's water that remains, another 65% or so is permafrost and ice, only about 0.5% of the 65% of the 2.5% of the world's water is in river's for example.
See for example: http://water.usgs.gov/edu/pictures/watercyclekids/worlds-wat...
So the notion of taking a small fraction of the ocean, desalinating it, and dumping the rest back in the ocean (as will eventually the water itself, later on in the process) probably isn't a big deal.
But then it's just inference, I'm not intimate with the subject. Biggest hurdle for me was always that desal was crazily energy intensive. I can't imagine it's become orders of magnitude more efficient, and as energy costs didn't plummet on such a scale (orders of magnitude), I thought it'd still be. But it turns out the costs are dropping fast.
I mean, I can easily see desal working for drinking water & cooking (few litres a day) for everyone on earth, but things like agriculture are a whole different beast. A kilo of wheat for example averages over 1.000 litres of water, while meat can go all the way up to 20.000 litres. I can't imagine desal for the billions of farm animals we slaughter every year (yes, billions :-/) , each weighing tens if not hundreds of kilos, for example, or even just agricultural production.
I'd be happy to be enlightened!