Is Australia Facing Overpopulation and Dwindling Resources?

[vanesch]

Is is a better life if biodiversity has been decreased?
Is it a better life if ecosystems are rendered unstable?
Is it a better life for future generations if we focus solely on the well being of our generation?

All this is a matter of pro and con evaluation of course. But I don't see how solar-driven desalination could ever be a problem, in de sense that what you pump out as fresh water this way is - I would think - a minuscule fraction compared to what evaporates naturally from the surface of the concerned waters, no ?

Because that is what a desalination plant actually does: extract some amount of fresh water from the sea. By "dumping" the salt back into the water, it keeps the amount of salt constant, while extracting fresh water. Exactly as does natural evaporation.

 

[SW VandeCarr]

Because that is what a desalination plant actually does: extract some amount of fresh water from the sea. By "dumping" the salt back into the water, it keeps the amount of salt constant, while extracting fresh water. Exactly as does natural evaporation.

This is certainly not the case in enclosed waters. If you extract fresh water and return the salt to the source you will increase the salinity of the source. The degree of increase is a function of the mixing with water of "normal salinity". In largely enclosed waters, returning the salt to the source is will increase salinity. Natural evaporation tends to be ecologically stable. This is what the paper I posted is all about. With open water, mixing is more efficient but with large scale desalination operations local effects could still be significant. Careful monitoring of offshore salinity should be a guide to returning extracted salt to the sea.

 

[vanesch]

Desalination is fairly intensive along the shores of the Persian Gulf which is normally hypersaline compared to the Arabian Sea. Hypersalinity is greatest in the northern Gulf off of Basra and decreases toward the Straits of Hormuz. The ecological dangers in this region are magnified by the enclosed nature of the Persian Gulf, its shallowness, and the present and planned number of desalination plants in all the Gulf States including Saudi Arabia and Iran.

http://www.eurojournals.com/ejsr_22_2_13.pdf

Ok, this paper describes a local effect, near the desalination plant. That has to do with local brine injection at a point. Such things could be arranged eventually by spreading the brine over a larger area, to help the diffusion.

But the paper also makes my point in the previous message. Natural evaporation amounts to about 2 meters/yr for a surface of about 240 000 km^2 for the Persian Gulf. That is what the "natural desalination plant" called the sun does to it. It amounts to the extraction of 480x10^9 m^3 of fresh water per year.

Now, I couldn't find a sensible number for the world consumption of fresh water, but it must be a number of similar magnitude.

 

[vanesch]

This is certainly not the case in enclosed waters. If you extract fresh water and return the salt to the source you will increase the salinity of the source. The degree of increase is a function of the mixing with water of "normal salinity".

Yes, but that's just a matter of dispersion. Of course, near a "point source" you will find local peaking of salinity.

In largely enclosed waters, returning the salt to the source is will increase salinity. Natural evaporation tends to be ecologically stable.

Not really! Salinity of the oceans is ever-increasing, because of solar evaporation, since the origin of oceans. Also, a priori, the extracted water by desalination should eventually return to the sea (as waste water for instance).

This is what the paper I posted is all about. With open water, mixing is more efficient but with large scale desalination operations local effects could still be significant. Careful monitoring of offshore salinity should be a guide to returning extracted salt to the sea.

Yes, for big installations, one should disperse it somewhat.

 

[mheslep]

returning the salt to the source is will increase salinity...

Is it necessary to return the salt to the ocean? Why not bury it or even pile it up somewhere? Then the ocean salinity could even decrease.

 

[SW VandeCarr]

Is it necessary to return the salt to the ocean? Why not bury it or even pile it up somewhere? Then the ocean salinity could even decrease.

The salinity won't decrease or increase because you're removing both water and salt. If neither returns to the ocean, then there is no change. It is true that extracted water will eventually return to the ocean via the hydrological cycle so in theory salt should be returned to the ocean over a longer period based on local monitoring.

However, in trade wind desert regions, much of the evaporation is not returned locally as rainfall, but exported to equatorial regions via trade wind zone convection cells. Examples are the Sahara and the deserts of Australia.

 

[mheslep]

The salinity won't decrease or increase because you're removing both water and salt.

The water of course is never permanently removed and will find its way back. The salts can be permanently removed, at least for an eon or two.

 

[vanesch]

In any case, I would say that forbidding desalination on the grounds that the sea might get too salty sounds to me as "overly precocious" and I weight my words - especially if it is done with solar power. A big coal plant to power a desalination plant, that's another matter. Even a nuclear reactor purely for purposes of desalination, I don't know if that's a good idea. But with solar power, I really don't see the problem.
I mean, compared to the good that that extracted fresh water can potentially do, compared to the "price" it costs, this is peanuts. One simply has maybe to think about how to disperse the brine better, or how to do something else with it.

 

[dilletante]

Perhaps returning the salt to the ocean may simply maintain the salinity since the ice shelves in the antarctic are expected to melt and add fresh water.

 

[Mk]

Even a nuclear reactor purely for purposes of desalination, I don't know if that's a good idea.

With the extra energy from nuclear powered desalination you could mine uranium from the sea too! The opportunity cost of this idea might be pretty high.

Is is a better life if biodiversity has been decreased?
Is it a better life if ecosystems are rendered unstable?
Is it a better life for future generations if we focus solely on the well being of our generation?

Just because there is a change in the environment, as long as that change is permanent, organisms will evolve into the change. New niches will be filled, and ecosystems tend to equilibrium. When you say, "Is it a better life for future generations if we focus solely on the well being of our generation?" that doesn't make much sense in this context. The entire thread is about how to make things better in the long-term, not just to worry about the short term and the end up with thousands of ghost towns.

 

[Blenton]

What is this? Are any of you australian?

I haven't heard anything about this at all, while you guys are sitting back stroking your beards. We already have desalination plants running.

 

[mheslep]

What is this? Are any of you australian?

I haven't heard anything about this at all, while you guys are sitting back stroking your beards. We already have desalination plants running.

Desalination plants run all over the world. The question is whether Australia can build enough of them to address the situation https://www.physicsforums.com/showpost.php?p=1555232&postcount=1", and if one believes that is a valid concern.

 

[Blenton]

Theres plenty of rain here now, the 'drought' is pretty much over.

The only problem we face is idiot politicians who think that building new dams would be a waste of money.