This is my first time on this forum so hi to all of you.

My query is based on the fairly topical subject of salts based on a growing trend of desalination and water filtration.
It seems to me that not much thought is being given to the end result of the purification process in that more filtration leads to more salt - and from what I have read there does not appear to be a great deal of thought being given to what we should be doing with this byproduct.

Any thoughts in Academia?

G

Gonzo,
The concentrated brines that can be a by-product of desalination of seawater or saline groundwater have a value all their own. One such value resides in their usefulness as a component of solar ponds. Solar ponds are amongst the most cost-effective solar heat collection and storage devices. A layer of dense highly saline water is insulated by a layer of less dense fresh water separated by a membrane. Solar radiation is trapped within the saline layer, which heats up. This heat is used to generate electricity in a conventional closed-cycle thermal power plant using a low poiling point working fluid. (A facility like this supplies electricity for Birdsville in SW Queensland; the only difference being that the source of the heat is hot artesian water, water heated by the natural nuclear fission occurring in subterranean granite masses.) Relative scarcity of dependable fresh water supply for even domestic purposes is frequently a feature of life in Australia. I can only wonder that this convergence of availability of resource and demand for both product (fresh water) and by-product (in the ultimate, electricity) both in near coastal and remote inland locations is not recognised as an ideal opportunity for the application and development of natural (or, to use the buzz-word, sustainable) energy sources.
Not only is the brine by-product useful in its own right, it is easy to handle and transport. It can be piped to a usage point, it can be piped back out to sea, or it can be piped and re-injected into an already saline aquifer. Given, with respect to seawater particularly, the absolutely miniscule quantities of water removed as fresh water in relation to the source, the return of relatively more concentrated salt water to the sea need not be an environmental impact problem: it is so inherently controllable on both the small scale and the large that I can only marvel at the seemingly uninformed objections being thrown up against desalination on this ground. Is there some other agenda or community perception at work producing such negativity?

Forrest:

This is good stuff. Part of the issue here is in the effect of changing the water chemistry on the remainder of the plant. Your suggestion for heat 'banks' has a lot of merit in that:
a. we have to have evaporation ponds anyway
b. we need the facility to generate additional heat to help process the waste stream through our Brine Concentrators.

Would appreciate continued discussion on this but am going to read up on your ideas thus far.

As for public perception I think any issue where a 'waste product' is generated causes issues through ignorance rather than actually being an issue. I also think that this has a historical basis from when waste WAS dumped and the implications of this ignored. Fortunately I work for a Co that cannot do this so I am comfortable with looking at "radical' alternatives.

If you have any links etc to this idea I would appreciate the info.

Thanks again.
Gonzo

Gonzo,
The net is positively redolent with information on this general subject, from the conceptual (eg. www.halfbakery.com as a collection, but be prepared to refine or focus your search within it, noting the credentials of some of its contributors and respondents in the process), to the experimental 'commercial' or 'serious' applications (eg. www.abc.net.au/landline/stories/s357323.htm), to the level of small scale hobbyist interest. For this type of background research I think it helps if you have the sort of mind that is good at amassing technical trivia from not obviously relevant sources, and then accessing it on demand like some sort of low-grade idiot-savant.
Given that development, at least to experimental or pilot plant level, is by no means really recent, one has to conclude that the economics of desalination, or more precisely in terms of your original post, the economics of disposal of what is described as a by-product or 'waste' in this context, is seen as uncertain or unviable. For example, I did not learn of solar pondage from the net: I read about an application of it for remote area power supply (RAPS) near Alice Springs in, if I recall correctly, the Omega Science Digest back in the early 80s.
It is my fear that concerns are being fanned with respect to such things as brine disposal as an outworking of that art form at which Australia has increasingly begun to excel, the creation of artificial shortage in a land of potential plenty. Google 'hot rock', look at the potential of the resource, look at how advanced the prospects are, then ask why so little has been heard of it. Could it be that there are established interests, and I don't necessarily mean commercial ones, that wish to be very selective as to which developments are allowed to proceed, or at what pace? It is interesting to note that perhaps the biggest take-up of a natural energy based technology in Australia has been at the domestic level, for hot water supply. Perhaps that's the level from which to expect future results.

Gonzo,

A further innovative use of salt may derive from its property of being, typically, an hydrated crystalline solid. Heating will drive off the water of crystallization. The anhydrous sodium chloride resulting could be regarded as a dessicant. Once having cooled down, it will absorb water from its surroundings to re-crystallize. In places where there is just no liquid water, be it saline or fresh, but a suitable heat source is available, anhydrous sodium chloride could conceivably be used as an extractive medium to get water from atmospheric humidity or damp ground. The water could be driven off by heating the crystalline salt, and then condensed and stored as liquid water ready for use. The anhydrous sodium chloride (and/or other salts) could then be re-used to repeat the cycle.

Hydrated sodium chloride could also be viewed as an evaporation-proof storage for water in an extremely dry environment. Scattered rain showers falling under conditions where high and almost immediate evaporation is the norm could in this way come to be a usable resource.

It is not beyond the bounds of possibility that where there is a need to store heat, as in providing for the diurnal interruption of solar radiation in a solar/electric energy system, so as to permit round the clock generation of electricity, that sodium chloride could be the fuzed salt used. Condensed water of crystallization would be a by-product. Not exactly co-generation (another buzz-word), but certainly a complementary product.

It is difficult to see this particular use of salt becoming of wide applicability, but there are believably inhospitable locations within Australia at which such a system may prove viable. There is also often plenty of salt, with the prospect of more to come. You asked for innovation Gonzo. Here some is.

The real beauty of this proposal is that there is a real prospect that you could avoid perhaps not an Environmental Impact Statement, but the need for statement of any environmental impact within it. Nothing for the unproductive regulators to pontificate upon! What pure joy!

Well....

You can use salt to power a desalinator.

http://www.cryogenic.net/spdesalinator.html

Sylvia.