Salt and Water

What an interesting place is The Forum

In one of the latest posts there is some interesting discussion about water.

We have been seeing more and more water entering our seas from the melting of the polar ice caps. At the same time we have been noticing the lack of water that has been falling from the skies and filling up our dams and our reservoirs and hence we seem to have a problem. Being on an island we are surrounded by water that contains salt while we restrict our use of fresh water and complain that as our aquifers dry up we have an increase in salt.

Well let's just think about this. Saline water is purified in lots of countries going from saline to drinking water. So why not here?

Yes I hear you all saying but it takes a heap of electricity to enable the change and then what the hell do you do with the salt that is left?

One commentator on the forum has provided an interesting response to this quandry:

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?

What about that analysis? I am not well enough versed in either chemistry or power generation to offer a comment about the feasibility of what is being suggested - however I would like to hear from people who know a lot more than I do what they think.

In the so called 'sunburnt country' this sound almost too good to be true - is it?