Desalination of groundwater/brine

Hi Everyone,

Does anyone know of a sustainable, green desalination process for groundwater?

The plot I'm hoping to buy has a borehole, but the bedrock is shale and as a result the groundwater is basically a brine. We could definitely drip irrigate from rain water tanks - but in a drought we may have to use the borehole water and I'm concerned about long-term effect of brine on soil quality. I've discovered a device called the desolenator, which is fantastic (basically a solar-powered still) and worth checking out. But I was wondering if there was a natural mechanism for desalination. I've read that spirulina is amazing at treating brines, but I cant find any detailed information on the efficacy. Can anyone please help me with advice or a contact perhaps?

Thanks

You are running smack bang into physics/chemistry. There isn't anything you can really add to water to get rid of salt ions; at least not on a cheap large scale. And if you apply the salty water to the soil as the water evaporates the salt concentration in the soil will steadily increase harming your land.

The two main methods are:

Reverse osmosis - requires pumps and power.
Evaporation and condensation - again, requires energy (but this can be passive solar)

Either will be expensive if you are planning to get large quantities for use as irrigation water, Although you might consider it as a backup for caring for specific vulnerable plants eg young trees that are getting established. Either of these also gives you a backup for potable water for the house.

An alternative direction would be to look at doing some earthworks on the land to trap and sink what rainwater you have, as well as looking at mulching to reduce the water needs of your plants.

What area are you talking about? What is the climate? How much rainfall do you get?

I don't understand why if the stone is shale why the water is salty ?
I know shale areas that are not salty

Whatever system you use, you still have to get rid of waste water that has more salt than what you started with.

hau Paula, do you have the results of a water test on the bore hole? It would be good to know what salts are present.

A shale bed, doesn't automatically mean saline water (brine or brackish) so where is the salt coming from, oceanic ground water? dissolved salts from other bed rock above the shale?

Redhawk

Thanks everyone so much for the feedback - I really appreciate it. The water has been tested a friend who lives on the plot next door to the one I'd like to buy - so we're able to confirm the high salinity levels - I'm afraid I cant sensibly account for the high salts originating from the shale. Where bedrock is granite or quartzite elsewhere in the district, people don't have the same problems with salinity. I'll do some more investigating.

Thanks for the suggestion of earthworks Michael - I'm very new to permaculture so only now getting my head around swale construction. The farm is in the Western Cape in South Africa near Knysna. We're fortunate in that the area normally gets substantial rain (700 mm per year), but in the last few the area has been hit by drought. So I thought I'd better plan for some contingencies. I'll do some research on the passive solar option, but as Kevin mentioned, dealing with the brine residue is going to be tough. We thought about draining the brine into an evaporation pond and then selling the salt - it has no nasty metals in it.

hau Paula, I don't know if you have contacted this agency yet but they might be able to give you some assistance and or suggestions.

South Africa Water Research Commission

Redhawk

Thanks Bryant - will follow up with them - appreciate it.

I could be wrong and often are but is it possible that your neighbour wrong about this ?
For what ever reason .....
I have known people try to suggest things to put prospective new owners off property they want to buy themselves.

David