What happens to brine after desalinisation? The Green lobby has so far been silent on plans by Cape Town municipality to removes salts and other substances from seawater. Desalination is one way to relieve the acute shortage of drinkable water that CT’s four million inhabitants can expect if it does not rain copiously before March next year – when the dams may finally run dry.
For example, there have been no calls for the use of wind generators to provide the electrical energy needed by a reverse osmosis process.
Perhaps it is dawning on the eco warriors that drinking water is essential for human life – so to hell with carbon dioxide emissions from the diesel or petrol electricity generators that may be used.
Even if the electricity comes from (horror) nuclear power – which it probably will in Cape Town, seeing as all the coal-powered stations have been closed down – we have heard nary a peep of protest.
But be that as it may, there are, or should be, serious Green concerns about desalinating sea water, so it is a mystery why the usual howls of protest are absent.
The first concern is this: the bio-product of desalinating sea water is large quantities of brine and water that is undrinkable. Disposing of this is a problem. It is commercially useless. Although Epsom Salts can be extracted, there is not a ready market for the quantities generated and the price would be higher than the market (if it were that large) could bear.
Placing it in landfill would risk it leaching it into currently potable groundwater, making it undrinkable. Not a good idea from an environmental point of view — or any view.
Pumping this useless brine back into the sea without further treatment is not wise either. The water component is bereft of oxygen for one thing, so it would settle on the sea bed and smother every living thing beneath it.
That would mean good-bye to crayfish and various other creatures that live inshore, and possibly even further out. It is reasonable to suppose other sea creatures would avoid such a salty desert as well. Goodbye surf fishing anywhere near such a dump site.
So it is not a simple matter just to desalinate seawater. It is energy-intensive, which is probably why such plants are frequently used in desert countries with large oil or gas reserves.
This raises another question for the Greens to contemplate – will this change their attitude to fracking? More problems arise for them here: should large amounts of gas be found in the Karoo, would they object to a pipeline from such a find to Cape Town’s desalination plants? Just asking.
Of course, there are engineering solutions of a sort that address the problem of disposing brine by-products of desalination of sea water. But all of them are expensive, and all of that expense would be loaded on the 800 000 ratepayers of Cape Town – the preferred place of residence of many of the Green persuasion.
So we can expect that the brine-water mix will be discharged into the sea where, if the weather is right, churning surf may spread out its impact. Hopefully, it will not harm sea life too much. In calm weather, on the other hand, it might not be a good idea to do it.
No one seems to have studied the long-term effects.
Of course, our city council may be well aware of the downsides, so one hopes they have long ago made ratepayer-paid trips to Spain, Saudi Arabia, Israel, Morocco and Australia. These are the places where experience lies. Israel (cue howls of protest) may be the best source of knowhow. The Israelis are planning to converting 500 million cubic meters of sea into fresh water annually.
There is another problem too: Seawater has other stuff in it that is not easy to get rid of – organic matter and bacteria that can clog up the membranes in the desalination plant, reducing their effectiveness considerably.
To prevent this, sea water must be treated with chemicals before it is desalinated. These, too, are then poured back into the sea.
Some have suggested the disposal of desalination by-products by injecting them deep in the earth. Others warn that this could affect the ground water 50, 100 or 500 years in the future. That degradation would make carbon emissions seem trivial.
But to get back to the energy consumption of sea water through desalination: turning saltwater into freshwater takes between three and four kilowatt hours to harvest 1 000 litres. That is three times the amount of CO2 emissions produced by the treatment of river or ground water.
Will that mean tripling what Cape Town ratepayers pay for water?