Water, Water, Everywhere But Here

They say that it will cost twenty billion rand to refurbish our national water treatment plants. They are lying in their teeth. It will cost a lot more than that.
South Africa is a dry country. As a result, we have built lots of dams to catch water to serve our cities, and canals and tunnels to shunt water from places where there is water to places where it isn’t. We have done pretty much what we could do in this regard. The best dams have been built and the best water transfer systems have been built. Now we must figure out what to do next.
South Africa is a mining country. As a result, we have dug a lot of holes in the ground which have filled up with water. Oxygenated water behaves differently from the de-oxygenated water which you normally find underground; thanks to the oxygen it loves to combine with other chemicals, most obviously metallic sulphides. Add oxygenated water to sulphur and before you know it you have the fixings for making sulphuric acid, which is not nice stuff to have in your water, as the Mozambicans have noticed when it falls from the sky because of our coal-fired power plants in Gauteng and Mpumalanga. The water which comes out of the mines is therefore acid. Acid water loves to combine with things, too. Meanwhile, the act of mining generates massive amounts of water, which is extremely dirty water mixed with powdered rock, and this quickly becomes chemically contaminated. And the act of processing the ore generates massive amounts of chemical wastes which invariably get into the water.
So South Africa is a dry country which has devoted immense energy, and spent vast amounts of money, on poisoning what water it has. This is called human nature and progress.
What we actually need to do about it is to start using less.
One of the simplest things to do is to start relying less on water from dams. All too often dams are built in relatively dry areas (like the Gariep) and therefore the water evaporates. This is worse, if anything, when the dams begin to silt up (as they always do); the shallower the water, the greater the evaporation.
Rather, why not rely on the water which falls on the city itself? The average town or city occupies a sizeable area of land. If the water falling on roofs were captured, it would provide everybody with drinking water at least, and probably with washing water as well. Water falling on roofs is reasonably drinkable, although in some areas, where the pollution levels are high, the first rains would probably have to be treated carefully because the water would be thick with deposited atmospheric poisons.
Water falling on the street is less easily drinkable. However, the water pouring into the drains need not be fed straight into the nearest river or the sea. Instead, it can be captured; the street drainage system could flow straight into tanks which could be drained into settling ponds and ultimately treatment plants. Street water is not likely to be as bad as sewage. It can be reclaimed for drinking.
Even sewage water can be reclaimed. The water can be settled and passed through sand or clay to remove impurities. (Of course, first pass it through metal mesh to remove rubbish.) Then, use micro-organisms. Bacteria, algae and protozoans could make short work of most chemicals; they break down almost anything into simple gases. The constant flow of nutrients into the tanks would keep them happy. Water flowing out would not be pure — but it needn’t be toxic or even dangerous. You could certainly bath in it. In case of emergency, you could chlorinate or ozonate it and it would be drinkable, though it might not taste pleasant.
This is the kind of thing which is done in places like Windhoek. If it can be done in Windhoek it could certainly be done in Upington or Oudtshoorn or Mthatha or Potchefstroom. In fact, it could be done in all major cities, and perhaps in small towns as well. Of course some people would dislike the idea of recycling wastewater and sewage. One might have to establish a “grey-water” reticulation for water which would be meant for washing or irrigation — or for industrial use, which is an enormous gobbler of water — and only drink it in time of crisis. It needn’t be that expensive. Furthermore, ideally every home, and even every block of flats, could have its drinking water provided largely from the rain, and just topped up occasionally. One might have three taps; hot washing, cold washing, and drinking.
Industry wastes a tremendous amount of water. Some of it is washing water which ends up clogged with toxic material. However, a lot of this can be recycled. It isn’t, because water is cheap whereas recycling equipment is expensive. On the other hand, if every small town had its water-recycling ponds, if there were a big industry making water-recycling plants, employing vast numbers of people — in that case, it would be fair to demand that industry should install the recycling plants too. Many big plants use as much water as a sizeable city.
Industry also uses water for coolant. Evaporative cooling (“cooling towers”) is tremendously wasteful of water, but one can replace it by huge radiators with fans blowing air over them — though, of course, this wastes electricity. (This is the system used in the new huge coal-fired power plants.) This expense is also unnecessary; all such cooling can be made use of, with the assistance of heat-pumps and low-pressure, low-temperature turbines, through closed-circuit electricity-generating systems. The only reason this isn’t done is a) because water seems cheap (although it is so no longer) and b) because such systems seem expensive (but they wouldn’t be if every industrial activity used it).
It is not really practical to build a lot more big dams. We do not have enough rivers and we do not have suitable places where rivers can be dammed. So all we can do is catch more water — which can be done by discouraging water from flowing into rivers in the first place, by building small earth dams to trap modest runoff, which either goes into the ground or into the atmosphere, where it contributes to rainfall elsewhere in the country. This is known as water harvesting, and while it is not a very sexy or profitable activity since all it requires is a few hundred people with shovels, it has a lot of potential to discourage runoff into rivers where such runoff means the loss of water to the local environment. However, such water harvesting does not bring any immediate returns; improved access to groundwater and improved amounts of water vapour in the atmosphere do not clearly provide any advantages for local humans. (In the long run they will improve the local vegetation in dry areas; on the other hand, in most parts of South Africa we are foolish to be pumping out any groundwater at all, because there is much too little of it, and in those areas where it exists, it is often dangerously polluted.)
One thing we can do, however, is prevent evaporation from the big dams we do possess. We can cover them up. A big dam covering fifty square kilometres needs a lot of covering, but the covering does not have to be heavy and it can float. A kilogramme could cover two square metres; let us then say 500 tonnes to a square kilometre. That big dam could then be covered by no more material than would be needed by a big cargo vessel. Of course there will be more — there have to be access walkways, jetties, etc., and also, if we are to dredge the dam from time to time to avoid silting, it would be necessary to disassemble the covering at least every few years. However, in principle it could be done without spending too much money. (Obviously, in the past, “any money” was considered too much.)
Another thing we can do, although only along the coast, is desalinate. This raises images of complicated plumbing in Israeli ion-exchange plants. However, perhaps this can be done both more cheaply, more effectively, and more simply, with ocean thermal power plants.
An ocean thermal plant was originally an idea for a floating power plant using the differential between deep water and shallow water. However, what is probably more sensible is to put the power plant ashore, and use the differential between water from only moderate depth (say, 50 metres), where it is fairly cool all year round, and water from shallow, hot ponds.
What you do is have two large cylinders, something like grain silos, but airtight. Put a huge airtight pipe between them. Pump the air out of the whole system. (You don’t need a total vacuum, but near-total is advisable). One of the cylinders is in the sun (shine mirrors on it if you like) and stays hot, the other cylinder is in the shade (both would be insulated at night) and stays cold.
What you then do is pump warm water from the ponds into very fine sprinklers in the warm cylinder. As tiny droplets of water plummet through the vacuum, the water evaporates. Not all evaporates, of course; droplets of slightly more salty water hit the bottom of the cylinder. The briny puddle at the bottom of the cylinder ultimately drains into a pond where it can either be re-used in the hot ponds, or pumped back into the sea.
So you have a cylinder full of warm water vapour. This naturally passes through the pipe into the cylinder full of vacuum. In the other cylinder, you have a mass of fine radiators inside which cold sea water trickles. The warm water vapour condenses there, so there is a constant rush of warm water vapour from the hot cylinder to the cold cylinder. At the bottom of the cold cylinder is a puddle of fresh water, which you can use for irrigation or drinking or what you will.
In the middle of the pipe between the two cylinders you put a big low-pressure turbine. The rush of the water vapour generates electricity. Enough to pump the water around the system and still leave a surplus which can be used by the local community. However, the big benefit of the system is undoubtedly the fresh water. The best thing about the system is that it requires no high technology at all; every bit of it can be manufactured by a simple blacksmith and put together by semi-skilled labour.
You could build thousands of these plants along the West Coast, from Saldanha all the way to the mouth of the Kunene. There’s no shortage of sun and plenty of need for water. Thousands of shallow concrete ponds might even pump enough water vapour into the air to make the use of irrigation water a little more effective by reducing the evaporation in the vicinity. Some plants could be built on the South Coast too, of course, in places where there’s too little water readily available. It’s hard to guess how much electricity would become available through this process, but even if it was less than a hundred kilowatts per plant, a thousand such plants would provide at least a useful megawattage. As a bonus you could end up with a dense brine which could easily be evaporated away into sea-salt.
We should be doing something like this, shouldn’t we? Anybody got any ideas why we aren’t, other than the fact that this kind of thing is cheap, easily done and therefore doesn’t make a guaranteed profit for any big businesses (except the despised and rejected construction and manufacturing industries) or any foreigners?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: