I was recently discussing the water crisis in Cape Town with my colleagues, and how they are currently heavily restricted in the amount of water they can use per day for fear that the entire city will run dry very soon. We often hear about how certain cities and countries are the driest they have ever been, and how this will only get worse as climate change progresses.
The thing is, I remember the water cycle from primary school. If certain parts of the world get drier, it means that other parts of the world get wetter. The planet as a whole cannot lose water. So, if it doesn’t rain anymore in South Africa, or California, it means that in other parts of the world it is going to start raining far more than usual.
The problem isn’t that the planet “runs out” of water, the problem is getting the water to the appropriate places. Given the way that the Earth is made, alot of that excess water is probably getting dumped into the oceans.
So, how to we transport that water to the places that need it most?
I proposed some kind of barge that could collect rainwater in the ocean and ferry it back to land. My colleague instead proposed a proper desalination method which is run on renewable energy, which can reextract water from the ocean.
I started poking about online and would you know, that second proposal actually exists, and they have been around for quite some time.
As far as I can tell, the first person to come up with a desalination method through solar energy was a Hungarian-American scientists called Mària Telkes back in 1920. Apparently, she came up with a small, portable solar desalinator which could be placed on lifeboats and eventually save the lives of stranded sailors when they found themselves surrounded by undrinkable water.
When I was in college, our Physiology professor told us that the way you survive being stranded at sea is by giving each other salt water enemas, because your colon will absorb the water but not the salt. Personally, I’ll take Mària Telkes’ option if I had the choice.
More recently, Italian inventor Gabriele Diamanti came up with a small device that can yield up to 5 liters of water of clean, drinkable water per day, also only using solar-powered evaporation.
Given that Cape Town is on the water, and given that they are having to live with an extremely limited amount of water per day, I’m sure that the people there wouldn’t mind a few of these devices to give them an extra 5 liters per day. But of course, none of these are large-scale solutions, and something of a desalination plant powered by renewable energy is what is needed if we want to go forward with this plan.
But wouldn’t you know, there are some companies that are on that too!
Less than one percent of the world’s desalination is powered by renewable energy sources today, but that could all change soon if companies like California-based WaterFX have anything to say about it. Its Aqua4 “concentrated solar still” (CSS) uses a concentrated solar thermal collector to compress heat, create steam and distill water at 30 times the efficiency of natural evaporation. It can produce 65,000 gallons of freshwater per day—and it can desalinate a wide range of water sources, not just seawater.
To wit, the company will start employing solar desalination to treat some 1.6 billion gallons of salt-laden irrigation drainage from California’s drought-stricken, agriculturally-rich Central Valley next year. Crops extract nearly pure water from soil, leaving behind salt and other potentially toxic minerals like selenium that naturally occur in the water. These excess minerals must be drained from the soil, or crop productivity plunges. By treating this drainage, WaterFX can prevent about percent of farmland in California from being retired every year to make room for storage for untreated drainage water. It will also prevent the drainage from contaminating fresh waterways and endangering wildlife. According to California’s State Water Resources Control Board, approximately 9,493 miles of rivers and streams and some 513,130 acres of lakes and reservoirs are listed as being impaired by irrigated agricultural water.
There’s obviously a typo in this Scientific American article, as they forgot to include exactly what percentage of farmland would be retired every year, but the principle still holds.
Of course, with the increase in global population, we have to be cognizant of how much strain we can actually put on the Earth’s water cycle. Solar powered desalination is not the be all end all, allowing the entire globe to be wasteful with water, because this closed system can still only support so much demand. Too much water desalination could, in principle and on a large enough scale, increase the percentage of salts in the seas and oceans, especially in places where there is little turnover of water from the open ocean (like the Adriatic Sea, for example). Having seas that are too salty is also a problem for marine life and stable ecosystems, the Dead Sea is called that for a reason.
Still, by keeping these things in mind, I think that solar desalination methods are still cool enough to rank as my favorite invention of the week.