Has Cape Town tortured thirst enough to drink seawater?

Cities like Cape Town may have to rely on desalination to survive drought.

Cape Town dries up. If current forecasts come true, there will be no water left in this city of South Africa with a population of 4 million by May 11 - this date is known as " day zero ". The drought has lasted there for three long years - such a problem occurs once a thousand years, and the Cape Town water infrastructure was simply not designed for it .

The irony is that the whole sea splashes off the coast of this coastal city. But to drink this water, you have to build an expensive and energy-intensive desalination factory. Cape Town is in a hurry to launch such projects, at least temporary, which brings a terrible reality to light: individual parts of humanity around the world may have to rely on the sea to survive the drought of the near future. Everything from the fact that climate change, apparently, will only exacerbate this problem.

Modeling shows that in certain parts of the world the weather will become extremely dry and hot. For example, the south of America by 2050 may face a tripling of the number of days in which the temperature exceeds 35 ° C. “Cape Town is a warning shot for us,” says Michael Kiparsky , director of Wheeler’s Water Institute at the University of California at Berkeley. "According to our observations, water crises can quite likely go into the category of massive natural disasters that manifest themselves across the globe."

The key to water management is diversification. You can draw a parallel with the shares - if you have invested all the money in Enron, and the company has welled up , then your money will end. So with water sources. Dams, however detrimental to their environmental impact, allow you to save water stocks. You can even decide to process wastewater for restocking. And, of course, you need to convince residents to save water, even when there is a lot of it.

Cape Town cannot boast of a good story. “The diversification of water sources would help if it was started much earlier,” said environmentalist Kevin Winter of the University of Cape Town. “This is a difficult task, since it is necessary to create triggers that change the budget system and think outside the box about a long-term strategy.”

And in the trigger city has already worked. What the administration has been able to do over the past few months is quite remarkable, at least from the point of view of public education. Once the city consumed 1.1 million tons of water per day, and now this number has fallen to 600 thousand. But this is still a huge amount of water for the region, where the rain refuses to go.

Therefore, to combat shortages, Cape Town refers to desalination. Specifically - to the temporary stations of reverse osmosis , which should appear there in the coming months and ensure the flow of fresh water. Not so much in percentage terms - 15,000 tons per day - but not bad for a start.

Desalination is not a new idea. For many decades, researchers have persistently studied this technology, which is divided into two types. The first can be arranged at home - just boil water, collect steam and leave salt behind. The second is reverse osmosis, when water is forced to pass through the salt filter membrane. The problem is that the car of energy is used to boil water - just like the pumping.

Technology is improving. New-fashioned materials, such as membranes one atom thick , make reverse osmosis more efficient — that is, they make it easier to push water through the membrane. “The desalination technologies will change substantially in the coming years,” says Winter. “I think that now the city is not in a hurry with these experiments, hoping to accelerate with time.”

What some scientists express an active protest. At the end of last year, a group of researchers published a paper explaining how desalinated water can be polluted by sewage discharges into the water near Cape Town. In their water samples, they found 15 chemicals from pharmaceuticals and household chemicals, as well as unpleasant microbes such as E. coli. These things can not be allowed to desalination stations and turn into drinking water, without conducting preliminary checks and additional purification.

In addition to potential pollutants entering the desalination plant, there is also a by-product in the form of a saline solution, which is planned to be pumped back into the sea, potentially disrupting the work of ecosystems . And desalination stations can kill sea creatures by sucking them with water. “It does not make sense to solve one environmental problem by creating a bunch of others,” says co-author Leslie Green of the University of Cape Town, namely, increasing salinity and the inability to remove medical chemicals and organic pollutants.

Desalination may have an unexpected social effect in Cape Town, since not all residents of the city will find it useful. “I have water at home, it flows from a tap,” said Tom Sanya of the University of Cape Town, an architect who specializes in environmentally sustainable products. “But around the city there are a lot of people in informal settlements, and there is no water supply in their houses.” If the city could not provide every citizen of Cape Town with water, then I cannot be convinced that after serious investments in technology, we will have money to invest in the distribution of water. ”

Yet in Cape Town, environmental and social costs may fade in the face of the consequences that may arise if the city does not turn to the sea for help. Energy costs for technology remain high, but Israel has proven that this technology is capable of operating on a large scale: this state already produces more fresh water than is required. And while some parts of the world are plunging into a new era of heat and dryness, desalination will be a very tempting decision for them.

“It all depends on how much water you need,” says engineer Amy Childres of the University of Southern California. - And South Africa is experiencing such a need, and in its place would be California, if last year had not been so rainy. Everything is very simple - how much water you need and how badly you are unlucky with drought. ”

Cape Town is not very lucky. But he is taking steps to diversify his water portfolio, and in his footsteps it would be nice to go to the rest of the world. Otherwise, many of us will come full Enron.

Source: https://habr.com/ru/post/411173/

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