Harvesting Air

Thu, 28 Oct 2010 14:05

Harvesting Air

 

The Namib fog beetle is a feisty little creature. Every morning he makes an arduous journey to the top of a sand dune, where he turns his body into the wind, straightens out his rear legs and lowers his head. The fog rolling in from the sea gradually collects on his back, forming droplets of water, which glide downwards and hang from the insect's mouthparts. In this way, the beetle is always assured of a healthy morning drink, despite being miles from the nearest source of fresh water.

 

Fog harvesting is an innovative solution to the problem of water shortage - one that researchers have been quick to latch onto, but which many countries have been surprisingly slow to implement.

 

Professor Jana Olivier, a climatologist from the University of South Africa’s (Unisa) School of Agriculture and Environmental Sciences, explains that the idea of harnessing fog as a source of drinking water has been studied for decades.

 

"The first experiments were conducted in 1901, on Table Mountain. But it was only in 1987, in the arid coastal desert of northern Chile, that it was implemented on a large scale."

 

For years the remote fishing village of Chungungo relied solely on trucked-in water, but in 1987 it was transformed by the installation of a fog collecting system. With a dependable and affordable water supply, not only did the growing population have domestic water, they were also able to cultivate commercial crops and plant trees.

 

Although unconventional, the technology behind fog collection is amazingly simple: massive vertical shade nets are erected in high-lying areas close to water-short communities. As fog blows through these structures, tiny water droplets are deposited onto the net. As the droplets become larger, they run down the net into gutters attached at the bottom. From there, water is channeled into reservoirs, and then to individual homes. The system naturally works best when the wind is blowing, as the fog moves through the nets more rapidly.

In Chungungo, this system saw water flowing from local taps for the first time ever, in 1992, providing more than 40l of water per person, per day.

 

Like Chile, South Africa is an arid country in which large sections of the population have inadequate water supply. Only 35% of the country gets more than 500mm of annual rainfall, and, with few unpolluted surface water sources, and many contaminated ground water supplies and water tables that drop out of reach during drought, the advantages of an effective alternative water source are obvious.

 

Professor Olivier, who has been involved in fog collection research since 1995, says the potential for fog collection in South Africa is clearly shown by what has already been achieved in a number of fully operational sites, including Venda, Limpopo, another on the West Coast, and the latest in a remote village called Cabazane in the Eastern Cape’s rural Mount Ayliff area. And so far, Mount Ayliff’s persistent fog has yielded the best results, producing hundreds of litres of water a day.

Hope in the Hills

 

Mount Ayliff is located in the Umzimvubu local municipality, one of two municipalities within Alfred Nzo – the other is Umzimkhulu. Umzimvubu’s population is just 198 550, of which only 4% live in towns, while the rest live in rural areas.

Safe drinking water is a continual problem as the area lacks essential infrastructure, including water on tap. Villagers are often forced to dip into natural springs, running the risk of picking up water-borne disease. Mayor of Alfred Nzo, Gcinikhaya Mpumza, said, “We have a challenge … because about 40% of our community here does not have basic water.”

However, the villagers’ lives have changed with the installation of the water-harvesting system and its inexhaustible supply. No electricity is needed to power the scheme, which makes it eco-friendly and low-cost, and suitable for areas with no power infrastructure.

Because the technology is simple, the equipment does not need special maintenance. It consists of a double layer of 30% shade cloth nets stretched between steel cables supported by posts, with a gutter beneath each screen to catch the run-off. All components are readily available in the area.

The Cabazane set-up involves around 700m² of netting with each square metre of shade cloth yielding up to five litres of water a day – depending on the weather. On the good days, this adds up to 3500l, which is an incredible sum.

The system is installed up on the mountain slope, where nothing more than gravity is needed to get the drops flowing into the tanks. Reports say that about 30 homes in Cabazane Village have already benefited from the project.

The quality of water is described as “very high”, falling within the World Health Organisation’s standards for potable water. “The water is incredibly pure because it comes from the clouds,” said Olivier.

Innovative schemes like the simple and cost-effective fog harvester are well suited to South Africa, as it’s one of the driest countries in the world, with annual rainfall well below the global average.

 

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