As South Africans awaken to the serious impact of drought and the prospect of empty dams and reservoirs, looking beyond groundwater-saving solutions becomes a priority. A wave of water-from-air technologies are available. earthworks investigates the most viable options.
Atmospheric water generators
Producing water from air is a technology that has been used for a number of years in many countries, including the United Arab Emirates, India, the United States and China. Essentially, generators transform the atmosphere’s humidity into potable water, with no negative environmental impact.
Air is sucked in by a centrifugal fan through a filter and condensed into water. The water is pumped through an ultraviolet light tank, killing airborne bacteria. Passing through numerous charcoal filters, minerals are added to the pure water. The final product is accessible through a water-dispensing machine. Unlike water from the municipal system, this water is chlorine, fluoride and heavy metal-free.
The system takes 24 hours to produce 20 litres of water and relies on relative humidity to work. However, drier inland areas will still obtain a 60% relative yield from the water-creating machines. Placing a humidifier in front of the machine increases production by a further 35%. The units can function in any room and can be left on permanently. Filters require changing every eight months.
The units can be powered through solar or electricity from the grid, and a 20-litre unit, for example, would require a 400-Watt power source.
South Africa has been at the forefront of “fog harvesting”, with government setting up the world’s first fog screens in 1969 at Mariekskop in the mountains of Mpumulanga for SA Air Force personnel. They yielded 31 000litres of water each month.
Contemporary fog-collecting systems are static, consisting of poles and a shade net cloth strung between them with a gutter underneath. When fog blows in with the wind, tiny droplets of water form on the shade cloth. As more droplets coalesce, they trickle into the gutter, from where they’re channelled to catchment tanks.
Systems cost around R5000 for a 30m2 screen, which has a potential yield of up to 12-litres/m2/day.
In 2012 South Africa became home to another world first in fog harvesting technology with the invention of the Whirly. Made mostly from metal pipes, guttering and shade cloth, it has a solar panel and batteries. The device was created by Pretoria-based climatologist, Professor Jana Olivier, as a result of climate difficulties at their Lambert’s Bay experimental station, which saw little moisture collected due to low water content in the fog, coupled with very slow wind.
“We devised a rotating system – the only one in the world – which uses solar power that switches on a little engine and causes the net to rotate around a central axis,” says Olivier.
“The beauty is you don’t need grid electricity as this is a passive system,” says Olivier of the manual collector.
In the early 2000s, Olivier’s team erected a 72m2 fog collector near a school in the mountainous Tshawona in Limpopo Province. Over a two-month period, three 10 000-litre tanks of high quality water were filled. Eventually the entire community’s water needs were met.
“Within a couple of days the school principal phoned me and said: ‘The river is running! I can hear the water running!’”
Other fog harvesting projects have been established in various small communities in a range of climates, such as the Cape West coast’s Lepelsfontein and at Avontuur in the Southern Cape. To date, more than 500 people have been recipients of water harvested from fog.
Another method of extracting water from the atmosphere is “cloud seeding”. Research was done on the technology of cloud seeding in South Africa from the 1970s until 2001, but was halted because the Department of Water Affairs had “other priorities”, according to Nico Krouse of the South African Weather Service (SAWS).
Dhesigen Naidoo of the Water Research Commission (WRC) says that “as the 30th driest country in the world, South Africa can’t close off to any option”. He says the most successful country practicing cloud seeding is the United Arab Emirates, which claims to have increased rainfall by 30%.
Cloud seeding has the potential to augment existing rainfall and thereby increase reservoir storage and river flow. The approach involves “seeding” cumulus clouds at 300 feet by aircraft that fire flares containing sodium and potassium chloride (salt) just below the cloud base. “The basic methodology is about spraying substances into the atmosphere where ice nuclei form, causing heavier clouds and thus causing rain to fall,” says Naidoo.
Seeding one cloud requires 10 to 20 flares and the water-attracting hygroscopic material (salt) is effective in speeding up condensation, causing rain to fall. Water extracted from the cloud can be between 15 000 to 20 000 tonnes.
With regard to reasons why the South African government is not yet using cloud seeding, Krouse says it is still a “controversial’ technology”. “Some environmentalists compare it to geo-engineering with its negative reputation, while in the 80s and 90s there was opposition from farmers for religious reasons.”
Chief director of environmental sustainability at the Department of Environmental Affairs, Karen Shippey, consulted for Ninham Shand in 2004 on the South African Rainfall Enhancement Programme in an environmental assessment. “We found that the benefits of cloud seeding were greater than the potential negative impact,” she says. The concerns farmers had were over the stimulation of weather conditions and seeding rain in one area, which may have prevented it from falling in another.
“It did not enhance the heaviness of the rain, nor cause frost or stimulate hail or flooding. No evidence of cloud seeding in the pilot stimulated any of those negative effects,” says Shippey.
While water efficiencies are the most immediate way to save this scarce resource in South Africa, more options will need to be investigated should rainfall prove insufficient. The concept of extracting water from air is gaining ground and the timeous local technology trickle could become a welcome, fully-fledged flow.
By Shellee-Kim Gold
See earthworks magazine issue 38 June-July 2017 for the full feature.