The high cost of desalination has dominated discussions about the mass roll-out of this technology in South Africa. In 2018, the trade and industry department commissioned a study that found high capital and energy costs mean that desalination projects may not be appropriate given the fiscal climate.
In 2018, the City of Cape Town — then hurtling towards “day zero” amid a devastating three-year drought — ran out of money to pay suppliers for a huge desalination plant at the city’s harbour. Budget issues also led to delays in completing the city’s first desalination plant at Monwabisi, near Khayelitsha.
There are two leading desalination technologies: thermal evaporation, which involves the evaporation and condensation of saline water to purify it. And reverse osmosis, in which saline water is forced through a membrane that removes the salt.
Thermal desalination costs four times as much as reverse osmosis, but the latter is still costly compared with other water technologies. “These barriers render desalination as unsuitable to meaningfully impact favourably on South Africa’s water mix and development,” the study reads.
Last week, the Water Research Commission urged lawmakers to rethink its position on desalination.
Naidoo noted that the cost of alternatives to South Africa’s current infrastructure has become “the elephant in the room” when discussing its future water supply.
But achieving an economy of scale, through increased production and bigger plants, will rapidly lower desalination cost, he said. “So I am hopeful that in the 21st century, compared to we were before, that the desalination discussion would be quite a different one — using quite different parameters to the ones we were using before.”
Jay Bhagwan, the commission’s executive manager of water use, said desalination ought to be looked at as an opportunity to expand the industry. “That has been one of our weaknesses as a country. We were at a time leaders on the technology front … [But] at a national level, there was not a strategic view that this will be required in the future.”
Desalination technology has substantial economic opportunities because there is a growing demand for it, Bhagwan said.
Research manager Nonhlanhla Kalebaila emphasised that if the country wants to achieve water security, it needs a high assurance option like desalination, which supplies water even in a drought. “It is very important now that we put together the necessary requirements … to lay the groundwork for the upscaling of desalination.”
There are already eight large-scale desalination plants in the works.
Because energy costs can account for 60% of the operating expenses at desalination plants, the commission is researching how renewable energy could be used to power future plants.
Kalebaila said costs could also be lowered through the use of energy recovery devices, which have been widely employed in reverse osmosis desalination plants overseas. These devices recover some of the high costs of hydraulic energy used to pump water through the membrane.
A demonstration plant recently erected at Durban’s central wastewater treatment works is the continent’s first energy-saving desalination operation. The plant uses 30% less energy than conventional desalination.