The Growing Dependence on Desalination Plants
While extracting the salt from seawater to render it drinkable is currently being seen as a gamechanger in the global battle for water conservation, the concept is thousands of years old. In practice, the sailors of ancient Greece boiled seawater to obtain freshwater by evaporation, while their Roman peers employed clay filters to extract the salt. Even the first large-scale commercial desalination plant constructed in Venezuela more than 90 years ago is far older than most people are inclined to believe.
Today, around 80 per cent of the water consumed in Israel’s cities comes from the sea, a trend that is equally evident in many desert nations of the Middle East and Northern Africa. That said, the citizens of Cape Town owe a debt of gratitude to this technology, which helped prevent their taps from running dry during the “Day Zero” drought of 2018. It was drinking water from a temporary desalination plant that helped to avert the potential disaster which followed three consecutive years of inadequate rainfall.
Much of South Africa is semi-arid and subject to regular periods of drought, a problem that may be worsening due to global warming. To cope with the growing consumer demand and as a precaution against future drought scenarios, the country now has around ten such plants in operation, and several more are planned.
While ensuring an adequate supply of potable water is vital, it is equally crucial to ensure the technology involved is environmentally friendly. Any desalination plant that relies on distillation requires a constant heat source. However, emissions from the combustion of fossil fuels contribute to global warming, which, in turn, will increase the likelihood of drought. Furthermore, whatever the heat source, boiling vast quantities of water remains an expensive exercise and is markedly less cost-effective than conventional water purification technology. In fairness, engineers have made great strides in improving the efficiency of the evaporation process. Unfortunately, although their input has helped to reduce the price gap, it has not eliminated it.
Now, an alternative desalination plant technology that requires far less energy is successfully producing potable water at a cost that rivals that of conventional treatment plants. The technology in question is reverse osmosis, often abbreviated to RO. Reverse osmosis is also not a new concept and was first developed for commercial use during the ‘70s. The process involves passing a liquid under high pressure through a semi-permeable membrane with pores small enough to retain everything larger than a water molecule.