Water, Sewage & Effluent September-October 2017 | Page 24

With such an extensive coastline, desalination may be the answer to the water crisis in South Africa. Serious about ‘salt’ In principle, everyone supports the idea of desalinating seawater or sewage wastewater to a potable level, but the real challenge is to produce it at an economical, affordable level. By Jacques Laubscher, technical executive at GIBB Engineering & Architecture I n South Africa, it seems that whenever drought starts to bite, talk of desalination returns to the national debate. The Western Cape is only now emerging from another close scrape, where the winter rains arrived with the province’s dams around a dismal 10% of capacity. Drought conditions have become such a regular occurrence that we need to look seriously not only at water conservation, but at alternative sources of potable water. The principle of desalination is as an ancient process. Through the ages, sailors at sea boiled seawater and captured the condensate to provide drinkable, desalinated water. 22 Presently, there are primarily two types of desalination: thermal desalination, and reverse osmosis, where saline water is forced through a membrane at very high pressure to remove the saline content. Thermal desalination is by far the most expensive method, costing roughly four times more than reverse osmosis. But even the latter is still more than twice as costly as the current conventional treatment of surface and groundwater. We live in an arid country — mostly desert in fact. Our water resources are stretched to the limit, with our few water-rich areas being highly localised. This is an international problem. Only about 0.08% of the world’s water is Water Sewage & Effluent September/October 2017 accessible for direct human use, which means that 2.5 billion people worldwide live in water-stressed areas. South Africa’s freshwater resources are virtually fully utilised and are under heavy stress. It is predicted that by 2030, freshwater demand will be 0.08% World’s water is accessible for direct human use