How sustainable can desalination be?

Population growth, climate change and urbanization are the main challenges to meet the water demand for the next decades. The global gap between sustainable water supply and water demand is expected to grow above 2,700 km(3) by 2030, equivalent to 40% of total water demand. Desalination is an established method to make fresh water-mostly as a last resort. Its contribution to water supply is minor on a global scale. In some regions, though, it is difficult to imagine a sufficient water supply without desalination. But is this technical fix sustainable? In its main part, this paper sheds light on the major issues that call the sustainability of desalination into question. Examination of a number of criteria indicates that the energy demand for desalination is by far the most important issue. Further relevant impacts are wastewater discharges, waste disposal and visual impact. In retrospect, it is noted that energy demand has already shaped today's desalination market, since energy-efficient membrane-based desalination technology has gained market share compared with the more energy-intensive thermal desalination technologies. This development has been supported by a substantial decrease in the specific energy demand of seawater reverse osmosis (SWRO) plants. As a result, state-of-the-art SWRO plants require approximately 3-5 kWh/m(3) compared to some 10 kWh/m(3) or more two or three decades ago. But almost all desalination plants are powered by fossil energy resources. Hence, using renewable energy (RE) resources instead would be a big step forward towards sustainability. Case studies prepared for three projects in the MENA region demonstrate that selecting RE sources for a desalination plant is economically feasible when compared to non-subsidized fossil fuel. This paper is based on our viewpoint as engineering consultants. It is a summary of studies, reports and surveys conducted on this issue by us in past years. It is intended to give an idea of the options that are available today to make seawater desalination sustainable.