Submarine seawater reverse osmosis desalination system

Abstract

The project presented addresses the strategic topic of providing drinking and irrigation water through seawater desalination via a very energy-efficient and cost-competitive submarine technology. In conventional surface based industrial desalination plants applying the reverse osmosis (RO) technology, the freshwater flow behind the membranes is approximately 20–45% of the inlet seawater flow, depending on membrane type and characteristics. The resulting brine is disposed off into the sea. While state-of-the-art RO installations generate the required pressure with seawater resistant high-pressure pumps, the innovative submarine approach uses seawater hydrostatic pressure. The desalinated water, produced at about atmospheric pressure and collected in a submarine tank at the same working depth, is pumped to the sea surface. This approach saves about 50% of the electricity consumption with respect to an efficient conventional RO plant (about 2–2.5 kWh/m 3) since only the outlet desalinated water is pumped instead of the inlet seawater, thus reducing the pumping flow rate by 55–80%. It avoids the pretreatment of the inlet seawater, therefore saving costs for chemicals and equipment.