An energy-efficient submarine desalination plant

The socio-economical development of many regions lacking a sufficient supply of fresh water (FW) may at times be planned with the help of desalination technologies for sea and brackish water (SW and BW). Since these technologies require large energy fluxes in the form of heat or electricity and produce sizable salt fluxes in the form of brines (B), relevant environmental problems have to be duly taken into account. One of the most energy-efficient industrial desalination technologies, reverse osmosis (RO) requires similar to 3-10 kWh of electric energy per cubic meter of FW produced from SW. At ENEL Research Division (Polo Idraulico e Strutturale, Milano), this desalination technology has been made the object of system design analyses which have brought out three novel, highly efficient schemes (submarine, underground, and ground-based) for FW production from SW. The present report concerns the submarine RO scheme RODSS (reverse osmosis deep sea system) which has been designed in collaboration among ENEL-Research (Milano), ETA (Firenze), JRC (Ispra), and WIP (Muenchen), under the auspices of the European Commission. RODSS has its RO desalinating units sited offshore at a suitable operative depth and achieves a remarkable energy efficiency through the fi-ee exploitation of the hydrostatic pressure of SW. RODSS will be described in sufficient detail to demonstrate that it requires much less electric energy than any conventional (ground-based) desalination plant of comparable FW production capacity. The discussion will clarify the main operative and maintenance features of the proposed submarine desalination technology which seems to have a promising technicoeconomical potential also vis-a-vis advantageous couplings with renewable energy sources.