Saline/sea water can be treated to produce drinking water by removing dissolved salts. Desalination can be undertaken using different evaporation techniques or reverse osmosis. When compared by total energy consumption, reverse osmosis is clearly the most efficient method. Evaporation methods are typically used only when there is a large amount of “waste heat” energy available. In reverse osmosis, water is separated into permeate (filtrated water) and concentrate (residue water with high salinity). The share of permeate and concentrate varies. A RO system’s yield is typically between 30–50% with ocean water (salinity over 30,000 ppm) and 40–60% with brackish water (e.g. Baltic Sea, below 15,000 ppm).
Reverse osmosis desalination systems require a pre-treatment stage (typically multimedia filtration) which is defined based on raw water quality and antiscalant dosing. Drinking water applications also require water remineralisation and pH and alkalinity adjustment. The energy efficiency of a desalination system depends highly on whether or not the applied RO unit includes an energy recovery system.
Required information for system design
To complete a desalination system design, a raw water analysis is needed together with information about the required water flow/capacity of system and the required water quality after treatment or information about the use of the water produced. If the equipment is being installed in an existing space, information about available drainage and room dimensions is also good to know.