The reverse osmosis process requires energy for the pump that drives the feed solution under the high operating pressure through the module. This pressure has to be considerably higher than the osmotic pressure of the feed solution. The energy consumption for sea water desalination is greater than for brackish water desalination, because the osmotic pressure depends on the salt concentration. However, the required energy is well below that needed for other separation processes such as distillation, because there is no phase change involved in the reverse osmosis process. The energy from the concentrate can be recovered by the installation of a turbine driven by the concentrate stream. This turbine could help to drive the motor of the high pressure feed pump. The pressure energy in the concentrate is used to compress a part of the incoming solution by depressurizing the concentrate on one side of a movable piston or diaphragm and by pressurizing the feed on the other side.

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