Desalination is any process that removes excess salts and other minerals from water. In most desalination processes, feed water is treated and two streams of water are produced:

• Treated fresh water that has low concentrations of salts and minerals
• Concentrate or brine, which has salt and mineral concentrations higher than that of the feed water

The feed water for desalination processes can be seawater or brackish water. Brackish water contains more salt than does fresh water and less than salt water.

The most widely applied and commercially available technologies for sea water desalination can be divided in two types: membrane processes and thermal processes.

The advances in key equipment (membranes, pumps, energy cost  recovery device), turned the process energy efficient, resulting in a low investment cost  (CAPEX) and low operational cost (OPEX).

• The pretreatment: includes all the necessary treatment step ahead of the reverse osmosis plant. It is determining for plant life time and to minimize chemical cleaning and membrane replacement. It has a direct impact on the plant performance.
• The reverse osmosis process: can also be built with one or two passes, depending on the product water requirements and the seawater salinity and temperature. In most cases, 1 pass is sufficient to rich the EU drinking water standards, especially regarding the boron content (1 mg/L).  WHO boron guideline (2 mg/L).

Additional RO configurations involve passing RO concentrate through a second RO unit have been designed to achieve increased recovery and reduced concentrate volume, reducing plant size requirements. However, SEC is increased due to high pressure requirements of the second pass.

Energy savings can also be gained by grouping the RO plant components into three banks (high pressure feed; membrane; energy recovery), referred to as “three center RO.” This configuration has been adopted in large RO plants in Australia, Israel and Middle East and provides reduced energy demand for diurnal flows . However, three center design will not provide benefit where SWRO supplies only a small portion of total demand and therefore required to operate in batch mode (constant flow), as is the case for desalination plants utilized to supplement existing freshwater supplies.

SPSP is the preferred configuration where product quality requirements are higher, demanding second pass RO. Further investigation is required to verify the comparative benefits of three center RO