**5. Hybrid technologies: the future of energy efficient desalination**

Desalination processes traditionally rely on mechanically driven membrane processes such as reverse osmosis (RO) or thermal distillation such as multi-effect distillation (MED) and multi-stage flash (MSF). In the use of membrane technologies, the principle is based on the use of technology with easy operation, limited use of chemicals, compactness, low energy consumption and the development of enhanced membrane materials [79]. Some emerging desalination technologies like forward osmosis (FO) and freeze desalination (FD), despite the serious challenges in the road to commercialization, have also recently garnered interest.

In a desalination plant, roughly 20–30% of the overall cost in water production is related to the energy [22, 29]. There is growing interest in combining the benefits of two or more systems, to meet specific water quality goals and/or reduce energy consumption. Using hybridization in desalination technologies is often in order to one or more objectives such as increasing water recovery rate, eliminating the need for a second pass or reducing brine salinity. Hybrid systems have been considered as economically superior alternatives to standalone systems due to their ability to reduce energy consumption and therefore cost of desalinated water through improved recovery rate and/or water quality [80].
