At present, the combined production capacity of all seawater desalination plants worldwide is 36 million cubic meters per day. It is expected that this capacity will double in the next decade. 61% of the water is produced by thermal processes, mainly in the Gulf region, while 34% is produced by reverse osmosis (RO), which is the first choice in many countries that start to use desalination. Worldwide, RO desalination capacity for both sea and brackish water represents 60% of the total desalination capacity. Besides materials, higher salinity and temperature, all desalination plants use chemicals. Due to their large volume of brine discharges through many types of outfall systems into the sea,from simple surface discharge through an open-channel to modern submerged multiport outfall systems, desalination plants were included in the list of major sources of land-based marine pollution in the Gulf by the United Nations Environment Programme. Other main environmental concerns are the intakes, which may cause impingement and entrainment of marine organisms, and energy use, causing air pollution and greenhouse gas emissions.
The need for resource-saving, low-impact “green” desalination technologies is evident as the use of desalination accelerates in many parts of the world. The concept of “best available techniques” would be required at the identification of state of the art technologies, processes, or methods of operation, policies and programmes which indicate the practical suitability for preventing or reducing pollution of the atmosphere, sea and land as well as the quantities of waste and for reducing the impact on the environment as a whole. The design and siting of submarine intakes and outfalls are a complex task that relies on many disciplines including Oceanography, Civil and Environmental Engineering, Marine Biology, Construction, Economics, and Public Relations.