On this article Anthony Bennett looks at recent advances in desalination processes and the increasing use of energy recovery technologies. He also looks at the current market for desalination equipment, the types of desalination technology available and associated pumping requirements and the types of energy recovery devices currently available. The desalination of seawater (see Figure 1) to produce fresh water for human consumption can be achieved by using thermal or membrane processes, or a hybrid combination of these two process types. We shall firstly briefly consider thermal technologies. In the late 19th Century, the first major technical advance in desalination technology was the development of the multiple effect distillation (MED) process. Here, preheated feed water flowing over tubes in the first distillation 'effect' (or tank) is heated by prime steam, resulting in evaporation of a fraction of the water content of the feed. A process of evaporation-plus-condensation is repeated many times to produce the product water from effect to effect, hence the term 'multiple effect.' In the mid-1960s multistage flash (MSF) distillation became popular. Here, a flashing-cooling process is repeated from one stage to the next stage to produce the product water.
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