What is the meaning of desalination?
Humankind has always faced the challenge of separating salt from seawater. Aristotle already talked about how useful seawater could be to irrigate fields and quench our thirst.
Water desalination is the process of separating the salts from a saline solution (brackish water or seawater) to turn it into water that is suitable for human consumption, industrial or agricultural uses.
The process of desalination takes place in desalination plants. It involves several phases:
- Withdrawal of brackish water.
- Pre-treatment: in this phase, the physico-chemical and biological properties of the water are made suitable for treatment in the desalination plant.
- Desalination: it is the main phase, where desalination techniques using membranes, distillation or evaporation are used.
- Post-treatment: desalinated water is treated to correct water hardness and low alkalinity, which are generated in the previous phases.
Desalination started at the end of the 19th century, although it has always existed as a natural process, through the process of evaporation of seawater in the water cycle.
Some of the existing desalination techniques include using membranes, as well desalination through distillation or evaporation (the latter are more energy intensive). Desalination making use of membranes includes techniques such as reverse osmosis (the technique most often used in Spain), nanofiltration and electrodialysis. On the other hand, desalination through distillation or evaporation (the techniques most often used in the Middle East) may use one of three processes: multi-stage flash distillation (MSF), multi-effect distillation with horizontal tubes and with vapour compression (mechanical and thermal).
Desalinated water can be used for agricultural and industrial purposes, and for human consumption. The requirements for desalinated water to be used for industrial or agricultural purposes are minimal compared with the requirements for drinking water. Hence, almost any of the methods outlined above can be used to obtain desalinated water for agricultural and industrial purposes.