Desalination: millennial challenge, future solution

Seas and oceans occupy about 71% of the Earth's surface. Given this fact, it almost seems paradoxical that there are chronic difficulties in obtaining water. Something similar to a "forbidden fruit" before our eyes – abundant, but which we cannot enjoy. This is all the more true because, due to the exodus of populations to coastal areas, a phenomenon that has existed since the dawn of humanity to ensure greater chances of survival, around 40% of the world's population live less than 100 kilometres from the sea and 25% less than 25 kilometres.

It is said that "necessity sharpens the wit". In the case of the use of sea water for consumption, this could not be more true, and that is why, throughout time, just like in order to meet many other basic needs, Man has found ways to take advantage of all that potential. Aristotle was among the first to inform us publicly: sea water can be useful to irrigate fields and quench our thirst.

The philosopher's wise vision was right, as is easily proven. Today, more than 300 million people around the world, along with the most diverse agricultural and industrial activities, benefit from water supplies from more than 16,000 desalination plants in 150 countries, which produce more than 86 million cubic metres of water per day.

These are powerful figures that reveal the growing importance of this practice in the world, both from a social point of view and in terms of economic activities, whether there are agricultural, industrial or even services.

As in many other cases, desalination techniques have seen a long path of evolution, from mere empirical observation to scientific knowledge, which has resulted in advanced technology.

In order to desalinate water, various historical accounts indicate that Greek navigators used to heat it and make it evaporate, then let it condense into fresh water. This method was nothing more than replicating a natural process that has always existed, through the evaporation of sea water in the water cycle. The Romans, on the other hand, chose to use clay filters to separate the salt by filtering it.

In one way or another, the beginnings of some of the desalination techniques known today originated here.

The great technological step forward was, however, taken in the mid-20th century, with the appearance of what is known as reverse osmosis.  This is a water treatment technology – a more recent one when compared to the evaporation and distillation processes – which consists of removing dissolved salts by using semi-permeable membranes. When water passes through this membrane, salts and contaminants are retained.

Reverse osmosis is currently the most widely used technology in the world in this area and is also the one that Bondalti Water Solutions uses most in desalination plants.

The first large-scale desalination experiments in the post-industrial revolution were conducted on the island of Malta (1881), with the installation of the world's first unit dedicated to this process for commercial purposes. The purpose was mainly to supply the British barracks set up in the area.

Another important milestone was the installation in 1928 of a unit on the Caribbean island of Curaçao, equipped with a thermal compressor for evaporation, which still operates today to supply the island's inhabitants. This part of the world, where the former Dutch Antilles are located, is still the area where new desalination technologies have been tested for the longest time, with plenty of involvement from supplier companies.

In California, 1965 saw the inauguration of the world's first plant using reverse osmosis technology, which represented an important milestone for this industry.

Currently, almost half of all water produced through desalination (48%) is in the Middle East and North Africa, where there are fewer water resources. It is also worth noting the case of the island of Cyprus, where 95% of the water consumed is obtained through desalination.

Spain is what could be called a case study in this matter. In an evolution that began on the island of Lanzarote in 1964, there are now more than 700 desalination plants in Spain, producing more than 4.5 million cubic metres of water per day. It is currently the European country with the largest installed capacity in this area and one of the largest in the world.

Although it has the necessary technology, Portugal's experience with the desalination process for public water supply is still very limited, with its only operating desalination plant located on the island of Porto Santo, which opened in 1980 and has a maximum production capacity of 6500m3 of drinking water per day.

A new unit in the Algarve, a region historically affected by periods of drought and water shortage, is under development, and is expected to start operating in 2025, as part of an investment under the Recovery and Resilience Plan (PRR).

In the private sector, a project by Enkrott (a Bondalti Water Solutions company) is worth highlighting, which consisted in the installation of a desalination system in a hotel unit in the Algarve, to supply drinking water for irrigation and leisure infrastructures.