Potable water from the sea: can it save us from drought?

How to desalinate seawater

Let's first look at how to desalinate seawater starting with its definition: desalination is the technological process that leads to the elimination of salts present in water or other liquids, with the aim of transforming it into drinking water. In fact, dissolved mineral salts such as sodium chloride, sulfates, bicarbonates, magnesium and calcium are present in seawater, but also from other substances such as oxygen, nitrogen and carbon dioxide. The composition of brackish water varies slightly depending on geographical area and environmental conditions, although the percentage of dissolved salts present is fairly constant, averaging 35 g/L.

In any case, to potabilize seawater, it is essential to remove these dissolved salts. Seawater desalination is done through the use of reverse osmosis plants, which are special potabilization plants that operate filtration processes, using a semi-permeable membrane (or other type of filter) to remove salts and other undesirable substances from the salt water. Seawater desalination plants are thus systems composed of a series of filters through which water is pumped and filtered.

The limitations of water desalination in Italy

Water desalination brings with it some constraints related to the bureaucratic sphere and environmental sphere that do not facilitate the installation of plants in Italy. 

First of all, the “Save the Sea” law, also known as "Decree Law No. 117 of August 13, 2017," introduced a series of measures to combat pollution of the Italian sea and coastline. Although it does not provide specific limitations of desalination plants it imposes a series of conditions and a long and articulated authorization process for the construction of desalination plants, which has led to a slowdown in the installation of the systems.
In fact, according to the National Register of Desalination Plants (RNID) of the Ministry of Ecological Transition, as of December 31, 2020, only 11 desalination plants were active in the country, with a total capacity of about 176,000 cubic meters per day. 

Water desalination also poses other constraints that limit its use in some circumstances. For example, the desalination process requires considerable energy consumption, especially if reverse osmosis plants are used. This means that desalination can be expensive and unsustainable in areas with scarce energy resources or, as in the case of Italy, heavily dependent on imported fossil fuels. One possible solution is to build more renewable energy plants that provide clean, self-generated energy.

In addition, it is much discussed that desalination may have consequences for the environment, such as the production of large amounts of brine, the saline byproduct of the process. However, although this is still an unexplored field of research, some studies suggest that a possible solution could be to recover the brine to make commercial salt or to extract rare and expensive metals from the soil.

Can desalination plants be a solution against water crisis and drought?

Ultimately, desalination plants if properly managed can be a quick answer to water shortages. However, it is not possible to answer the drought problem so simply and immediately, as the solution inevitably poses a revolution of the entire economic and production system of modern society. This does not deny that desalination plants can be useful for the production of potable water to poor, arid areas with very little drinking water available.

Idro Group's desalination and purification plants are able to make seawater potable: depending on the concentrations and characteristics of the water, a different system is used, combining different purification technologies. In particular, three modular and compact plants have been developed that through the combination of purification, sedimentation, filtration, microfiltration, reverse osmosis, remineralization and disinfection processes are able to meet specific desalination needs.

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