Seawater desalination plants have gained prominence in recent days due to the restrictions to face the critical moment that Catalonia is suffering due to the drought. The truth is that this is not a new concept, they have been manufactured for decades, but given the uncertainty due to water scarcity, they are now presented as an alternative and an emergency solution to alleviate the water crisis. Companies questioned by this means that market them acknowledge that in recent months they have received “numerous” queries from Catalonia from different sectors, such as those linked to tourism, especially from hotels on the Costa Brava and from campsites in coastal areas for filling swimming pools, although also from some City Councils for personal consumption, and from other areas, from farmers for irrigation to yacht clubs or boat owners to clean their boats.
The producers of these plants are also waiting for the orders to be finalized and emphasize that they take care of their manufacturing, transportation and start-up, but they remember that the client is the one who must manage the cumbersome and slow permits with the administration for water collection. In the case of Catalonia, a modification of the special drought plan will allow the installation of privately owned seawater desalination plants and will be studied on a case-by-case basis, with the condition that this measure serves to guarantee economic activity and jobs.
The trigger for this change was the proposal by the hoteliers of Lloret de Mar to acquire a desalination plant, a matter that has already reached the Catalan Water Agency, which “is reviewing the feasibility, the reports and the necessary authorizations” from different sources. “technical units involved and legal services”. For its part, the Roses City Council has also publicly shown its interest in having an infrastructure of this type, as well as the hoteliers of Maresme. Some promoters even propose that excess water could be diverted into the riverbed to regenerate aquifers, resold to other individuals to fill swimming pools, or connected to the public network.
But how do these types of plants work? Compared to large public desalination plant infrastructures, such as Prat de Llobregat or Tordera, the so-called private, portable or prefabricated ones stand out for their rapid implementation and can be transported by truck in a container to the destination. Those that generate the most interest above all are those of a small and medium size, with a capacity from 10 cubic meters per day – as a guide it could supply around a hundred people – up to 500 cubic meters per day or 1,000 cubic meters per day. – with an estimated production for about 5,000 people and 10,000 people respectively -, although there are larger ones up to 5,000 cubic meters per day – for an approximate population of 50,000 people -.
Depending on the production capacity, prices vary and as a guide range from seven thousand euros for the most modest ones to half a million euros or one million euros for the medium-sized ones or higher prices for those with the greatest capacity. According to sources consulted, depending on their size and design, these modules can be manufactured in around six weeks for smaller plants and up to five, six or eight months for medium or larger plants. There are also companies that are dedicated to renting them.
According to data from the Spanish Association of Desalination and Reuse (AEDyR), in Spain around five million cubic meters of desalinated water are produced per day for supply, irrigation and industrial use through more than 700 plants throughout the territory. with productions exceeding 100 cubic meters per day. “Desalination seems to be in fashion, but the first desalination plant in Spain dates back to 1964, in the Canary Islands. It’s already 60 years! Since then, its technology has been extensively researched, innovated and optimized, especially in terms of sustainability and cost,” highlights Mª Carmen García Panadero, general director of Seta Pht, a company created in 1963, and vice president of the AEDyR.
Technically, these plants desalinate water through reverse osmosis. “It is a process in which a semi-impermeable membrane is used and a certain pressure is necessary to remove the salts and thus be able to make the seawater drinkable,” explains Raquel Hernando, head of water treatment engineering at the Corsa group. , whose manufacturing plant is located in the Castellví de Rosales industrial estate, in the Baix Llobregat region.
For its installation, “minimum civil works requirements” are necessary with a continuous slab or concrete blocks. Then you have to connect the water inlet, the permeate and concentrate outlet, as well as the electrical outlet. And they start to work. “It is the so-called plug and play system. Practically it is arriving, connecting the plant and testing that everything works well. It is already very assembled from the factory. Normally, the client has to take care of collecting seawater through a pipe or pump,” comments Jose García, Business Development Manager of ImWater Treatment Plants.
“The ideal thing in the sea is to make some deep wells and the sand serves as a small filtration. In these wells, pumps are placed to deliver the water to a tank through which there are other pumping groups that take the seawater to the osmosis tank. Between the seawater tank and the osmosis tank, another tank is necessary to put the permeated or produced water, which passes through the reverse osmosis membrane and the water is now drinkable. And from here another pressure and distribution group,” adds Hernando.
On the other hand, the development of new technologies has made it possible to make these facilities more energy efficient with the use of energy recoverers, more efficient reverse osmosis membranes or the use of renewable energies. In this sense, Panadero points out that the main expense of desalination is its high energy consumption, something that represents around 60% of the cubic meter of desalinated water. “A couple of decades ago we were consuming 20 kilowatt hours per cubic meter and currently we are below 3 kilowatt hours per cubic meter,” says the general director of Seta Pht. “Nowadays, desolate plants are being hybridized with solar panels. So solar panels can even be installed on the container or warehouse where the plant is located, which can cover an important part of the energy consumption,” adds García.
In this process, another no less important question is what is done with the brine, the water that is rejected with a higher salt concentration in the desalination process. Although there are technological centers that study its use for chemical or energetic uses, it usually ends up being dumped into the sea. “The normal thing is to make an outfall and it is poured back into the sea because we are contributing the same thing that we have taken before, we are not contributing any new compounds, they are the same compounds, except a little more concentrated. What is done is a diffusion system so that within a few meters the concentration has already been equalized,” explains the vice president of AEDyR. “If this system of returning it to the sea is done properly, it does not affect the marine flora or fauna,” she adds.
Regarding permits to install a desalination plant, capture and emission permits are necessary, that is, what is returned to the sea. And for those portable plants of less than 3,000 cubic meters per day, it is not necessary to make environmental impact declarations, according to royal decree 1/2008.
Beyond Catalonia, manufacturers of this type of installations have received inquiries especially from Andalusia, the Valencian coast, the Canary Islands or even the south of Portugal. Panadero makes a final reflection and defends that what needs to be “promoted” is long-term hydrological planning: “Desalination is not the only solution. First, consumption must be optimized. Secondly, save every last drop of water and then recycle everything you can. And, finally, complement the water deficit that we have left with desalination.”