As Leonardo Da Vinci said, “water is the driving force of all nature.” Natural ecosystems, climate regulation, the development of animals and plants, and also activities such as agriculture and industry depend on it. However, the increase in the frequency and intensity of droughts, a result of climate change, and the impact caused by human activities, are today reducing freshwater reserves. This forces us to find solutions that make progress compatible with the preservation of an essential element for life.
This requires the commitment of organizations like Ferrovial that contribute to the reuse of water. The company has a subsidiary specialized in water, Cadagua. In the current drought context, water reuse is a key factor. When we open a tap and see how water gushes out instantly, we are rarely aware that this is possible thanks to a complex process. Water coming from rivers, wells, reservoirs or directly from the sea must go through various operations, such as purification, desalination or purification, to ensure its health. It is then stored in large tanks, to finally be transported to homes through pipes. Ferrovial has specialized areas to ensure this process.
Purification is a necessary process, since wastewater contains organic matter and other contaminants such as traces of oils and fats, detergent, among others that, if they end up in rivers, generate imbalances that affect the ecosystem. This is what happens with eutrophication, when an excess of nutrients causes excessive growth of algae and in its subsequent degradation the oxygen in the water is consumed, which causes the death of other living beings due to asphyxiation. To avoid this, the wastewater is transported to the WWTPs, stations that purify wastewater. There, in the pretreatment, sand, grease, fibers, wipes and other materials are removed. Afterwards, we proceed to the primary treatment that eliminates settleable solids. After this stage, the water goes to secondary, biological treatment where, thanks to microorganisms, we eliminate soluble organic matter and nutrients, generating an effluent suitable for returning to the environment.
Many times, the water's journey through the WWTP does not end here. If it is to be used for industrial, urban or agricultural purposes (for example, for irrigation) it undergoes a tertiary treatment in which it is filtered and disinfected with different methods. For example, sand filters, activated carbon, ultrafiltration membranes, ozone or ultraviolet light. The sludge can be used to generate biogas, which contributes to achieving energy neutrality. The technologies necessary for purification depend on the quality of the source water. They usually undergo physical-chemical processes to reduce turbidity; They are decanted and the particles are removed with filters; and they can also undergo other treatments with activated carbon or ozone according to needs.
In the town of Sant Joan Despí, Ferrovial has incorporated advanced technologies in the station that treats water to make it suitable for consumption (ETAP), capable of supplying 3.3 million inhabitants, making it one of the most advanced in Europe by including processes such as Ultrafiltration and Reverse Osmosis. The different taste of water in each place does not depend on the process, despite popular belief, but on its own characteristics. Thus, in Galicia, the water is very soft, which causes it to have less flavor, in contrast to the harder waters of the coastal strip of Catalonia or the Valencian Community. Desalination plants use reverse osmosis membranes, a process that causes salts in a liquid to concentrate on one side of a semipermeable membrane. In IDAMs, stations that desalinate seawater, it goes through several treatments, including the final remineralization process to guarantee that it is balanced and with an optimal PH.
In some Canary Islands such as Fuerteventura and Lanzarote, they have been drinking practically all of the water they consume of desalinated marine origin for years. Increasingly demanding legislation will lead to the emergence of more advanced treatments. Nowadays, there are increasingly precise analytical methods and equipment that allow us to detect certain compounds in extremely low concentrations, which is the first step to eliminate them. The new strategies will involve recovering the maximum of by-products and highlighting the composition of the water, ensuring energy neutrality.
The South WWTP in Madrid is already capable of recovering phosphorus from water, treating 290,000 tons of sludge per year, generating 25 MW of electricity and using dried sludge as fertilizers. In addition, Ferrovial's new WWTP in Utebo, Zaragoza, provides a solution to the waste of 70,000 people and has digestion systems and solar panels. And the Águilas desalination plant, which has a capacity of up to 210,000 m3/day, complements the supply of the irrigation demands of the southern area of the Segura Basin, and the supply of the municipalities of Lorca and Águilas.
The new system will try to restore the maximum of byproducts, for example, recovering phosphorus for agriculture, a finite and scarce chemical, or separating methane from biogas for injection into the natural gas network, or generating green hydrogen, the fuel from the future. Among the plans for the near future is also to seek energy neutrality. The new directives will force each country to achieve energy self-sufficiency in wastewater treatment, so all wastewater treatment plants must work together to reduce energy dependence as much as possible and reach neutrality. This is achieved by maximizing biogas production, minimizing energy consumption with the installation of more efficient equipment and betting on the installation of solar panels and other technologies to take advantage of renewable energy. And without a doubt, digitalization and artificial intelligence will help further optimization.
