The wastewater that reaches the Baix Llobregat wastewater treatment plant (EDAR), located in El Prat and one of the largest in southern Europe, is no longer discharged into the sea. Once treated, it undergoes an additional treatment that includes physical-chemical, microfiltration, and ultraviolet light disinfection methods, until it becomes pre-potable water that is returned to the river. This water resource, called regenerated water, constitutes the central pillar of the strategy designed by Aigües de Barcelona to combat the current context of extreme drought suffered by Catalonia and also to definitively end the structural water deficit of the metropolitan region.
Currently, the Llobregat water regeneration station (ERA) produces 1,500 liters per second, a flow that is pumped from El Prat upstream, to Molins de Rei, where it is discharged into the river. Eight kilometers downstream, this water is again captured for purification at the Sant Joan Despí treatment plant (ETAP), which injects it into the supply network that reaches homes. In the current context of severe drought, this volume of regenerated water is equivalent to 25% of the total water consumed in the metropolitan area (6,000 liters per second). Another 33% corresponds to water from the El Prat desalination plant, which also operates at full capacity, 23% is groundwater (wells and aquifers) and only 19% corresponds to river water, that is, from the reservoirs that make up the Ter-Llobregat system. Until now, in a year considered normal, desalinated water usually contributed only 5% of the water resource and 95% depended on sources linked to climatology, that is, surface and groundwater.
In total, in 2022 the El Prat ERA and another smaller one located in Gavà produced 50 hm³ of regenerated water, a figure equivalent to the consumption of one million inhabitants and which this year is expected to increase to 55 hm³, reaching 1,800 liters per second. According to Àngels Vidal, director of Aigües de Barcelona's ecofactories, producing regenerated water is three times cheaper than desalinating seawater and halves the carbon footprint.
Although the ERA Prat has a theoretical capacity to produce up to 80 hm³, this figure cannot be reached, as not enough volume of wastewater reaches the treatment plant. "We are already regenerating all the treated water we have available," explains Vidal, who recalls that the regenerated water from El Prat is also used for other purposes, such as maintaining the ecological flow of the river, maintaining the wetlands of the Llobregat Delta, curbing saline intrusion to prevent salinization of the aquifer, and for industrial and agricultural irrigation uses. In addition, as a consequence of the drought, between ten and twenty tanker trucks arrive daily at the ERA, distributing regenerated water to metropolitan municipalities, which use it for street cleaning or maintenance irrigation.
If the production of regenerated water in El Prat cannot increase, how will it be possible for this resource to become the definitive anti-drought shield? The solution consists of replicating the circular model that has been implemented in the Llobregat in the Besòs river basin, a project that will require a public investment by the Generalitat of 1,500 million euros and that Aigües de Barcelona urges to execute as soon as possible to take advantage of the Next Generation funds from the European Union. It involves building an ERA under the large esplanade of the Forum, where the Besòs treatment plant is also located, which, unlike the Llobregat one, currently discharges treated water into the sea.
"It is urgent to replicate the successful Llobregat model in the Besòs, because it will allow us to regenerate 100% of the water we consume," assures Josep Lluís Armenter, coordinator of Aigües de Barcelona's drought plan. According to the executive, this new ERA, together with desalinated water and other actions that are underway or projected in the Besòs and Llobregat, will allow an additional volume of water of 180 hm³ per year to be available. "This investment would allow us to stop depending on rainwater and guarantee the water resilience of 5 million inhabitants," emphasizes the executive. "With this project, this would be the last drought in terms of water reserves and consumption that Barcelona would suffer," states the company responsible for managing the water cycle in 23 metropolitan municipalities.
In this context, Armenter de Aigües de Barcelona points out that the Barcelona area consumes around 190 hm³ per year and that thanks to the Prat ERA (45 hm³) and the desalination plant (60 hm³) ---which provide a guaranteed resource of 105 hm³--- the structural water deficit is around 80 hm³. Consequently, this additional contribution of 180 hm³ that is projected would allow to definitively put an end to this deficit and stop depending totally on water from reservoirs, with the consequent increase in the ecological flow of the rivers of the internal basins.
This investment project has the endorsement of the Generalitat, the Agència Catalana de l'Aigua (ACA) and the AMB, but it needs to be launched urgently, as its execution is complex and will require between three and four years of works. Meanwhile, the company is carrying out other actions in the Besòs, such as the recovery of the Rec Comtal and the expansion of the drinking water treatment plant (ETAP Besòs). Likewise, improvement works are also being carried out at the Sant Joan Despí and Sant Feliu plants, and disused wells have been recovered, among other measures included in the drought combat plan.
Upcoming declaration of a state of emergency
The reservoirs of Catalonia's internal basins currently have reserves of only 19%, a historic low, so the Government will declare a state of pre-emergency next week, which will mean intensifying some of the measures and restrictions already in force in the current phase of exceptionality. According to the director of the ACA, Samuel Reyes, the situation "is really critical", so he asks for maximum awareness from citizens to save water not only at home, but also in offices, gyms or leisure activities. The ACA highlights that the accumulated lack of rain in Catalonia is equivalent to a deficit of 300 hm³ of contributions to the headwaters of the internal basins, so we are clearly "facing a historic drought" that will continue to worsen. In this regard, meteorological forecasts do not foresee significant rain episodes in the coming weeks, so the emergency could be decreed in December.
According to the Generalitat's drought plan, phase 1 of the emergency situation will be declared when reservoir reserves drop to 16%. This will mean that municipalities will not be able to exceed a consumption of 200 liters per inhabitant per day, compared to the current 230 liters. In phase 2 of the emergency, this volume will drop to 180 liters, and in phase 3 to 160 liters. It should be noted that these consumptions are the sum of all uses: domestic, industrial, urban, municipal, and agricultural. If only domestic consumption is considered, in Barcelona, for example, this indicator stands at 105 liters per inhabitant per day, below the average for Catalonia (117 liters, and for Spain as a whole, 131 liters).
Technical tests to reduce network pressure
One of the systems that can be applied to reduce consumption is to decrease the pressure of the water supply network. In this regard, Aigües de Barcelona began technical tests in September to implement this measure, which it has already prepared to apply when the ACA so requires. Currently, all AMB municipalities comply with the established consumption limits, but this situation may change when the emergency phase is decreed.
"We have carried out pressure reduction tests in 15 of the 180 sectors into which we have divided the network and have not registered any incidents in the water supply," explained Armenter, who estimated the water savings achieved with this measure at 7.6%, although savings could reach 20% if necessary to reach the 180 liters per inhabitant per day of emergency phase 2. According to the executive, if pressure is reduced, those who will notice it most will be residents living on the highest floors of buildings, although, in a first phase, this measure would only be applied at night. "We have been working on this project for two years and we have the network ready," he concludes.
Unlike other cities, which use pumps to raise water to the highest floors, in Barcelona the network is highly pressurized, as regulations require guaranteeing a pressure equivalent to a 15-meter water column, a figure that is usually exceeded. In this sense, the tests that Aigües de Barcelona has carried out so far have not decreased the pressure below those fifteen meters, so citizens have not noticed it, Armenter specifies.