Reclaimed wastewater enters the fight against drought

Traditionally, the reuse of treated wastewater has been kept far away from residential areas. Nevertheless, the drought and the resulting difficulty in mobilizing conventional water resources has meant that reclaimed water is becoming an increasingly plausible option to minimize the impact of these episodes of scarcity. A study headed by Hug March, a member of the Faculty of Economics and Business at the Universitat Oberta de Catalunya (UOC) and a researcher in the Urban Transformation and Global Change Laboratory (TURBA Lab) research group affiliated to the university's Internet Interdisciplinary Institute (IN3), has analysed some initiatives already exploring this potential in the Barcelona Metropolitan Area. The study looked at their viability and also the possible impact of their widespread application.

In this research, March has partnered with David Saurí and Santiago Gorostiza, researchers in the Department of Geography at the UAB (Universitat Autònoma de Barcelona) also specializing in water resources. The study, published on an open-access basis in the journal Water Alternatives, makes it clear that the direct use of reclaimed water as drinking water is not on the table in Spain. However, its indirect use is regarded as acceptable, in the form of redirecting the flows back to the natural environment for them to be subsequently abstracted.

This is what has been implemented in the River Llobregat, where the El Prat treatment plant, close to the river's mouth, treats wastewater with cutting-edge technologies and, after freeing it from contaminants, pumps it upstream via pipes to be mixed with the river flow. This mixing takes place some eight kilometres upstream of the Sant Joan Despí drinking water treatment plant, which abstracts and treats water from the Llobregat for use in Barcelona's water supply.

The climate is speeding changes up

"The current drought situation has speeded up the indirect use of reclaimed water", said Hug March. This indirect use of reclaimed water for drinking water in the River Llobregat is a project of ambitious scale and scope that has been made possible by the Emergency Drought Situations Plan approved by the Government of Catalonia in 2020, which permits this use in exceptional or emergency circumstances. Previously, reclaimed water flows had only been used for agricultural, urban cleaning and watering or environmental purposes, e.g. as a hydraulic barrier against saline intrusion in the Llobregat aquifer.

"Introducing this kind of measure is always easier in a context of drought such as the current one, as it is obvious that, with climate change, we will have to get used to bolstering the metropolitan water supply system", said the UOC professor.

In this regard, David Saurí, a UAB researcher with more than 20 years' experience in the field, said that while there may be "a degree of social rejection of this kind of practice", the reclaimed water of the Llobregat "is perfectly suitable and strictly controlled and could, for a number of reasons, be of better quality than the river water itself." He stated that "drought or no drought, reclaimed water will end up forming a common part of the water supply", but also backed other options, too: "We will have to explore the Chinese concept of 'sponge cities' and make far better use of rainwater."

An official strategy

The Catalan government is working on the development of a Management Plan for the River Basin District of Catalonia and, at a metropolitan scale, the Barcelona Metropolitan Area has developed a Strategic Plan for the Integral Water Cycle of the Metropolitan Area of Barcelona, which already acknowledges the "great potential to increase the reuse of water, generating water resources that can help improve resilience to episodes of drought." There are plans for the building of more than 25 water reclamation plants in Catalonia, one of which is planned to reproduce the system already employed in the Llobregat in the River Besòs. "It is plausible to assume that, in the following decades, reclaimed water will constitute a significant component of water resource portfolios, especially in urban areas", said the authors.

Reusing a building's own water

The other case studied by the researchers was that in place for some years now in the town of Sant Cugat del Vallès, where local council regulations have, since 2002, stipulated that buildings of eight apartments or more need to have a dual piping system. This allows greywater (that from showers, baths and basins) to be stored and treated in the building itself for reuse in toilet cisterns. This project, despite being well accepted at a local level, has not been taken up elsewhere and does not appear to have a promising future in terms of its scalability at the metropolitan level.

Will the use of reclaimed water become more widespread in Spain?

In 2020, the European Union recognized, for the first time, the importance of these "new waters" by issuing a regulation on the use of reclaimed water for agricultural use, at the request of the countries of Southern Europe and despite the concerns of its northern members. So it is that the researchers are confident that this will be one of the use cases that we will soon be able to see in other parts of Spain, mainly in the areas of the Mediterranean basin and Andalusia, where droughts are most severe.

Hug March envisaged that this could be a solution of interest for urban areas with significant nearby agricultural land, such as Alicante: "We may see an exchange of water rights: for example, with farmers ceding the drinking water network they use for irrigation purposes and, instead, using reclaimed water for their crops and perhaps receiving some form of compensation."

What's the next step?

The seriousness of the drought is causing a rapid redrawing of the boundaries for the use of reclaimed water, but the economic costs of adapting these networks have become a challenge whose solution is not yet clear. "These systems of obtaining water from alternative sources – such as desalination – have the advantage of freeing us from dependence upon the climate but, on the other hand, they do increase dependence on energy consumption", explained David Saurí.

Given the paradigm shift that these alternative waters might represent, the researchers are currently working on more studies to examine how they are perceived by the public, how they will change urban water's political economy, what governance models may regulate them, who could control or claim the rights over them, and even how they will be funded and what the impact on the tariffs charged to the public may be.

This research projects fosters achievement of Sustainable Development Goals (SDGs) 6, Clean Water and Sanitation, and 11, Sustainable Cities and Communities.

 

Reference paper:

March, H.; Gorostiza, S. and Saurí, D. 2023. Redrawing the hydrosocial cycle through treated wastewater reuse in the metropolitan area of Barcelona

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