DYNA JOURNAL ENGINEERING

Key words:

Water Management, Urban Resilience, Climate Change, Wastewater Treatment, Bilbao, Cantabrian Coasts, Water Supply, Water Engineering, Reverse Osmosis Desalination, Urban Water Systems

Article type:

COLABORACION/COLLABORATION DAMR

Section:

COLLABORATIONS

Cities on the Cantabrian coast, traditionally well-supplied by high rainfall, recently began to face tensions in their water supply due to climate change and pressure on resources, especially in large urban centers such as Bilbao and Santander. In cases like those mentioned, water supply has historically relied on transfers from the Ebro basin, the continuity of which could be compromised in the event of prolonged drought.
In this new context, there is a need to explore sustainable alternatives that strengthen the resilience of the urban water system. In recent decades, significant progress has been made in wastewater reuse and desalination technologies. Although in the 1990s the urban reuse of reclaimed water was not regulated, today there is a specific regulation (R.D. 1085/2024) that defines the quality parameters required for various urban uses such as irrigation, water flushing, and cleaning.
Real-life reuse cases in Spanish cities have been analyzed: Madrid uses more than 15 hm³ of reclaimed water per year, has a 700-km distribution network, and achieves a supply of 13 liters per inhabitant per day (lhd) for urban uses. Barcelona, for its part, allocates most of its reclaimed water to recharge the Llobregat River (indirect reuse), with a supply of 8 lhd. In the case of Seville, it uses 2.7 hm³/year and plans to reach 4 hm³/year, with a supply of 16 lhd.
These values are influenced by factors such as rainfall, urban area, and available investment. In areas with more than 120 days of rain per year, such as Bilbao, the sustainable reuse of reclaimed water solely for urban purposes is not economically optimal; simpler logistical solutions such as tanker transport are often chosen.
Current wastewater treatment plants (WWTPs) can achieve the required quality levels thanks to advanced tertiary treatments (activated carbon, ultrafiltration, UV radiation). In parallel, reverse osmosis desalination has evolved with standardized plants capable of producing more than 500,000 m³/d, making it a viable alternative for coastal cities with limited freshwater availability.
The study presents both technologies based on a contextualized analysis that considers climatic and urban factors for the Bilbao metropolitan area.