Carrión de los Céspedes (Spain): Nature-based Solutions for irrigation water reuse

Case Study is located in the Experimental Centre of New Water Technologies, in Carrión de los Céspedes, in Seville (Andalusia, Spain). It is as a living lab for the collaborative development, testing, and evaluation of innovative solutions in the fields of water management, wastewater treatment, and circular economy. It also hosts numerous training activities involving a wide range of stakeholders. Covering a current area of 4.1 hectares, the centre has several types of Nature-based Solutions (NbS) for wastewater treatment, including Constructed Wetlands (CW), sand filters, lagooning system, high-rate algal ponds, permeable reactive barriers, and floating gardens.

The area is characterized by a hot-summer Mediterranean climate (Csa) according to the Köppen classification. In Carrión de los Céspedes, summers are short, hot, dry, and mostly clear, while winters are mild to cold and partly cloudy. The site is located approximately 70 km from Doñana National Park, a protected natural area, home to a mosaic of ecosystems that harbour a unique biodiversity in Europe. 

The region faces several water-related challenges, particularly associated to seasonal dry, drought and water scarcity, stored water quality, water pollution and runoff, diffuse pollution of aquifers by fertilisers, evaporation, and the effects of climate change. Agriculture is one of the main economic sectors in the area. Most of the agri-food activity it is dedicated to rain-fed agriculture as sunflower and olive grove and irrigated agriculture as sunflower, olive grove and almonds. Fruit trees are acquiring an important extension limited by the need for irrigation.

The main objective of this case study was to enhance the treatment of wastewater for its reuse in irrigation, while improving both the quantity and quality of treated water stored for agricultural purposes. This work was carried out in the context of increasing water scarcity and climate change impacts in the region, which highlight the urgent need to identify alternative water sources for agriculture and to ensure the protection of aquatic ecosystems.

NATMed project, EU-funded project through the PRIMA Programme (n. 2221)

• Reduction of evaporation rates from stored water, improving water availability and efficiency.
• Assessment and identification of the most efficient CWs for nutrients, pathogens, suspended solids and organic matter removal, enabling compliance with water reuse quality standards.
• Constructed Wetlands successfully provide treated wastewater for subsequent reuse with the required quality for agricultural irrigation, which reduces the risks to health and the environment, and makes irrigation more sustainable, decreases dependence on conventional water sources and generates an economic boost through job creation.
• Effective removal of E. coli and reduction of microalgae, ensuring the safe reuse of treated wastewater for irrigation purposes.
• Improvement of agricultural soil quality, benefiting from the nutrient inputs provided by reclaimed water.
• Increase in species diversity within the study area, driven by the vegetation associated with the implemented NbS.
• Enhanced awareness and knowledge among local stakeholders regarding the benefits and safe use of reclaimed water for agricultural irrigation.

• Evaluation and optimisation of multiple Constructed Wetland (CW) configurations for wastewater treatment and reuse, ensuring compliance with EU Regulation 2020/741.
• Implementation of floating gardens to reduce evaporation and microalgae growth while enhancing biodiversity.
• Application of ultrasound technology to remove E. coli and reduce microalgae, enabling safe irrigation reuse.
• Establishment of a monitoring framework covering water quality, evaporation, soil quality, agricultural performance and biodiversity.
• Stakeholder engagement through co-design sessions with farmers, authorities, environmental organisations and researchers.

• Combining different types of technologies works better than using a single solution. Hybrid systems that bring together conventional technologies, such as ultrasound, with NbS like lagoons or Constructed Wetlands can significantly improve overall performance. 
• Although initial investment for NbS is significant, the medium- and long-term indirect benefits (reduced environmental impact, increased water resilience, waste recovery) are far greater, justifying the investment in alternative water technologies, especially in water-stressed regions.
• A clear operation and maintenance, together with well-defined monitoring protocols, is essential for the success of the system. Clearly assigning responsibilities, setting inspection frequencies, and planning preventive and corrective maintenance helps ensure reliable performance over time. Having a strong monitoring and evaluation framework proves crucial. 
• Active and continuous stakeholder engagement is key to correctly identifying and prioritizing challenges. The use of participatory approaches—such as workshops and co-design sessions—has proven highly effective in capturing local needs, building shared understanding, and guiding more relevant and accepted solutions.

AMAYA (Case Study Leader)

NBSCLIMATE (IUCN Assessment Leader)

CARTIF Technology Center (Project Coordinator)

Isabel Martín (AMAYA), Pilar Flores (AMAYA), Claudia Sánchez (NBSCLIMATE), Raquel Marijuan (CARTIF Technology Center)