This project aims to structurally transform the management of treated effluent from the Fraga Wastewater Treatment Plant (WWTP), located in the Bajo Cinca region, by converting it into a safe, traceable, and reusable water source for advanced agricultural irrigation. The proposed intervention follows the Volumetric Water Benefit Accounting (VWBA) 2.0 methodology, specifically Appendix A-4, which allows for robust and scientifically verifiable quantification of water benefits derived from substituting conventional freshwater sources with regenerated water.
Fraga is characterized by a high-intensity agricultural model, primarily focused on extensive fruit and maize cultivation. This results in increasing pressure on the Cinca River and local aquifers, exacerbated by prolonged droughts, rising temperatures, and hydrological variability due to climate change. Within this context, the continuous discharge of treated effluent into the river without reuse constitutes a strategic loss of water and energy resources.
The project proposes capturing part of the secondary effluent, subjecting it to an advanced tertiary treatment based on membrane ultrafiltration and UV disinfection, and reintegrating it into the existing agricultural distribution network. The regenerated water will comply with Class A quality standards as established by current regulations (RD 1620/2007 and the upcoming RD 1085/2024), enabling its use in crops with direct human contact. The entire process will be monitored through a SCADA platform, real-time sensors, and binding agreements with local irrigation communities, ensuring additionality, permanence of benefits, and alignment with integrated water resource management principles.
Currently, treated water from the WWTP is discharged directly into the receiving environment without undergoing a valorization process, despite being suitable for reuse through an appropriate tertiary treatment. This represents a structural inefficiency in water management, especially in a region where agricultural demand is both high and seasonally intensive. Local farmers depend almost exclusively on direct withdrawals from the Cinca River or groundwater extraction through individual and collective wells, significantly increasing pressure on vulnerable natural sources.
The current model generates several negative externalities: progressive overexploitation of the Bajo Cinca aquifers, whose natural recharge cannot match the extraction rate, and the loss of an agronomically, energetically, and environmentally valuable resource. Additionally, this exclusive reliance on natural sources creates vulnerability to extreme hydrological events, such as prolonged droughts, reductions in environmental flow, or regulatory restrictions on agricultural use, jeopardizing the water security of the regional production system.
The proposed technical solution involves the implementation of a tertiary treatment system that meets the Class A quality standards defined by Spanish regulations for the use of reclaimed water in agriculture. The system consists of a treatment train starting with ultrafiltration membranes (cut-off < 0.1 µm) to effectively remove suspended solids, bacteria, viruses, and colloidal particles from the secondary effluent. This is followed by high-intensity ultraviolet disinfection, dimensioned to meet microbiological inactivation thresholds under RD 1620/2007 and the forthcoming RD 1085/2024.
As an operational and sanitary safeguard, an inline chlorination system will be installed to maintain a residual disinfectant concentration during water transport. The treated water will be directed to an intermediate storage system and pumped into a pressurized pipeline connected to the local irrigation infrastructure. The entire system will be monitored through an automated SCADA platform with real-time quality sensors and digital flow records, ensuring traceability, external verifiability, and continuous compliance with defined quality standards.
The project will be implemented in three integrated stages, structured to ensure additionality, traceability, and permanence of the water benefits. Each stage includes specific technical activities, measurement and control instruments, applied technologies, and defined timelines.
Stage 1 – Technical Assessment and Engineering Design (Months 0–6): A comprehensive audit of the secondary effluent is conducted, including physicochemical (pH, BOD₅, COD, TSS, conductivity) and microbiological (total coliforms, E. coli) characterization to establish the baseline. Based on this, the hydraulic, sanitary, and operational design of the tertiary treatment train is defined. Key equipment, ultrafiltration membranes (cut-off < 0.1 µm), UV disinfection system, and chlorination unit, is selected. This stage also includes environmental and water-use permitting with the CHE and the regional health authority.
Stage 2 – Construction, Assembly and System Integration (Months 6–12): Civil works for the tertiary treatment unit are executed, including concrete bases, technical rooms, interconnection piping, intermediate storage, and pumping chambers. The ultrafiltration and UV modules are installed and integrated into the existing WWTP infrastructure. Inline sensors (turbidity, free chlorine, UV transmittance) and the SCADA platform are configured. System calibration, leak testing, and operational validation are conducted. Treated water is verified by an accredited lab to meet Class A standards under RD 1620/2007.
Stage 3 – Commissioning, Operation and Monitoring (From Month 12 onward): With the system fully operational, regenerated water production begins and is injected into the local irrigation network, in coordination with the Canal de Aragón y Cataluña Irrigation Community. The system runs under real-time monitoring with inline sensors and SCADA-based traceability, continuously tracking water quality (turbidity < 2 NTU, free chlorine 0.5–1 mg/L, E. coli absence) and delivery volumes. External quarterly validation is performed by an independent laboratory. Digital records are maintained for auditability and ESG reporting. This stage ensures benefit permanence and verification in accordance with VWBA 2.0 requirements and platforms such as Aqua Positive and CDP Water.
Applied Technologies and Actions
Monitoring Plan
This project aims to structurally transform the management of treated effluent from the municipal wastewater treatment facility located in the town of Fraga, in the agricultural region of Bajo Cinca, Aragón, Spain. Its purpose is to convert this effluent into regenerated water of high sanitary quality for use in pressurized agricultural irrigation. The intervention is aligned with the international framework known as Volumetric Water Benefit Accounting, version 2.0, applying the methodology defined in Appendix A-4. This approach allows for the calculation of measurable and verifiable water benefits when conventional sources, such as rivers and groundwater, are replaced with safe and traceable alternative water sources.
The project addresses a critical challenge in a region characterized by intensive agriculture, especially fruit trees, maize, and forage crops, combined with high seasonal water demand and increasing pressure on the Cinca River and local aquifers. Climate change has intensified this scenario by causing more frequent droughts, higher temperatures, and growing variability in water availability. Despite this, the wastewater treatment facility in Fraga currently discharges all treated effluent into the river without any reuse system in place, even though the effluent has technical and sanitary characteristics that could be enhanced through tertiary treatment.
This represents a structural inefficiency, resulting in the daily loss of a water resource that could be reused for agricultural production. Meanwhile, the local farming sector continues to extract freshwater from stressed natural sources. The proposed intervention resolves this gap by implementing a complete tertiary treatment line designed to meet the Class A standard established under Spanish regulation (Royal Decree 1620/2007 and the upcoming Royal Decree 1085/2024). This level of treatment allows safe use of reclaimed water for irrigating food crops that are consumed raw or are in direct contact with water.
The system will consist of a membrane ultrafiltration unit with a pore size below 0.1 microns, capable of removing suspended solids, bacteria, viruses, and colloidal particles. This is followed by a high-intensity ultraviolet disinfection stage, and an automated chlorine dosing system as a secondary barrier to ensure residual disinfection throughout water transport. The entire system will be monitored through a digital control and automation platform, known as SCADA, with real-time quality sensors and a digital flow logging system to ensure compliance and traceability.
Project implementation is structured in three phases. In the first phase, diagnosis and design, a full technical and sanitary audit is performed on the secondary effluent, and the engineering specifications for the treatment system are defined. Regulatory permits are also processed with the Ebro River Basin Authority and the regional public health authorities.
In the second phase, construction and installation, the civil infrastructure is built, including technical rooms, interconnection piping, and storage and pumping systems. All treatment modules and monitoring devices are installed, and a series of calibration tests and pilot operations are conducted to validate the quality of the regenerated water against the Class A standard.
In the third phase, commissioning and operation, the system begins continuous production of regenerated water, which is distributed to local irrigation users through existing infrastructure. All water quality parameters, such as turbidity, residual chlorine (between 0.5 and 1 mg/L), and absence of Escherichia coli, are monitored in real time and externally verified on a quarterly basis by an accredited laboratory. Data is recorded for traceability and sustainability reporting, and agreements with local farmers ensure long-term use.
This project not only increases water use efficiency in agriculture, but also contributes to the protection of natural water sources, climate resilience, and food security in one of the 100 priority water-stressed river basins identified by the CEO Water Mandate. Its alignment with global sustainability goals makes it an exemplary case of circular water management and regional adaptation.
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