Biogas stands out as one of the most comprehensive and strategic solutions in the shift toward a truly circular economy. By leveraging high-moisture, nutrient-rich organic waste, this technology simultaneously closes three critical loops: water, nutrients, and energy. Through controlled anaerobic digestion, environmental liabilities are transformed into valuable resources—renewable biomethane, liquid biofertilizers, and traceable regenerated water. In a global context of water scarcity, climate pressure, and stress on food systems, biogas plants evolve from treatment facilities into regenerative platforms with measurable impact.
Within this framework, the Biometano Plant in Seville stands as a flagship case of applied circular innovation. It is not merely an energy production unit—it is an integrated model of water, nutrient, and environmental regeneration. Located in the heart of the Guadalquivir Basin—one of Europe’s most water-stressed regions—the plant processes up to 80,000 tons of organic waste annually, with a moisture content exceeding 75%. In conventional systems, this embedded water would be lost through evaporation or become untreated leachate. Here, it is captured, stabilized, and transformed into high-quality liquid digestate certified for agronomic use.
Every cubic meter of recovered water is traceable, from waste input to final use in local agricultural fields. This allows not only for the quantification of real, additional Volumetric Water Benefits (VWBs) under the VWBA 2.0 methodology (A-6), but also for demonstrable improvements in water quality aligned with the WQBA framework. Simultaneously, biogas is generated as a clean energy source, emissions are reduced, and dependence on water-intensive synthetic fertilizers is eliminated.
This project addresses today’s most pressing challenges while offering a scalable, replicable model of regenerative infrastructure. It is a triple-impact hub—economic, environmental, and social—that positions HEYGAZ as a leader in circular solutions for sustainable water and waste management. Biogas, circular water, and restored fertility, all flowing through one continuous, verifiable, auditable, and exportable system.
The management of wet organic waste is no longer just an operational challenge—it’s a strategic opportunity to unlock value across water, energy, and agricultural systems. In regions like Andalusia, the surge in organic waste generation—driven by urbanization, agro-industry, and population growth—has outpaced the capacity of conventional treatment systems. Most of these residues contain over 70% water, yet in traditional models such as open composting, this moisture evaporates into the atmosphere, taking with it valuable nutrients and contributing to greenhouse gas emissions.
In landfills, the situation is even more critical: the embedded water transforms into high-pollutant leachate, rich in nitrogen compounds, organics, and heavy metals, which threatens groundwater and surface water quality. These scenarios not only pose environmental risks but also represent a significant loss of circular potential. The liquid fraction of organic waste, when properly stabilized, has agronomic value as a biofertilizer that can replace synthetic inputs, reduce water footprints, and regenerate soil health.
But here’s the opportunity: rethinking organic waste as a water resource. Rather than losing it to evaporation or contamination, controlled anaerobic digestion offers a solution that captures and reuses this embedded water while producing clean energy and closing nutrient cycles. In doing so, it converts local environmental liabilities into circular, traceable, and impactful resources.
The Seville biogas project seizes this opportunity. It recovers more than 60,000 m³ of water annually from waste that would otherwise be discarded or pollute ecosystems. It valorizes this water in a way that supports agriculture, improves water quality, and strengthens climate resilience. In regions facing structural droughts, declining aquifer levels, and tightening regulations, this is not just a smart solution—it’s the future of regenerative infrastructure.
The Seville plant is designed as a closed-loop system for the treatment of wet organic waste via anaerobic digestion, addressing both the energy recovery and water reuse aspects of waste in an integrated and efficient way. The system operates under controlled conditions in a Continuous Stirred Tank Reactor (CSTR), optimizing organic matter decomposition without evaporative losses, thus preserving the liquid fraction present in the waste, which exceeds 75% of the total processed volume.
During the process, this embedded water is transformed into liquid digestate, a stabilized solution rich in key nutrients such as nitrogen, phosphorus, and potassium. This by-product is then applied in the agricultural sector as a biofertilizer, replacing conventional chemical inputs whose production and application entail high blue water consumption and significant environmental impacts. Valorizing the digestate delivers direct benefits in terms of water conservation while closing nutrient cycles and promoting more sustainable agricultural practices.
Furthermore, by preventing waste from being landfilled or subjected to uncontrolled composting, the generation of leachate with high contaminant loads—posing threats to groundwater and surface water quality—is avoided. The Heygaz system minimizes these liquid and gaseous emissions and supports compliance with environmental regulations on circular economy, water protection, and climate change mitigation. This comprehensive approach transforms the plant into not only a biogas production unit but also a strategic water regeneration hub at territorial scale.
Stage 1 – Reception and Characterization of Waste: In the initial phase, the Seville plant receives up to 80,000 tons of wet organic waste annually, mainly from agro-industrial, livestock, and food sources. The waste is weighed and classified by origin and type using an industrial scale and a digital traceability system. Moisture content, generally above 75%, is determined through specific sensors and laboratory gravimetric analysis. This stage is critical to define the project’s baseline, enabling a clear comparison with previous management scenarios such as conventional composting (where most water evaporates) or landfilling (which generates leachate without reuse). Daily volume monitoring and monthly moisture checks are conducted, enabling quarterly reports on water recovery efficiency.
Stage 2 – Anaerobic Digestion: After characterization, the waste is introduced into a CSTR where it undergoes anaerobic digestion under controlled mesophilic or thermophilic conditions. This closed system prevents water evaporation and preserves the liquid fraction of the waste. The process is monitored in real-time using sensors that measure variables such as temperature, pH, organic load, and biogas production. Automation is carried out via a SCADA system ensuring stable and efficient operation. The monitoring plan includes periodic reviews, monthly preventive maintenance, and semiannual third-party audits to validate operational conditions and water content preservation.
Stage 3 – Liquid Digestate Management: Following digestion, the effluent undergoes mechanical-physical separation to produce two fractions: a solid fraction destined for composting or organic amendment, and a liquid fraction representing the bulk of the water recovered from the process. This nutrient-rich liquid is conditioned and temporarily stored for agricultural use. Its quality is verified through lab analysis for parameters such as total nitrogen, phosphorus, potassium, and heavy metals, in compliance with current agronomic standards. Each batch is tracked via digital records and field application protocols. The monitoring plan includes quarterly sampling, volume tracking, and environmental compliance verification.
Stage 4 – Monitoring and Traceability: The final phase focuses on ensuring complete traceability of the water recovered and valorized as liquid digestate. Geographic Information Systems (GIS) and flow sensors are used to register and verify delivered volumes and their application in agricultural fields. Collaboration with farmers and regulatory authorities ensures the digestate is used safely and appropriately, maintaining the environmental and water benefits of the project over time. Cross-check mechanisms are established between production, application, and declarations, including annual third-party audits, semiannual document checks, and field verification visits.
Total Process Timeline: The process is continuous and runs uninterrupted throughout the year. Each stage includes specific monitoring mechanisms, with consolidated annual evaluation and traceability reports, supported by monthly tracking of critical indicators to ensure the project’s water objectives are met.
In a world where water systems face unprecedented levels of stress and degradation, the ability to transform liabilities into assets is a key competitive and environmental advantage. Biogas production, specifically through controlled anaerobic digestion of organic waste, has emerged as a multisectoral solution that addresses water, energy, nutrient, and waste challenges simultaneously. Far beyond its traditional role as a renewable energy source, modern biogas infrastructure is evolving into circular platforms for hydrological, nutrient, and climate regeneration, designed to maximize the value of every component in organic waste.
Within this context, the Biomethane Plant in Seville, operated by HEYGAZ, redefines the role of treatment infrastructure in water-stressed regions. Strategically located in the Guadalquivir River Basin, one of the 100 most water-stressed basins globally, as identified by the CEO Water Mandate, this facility processes up to 80,000 tons of wet organic waste per year, primarily from agro-industrial, livestock, and urban sources.
More than 75% of this waste is embedded water, which, in conventional scenarios, would be lost to evaporation (as in open-air composting) or converted into highly polluting leachate (in landfilling). HEYGAZ’s value proposition is clear: to capture, preserve, and repurpose this embedded water through anaerobic digestion in Continuous Stirred Tank Reactors (CSTR), operated under mesophilic or thermophilic conditions, and fully controlled through real-time digital monitoring and SCADA automation.
The outcome is not only clean energy in the form of biogas, but also stabilized liquid digestate, rich in essential nutrients (N, P, K), which is applied as a biofertilizer in nearby agricultural fields. This product replaces synthetic fertilizers, often water-intensive and emission heavy, while restoring soil health and closing agroecological nutrient loops. Every cubic meter of recovered water is fully traceable, from waste intake to final field application, using geographic information systems (GIS), flow sensors, lab analytics, and audit-ready records.
From a corporate sustainability perspective, the project delivers quantifiable water benefits, both in terms of volume and quality, using standardized and robust methodologies:
Under the VWBA 2.0 framework, the A-6 methodology is applied to account for the volume of water embedded in organic waste that is recovered and put to beneficial use.
In parallel, Water Quality Benefit Accounting (WQBA) principles are applied to demonstrate that the system prevents leachate generation, reduces pollutant loads, and safeguards both surface and groundwater bodies.
But this project is more than a technical solution. It reflects a broader vision of territorial regenerative infrastructure, capable of generating tangible, auditable benefits for a wide range of stakeholders: farmers, municipalities, plant operators, rural communities, and regulators. The full traceability of water and the agronomic quality of the digestate allow for more transparent governance, aligned with national water plans, European circular economy regulations, and the Sustainable Development Goals (SDGs 2, 6, 7, 9, 11, 12, 13, 15, and 17).
In short, the Seville Biomethane Plant doesn’t just turn waste into energy, it redefines how we understand and manage the water cycle. It is living proof that smart technology, applied with a sustainability mindset and long-term vision, can transform even the most complex waste streams into scalable, replicable solutions aligned with the challenges of the 21st century.
