Background

The biofactory initiative in Guijuelo, Salamanca, Spain, focuses on transforming wastewater and agri-food industrial by-products into valuable resources. The project addresses the high environmental and economic costs of bio-waste management, the need for circular economy integration in wastewater treatment, and the demand for alternative biofuels and renewable energy solutions. 

Approach

The initiative employs anaerobic co-digestion of sewage sludge with agri-food industrial waste to enhance biogas production. Through ABAD Bioenergy® purification technology, biogas is upgraded to biomethane for use as a renewable fuel. Thermal hydrolysis is applied to precondition biowaste for improved digestion efficiency, while electrostimulated anaerobic bioreactors (ELSAR®) facilitate biohydrogen generation. Additionally, wastewater treatment residues are repurposed for bioplastic and biofertilizer production, supporting a circular bioeconomy.

Stakeholders involved include Aqualia, the Salamanca Municipality, the local pork industry, and the Spanish Biomass Association (AVEBIOM). Implementation steps involved integrating existing wastewater treatment infrastructure into biofactory operations, establishing anaerobic co-digestion processes, optimizing biogas and biomethane production, and developing compressed bio-CNG storage and distribution systems. Furthermore, applications for recovered resources, such as fertilizers, bioplastics, and alternative fuels, were expanded.

Outcomes and impacts

The biofactory has achieved significant environmental and economic benefits. The biomethane production capacity has reached 10 Nm³/h, and optimized co-digestion has led to increased biogas production. Additionally, CO₂ emissions have been significantly reduced by replacing fossil fuels with bio-CNG in municipal and industrial vehicles. In addition, the initiative has eliminated the dependency of local food industries on a single waste manager, reduced waste management costs, and increased knowledge among partners about enhanced sewage treatment plant operations. The diversification of energy sources within the treatment plant has further strengthened the project’s sustainability. Notably, the initiative received recognition at the 2021 AVEBIOM Innovation Awards as one of the leading renewable gas recovery projects.

Lessons learned

The initiative successfully transformed a traditional wastewater treatment plant into a fully functional biofactory, establishing synergies with local industries and developing a financially viable circular bioeconomy model. However, challenges remain, including the scalability of biogas and biomethane production, regulatory barriers for grid injection of renewable gases, and logistical complexities in bio-waste collection for large-scale anaerobic co-digestion. Despite these challenges, the biofactory model has potential for replication in regions with significant organic waste production and municipal wastewater treatment plants worldwide. Supported by the Salamanca Living Lab, future research and innovation will further enhance the scalability and effectiveness of bio-waste recovery technologies.