The use of biomethane as a fuel for urban public transport in Barcelona is now a reality, thanks to the European LIFE NIMBUS project. Over the past five years, this pioneering initiative has demonstrated the feasibility of producing biomethane from sewage sludge and power-to-gas technologies – that is, technologies which harness surplus renewable energy, converting it first into hydrogen and then into biomethane.
The process, implemented at the Baix Llobregat Wastewater Treatment Plant (WWTP) managed by Aigües de Barcelona, has resulted in the supply of biomethane to NIMBUS, a pilot bus operated by Transports Metropolitans de Barcelona (TMB). This bus is capable of covering more than 14,000 kilometres per year using biomethane, thereby reducing its annual CO2 emissions by 28 tonnes and lowering its carbon footprint by over 80%.
These results were presented at the project’s final event held in Barcelona, in which LIFE NIMBUS was showcased as a tangible and effective circular solution to advance the decarbonisation of the urban fleet. Alessandro Solimeno, Project Manager and Researcher at Cetaqua–Water Technology Centre, emphasised that LIFE NIMBUS “demonstrates that it is possible to sustainably produce high-quality biomethane by recovering wastewater treatment residues such as digested sludge.”
LIFE NIMBUS, co-funded by the European Union’s LIFE programme and coordinated by Cetaqua–Water Technology Centre with the participation of Aigües de Barcelona, TMB, and the Universitat Autònoma de Barcelona (UAB), represents a starting point for exploring large-scale biomethane production at wastewater treatment plants.
In this regard, Joana Tobella, Director of Innovation at Aigües de Barcelona, stated that “we need large-scale innovation projects such as LIFE NIMBUS to build trust among our stakeholders and ensure their support in scaling up models and processes that contribute to the sustainability of our operations.”
Additionally, Albert Guisasola, Professor in the Department of Chemical, Biological and Environmental Engineering at the Universitat Autònoma de Barcelona (UAB) — the organisation responsible for hydrogen production through biological systems, which are significantly more sustainable than conventional methods — believes that the LIFE NIMBUS technology “can be easily replicated and scaled up at other wastewater treatment plants (WWTPs), thus multiplying biomethane production sustainably through the recovery of waste.”
In Europe, the transport sector accounts for around 30% of total energy consumption. However, less than 10% of the fuels used in transport are currently renewable. In response, the European Union aims to raise this share to over 30% by 2030.
According to Mario Canet, Head of Bus Innovation and Projects at TMB, “LIFE NIMBUS has provided valuable insights into how to decarbonise Barcelona’s bus fleet”, and he believes the project’s impact goes even further: “the technology developed could have a major impact not only on urban transport, but also on freight transport.”
LIFE NIMBUS is aligned with Spain’s Biogas Roadmap, approved in 2022, which identifies the main challenges and opportunities for the development of this renewable gas and sets out plans to quadruple national production by 2030.