From sewage to steering wheel: the Nimbus bus project in Barcelona

Nimbus project: how does it work?

The vehicle, known as Nimbus, travels an average of 14,000 kilometers per year without using a single drop of conventional fuel. Nimbus has been in operation for five years and is the result of a collaboration between Aigües de Barcelona, Transports Metropolitans de Barcelona (TMB), the Autonomous University of Barcelona (UAB), and the technology center Cetaqua.

Researchers from Veolo, in collaboration with TMB and the Autonomous University of Barcelona, developed the project using a large treatment plant capable of processing 400,000 m³ of wastewater daily. After five years of work, they succeeded in producing a biofuel that emits 80% less CO₂ than natural gas.

The process transforms sludge into biomethane, allowing the V3 bus line to travel up to 100 kilometers a day. The resulting biogas contains about 65% methane and 35% CO₂, which is then purified and enhanced by adding hydrogen from renewable sources, reaching a high methane concentration suitable for distribution networks or gas-powered vehicles. Additionally, the process produces no unpleasant odors and significantly reduces emissions.

As a result, the biomethane used in the V3 line complies with the Euro VI emissions standards set by the European Union. The Nimbus project, with a budget of over 11 million euros, aims to meet the transportation needs of Barcelona’s peripheral areas, where electric buses are still not effective due to their limited passenger capacity and range.