The city of Barcelona has plans to create biofuel for its large public transport system; meaning Barcelona buses could soon be running on sewage sludge. Currently, the city’s fleet of 1,100 buses relies heavily on fossil fuels to function, with around 900 buses driving through the streets of Barcelona during rush hour.
The initiative pilot project is part of the Nimbus Project, which receives funding from the European Union. It aims to encourage a circular economy, starting with greener public transport, by producing biomethane, a renewable natural gas, from sewage sludge.
According to the Catalan capital’s main public transport operator, TBM, 70% of its fleet ran on diesel fuel in 2010. By 2020, almost 75% of the buses were hybrid or running on less polluting energy. Even so, it’s still far off the EU’s commitment for over 30% of energy consumption for transport from renewable sources by 2030.
“This is about using bioproducts, which already exist in the atmosphere and giving them a new life,” said TMB depot supervisor Angel Olmo. “Recycling gases that are already in the atmosphere. And if they can be used to power these buses, then it’s the right thing to do”.
The process will work by gathering sewage sludge at water treatment plants. This sludge is generated during the water purifying process,creating biogas. This biogas – made of methane and CO2 – is currently stored in silos and burnt at a later stage to power part of the plant. Once the Nimbus Project is operative in March 2022, CO2 from the biogas will be removed to create biomethane. After being compressed at high pressures, it will be used as fuel for a bus.
One of the plants in the project is the Baix Llobregat wastewater, which manages about half the wastewater from Barcelona’s metropolitan area. The plant receives some 190,000 cubic metres of wastewater during the autumn months. After processing, the water is used for irrigation, cleaning streets and pavements, recharging aquifers and feeding the nearby river.
The project is being run by Cetaqua, a consortium formed by Barcelona’s main water supplier Agbar and TMB. “We are doing this in conjunction with Cetaqua Water Technology Center in order to start this pilot plant that will generate biomethane,” explained Mauri Poch, a strategic developer engineer working at the site. “At first, it will power a single bus. The idea is to use it to power many more in the near future”.
The hope for the project is that when scaled up, this wastewater treatment plant will turn into an “eco-factory”, generating valuable resources instead of waste as a by-product.