A couple of stories caught my eye this week. The first, in the US Sewage Could Provide Fuel of the Future. The second, in the UK sewage is providing the fuel of the present. OK, so that isn’t really a fair comparison as the fuel of use is not the same in each case. In the US they are talking about hydrogen and in the UK methane. What links them though is the underlying process: anaerobic digestion. This process takes biodegradeable wastes and uses bacteria to break down, consume and so reduce the amount of solid waste that needs to be disposed of. As a byproduct of this process, biogas is produced. Biogas is typically 60% methane and 40% carbon dioxide and has mostly been used in the past for onsite combined heat and power production. The resulting heat and electricity is then used to reduce the energy demand of the waste treatment process.
Where the stories diverge is in the utilisation of the biogas produced. To produce the fuel for Geneco’s bio-bus in the UK, the biogas is ‘cleaned-up’. This means that the carbon dioxide is removed and a small amount of propane added to the gas to produce a suitable transport fuel. This isn’t the whole story in the UK, at their Avonmouth plant this cleaned-up or upgraded biogas is also being injected into the national gas grid making it available to consumers to use to heat their homes or cook food beginning the process of greening the gas grid.
In the US the biogas is being utilised in a 300 kW molten carbonate fuel cell (MCFC) to produce heat, power, and hydrogen. It’s the hydrogen that is the fuel of the future of the headline. The hydrogen generated at the US plant will be compressed and used to fill up fuel cell powered vehicles (FCVs) at an onsite public hydrogen refueling station. But when will this future be? It could be closer than you think as Toyota plan to launch their new FCV, the Mirai, to the public next year.
Senior Lecturer in Renewable Energy
Sustainable Environment Research Centre
University of South Wales