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Biogas climate benefit greater than previously thought

18 February 2010 Expertsvar

Biogas from refuse produces 95 per cent less greenhouse gas emissions than petrol, according to a new research report. With a few simple improvements to the biogas plants, the figure can rise to 120 per cent – i.e. biogas becomes more than climate neutral. This can be compared with the standard figures used today, which indicate that biogas produces 80 per cent lower emissions than petrol.

A research group at the Lund University has calculated the figures on behalf of the Swedish Energy Agency after having analysed a biogas plant in Skåne. The case study will make it easier to study and optimise other biogas facilities. In Sweden there are some 20 similar plants, producing biogas for use in cars and other vehicles. As much vehicle gas is produced by sewage treatment works that produce biogas from sewage sludge.

“The plant we have studied is fairly representative of an average biogas plant that processes waste and manure. In our study we have calculated emissions for the entire production chain and included both direct and indirect emissions. What is particular to our study is that we have included indirect factors that have not previously been taken into account, for example how the ground is affected when mineral fertiliser is replaced with bio-fertiliser. In addition, methane leaching from the plant is measured and not based on standard data that is often otherwise used in this kind of analysis”, points out Mikael Lantz, doctoral student in Environmental and Energy Systems Studies at Lund University.

The researchers also observed that the biogas releases 16 gram/kWh biogas of the greenhouse gases methane, laughing gas and carbon dioxide. These emissions are around 95 per cent lower than from petrol and significantly better than the standard values used today.

In order to make the biogas even more climate-friendly, the researchers propose that the plants should be heated using wood chips, which could also be cheaper for the biogas producer.

“Another suggestion is to cover the bio-fertiliser stores to reduce the losses of nitrogen and reduce dilution with rain water. The plant has already implemented this measure. By using a few other recommendations as well, the emissions can be reduced to 120 per cent lower than petrol, without increasing the production costs by more than a couple of öre per kWh of vehicle gas”, explains Mikael Lantz.

Today over 23 000 vehicles in Sweden drive on biogas.

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