Sustainable Biomass Resources for Biogas Production: Mapping and Analysis of the Potential for Sustainable Biomass Utilization in Denmark and Europe

The aim of this thesis was to identify and map sustainable biomass resources, which can be utilised for biogas production with minimal negative impacts on the environment, nature and climate. Furthermore, the aim of this thesis was to assess the resource potential and feasibility of utilising such biomasses in the biogas sector. Sustainability in the use of biomass feedstock for energy production is of key importance for a stable future food and energy supply, and for the functionality of the Earths ecosystems.

A range of biomass resources were assessed in respect to sustainability, availability, and energetic feasibility by combining the use of a geographical information system with laboratory experiments, statistical analyses, field studies, and literature reviews. The biomasses identified as sustainable in this study were animal manure, straw, surplus grass from agricultural production, grass from nature conservation, and grass from roadside verges.

It was found that a significant potential of the investigated sustainable biomass resources are available in Denmark, but also on European level. In Europe, the energy potential in 2030 from animal manure, straw and surplus grass was projected to range from 39.3-66.9 Mtoe, depending on the availability of the residues.

Grass from roadside verges and meadow habitats in Denmark represent two currently unutilised sources. If utilised in the Danish biogas sector, the results showed that the resources represent a net energy potential of 60,000 -122,000 GJ and 640,000 GJ respectively. The energy return on energy investment when utilising roadside grass were estimated to range from 2.17 to 2.88, while 1.7 to 3.3 for the use of meadow grass. It was found that the concept of utilising grasses from nature habitats and roadside verges can function as a provider of renewable energy, a method for increasing the biodiversity of the nature habitats and roadside verges, and as a method for redistributing nutrients to the agricultural land.

In the Region of Southern Denmark, an excess production of grass was estimated for several of the municipalities but the excess production was found to be quite sensitive to the management practice of the grass fields and the productivity of the grass. The estimated yields were found to be sufficient to serve as sole co-substrate in 2-16 biogas plants with a capacity of 200.000 t biomass annually.

Based on the results it was concluded that deteriorating and overuse of the ecosystems, as well as substitution of food and feed production does not have to be a precondition for bioenergy production. On the contrary, positive externalities from well managed bioenergy production systems can contribute in reducing environmental problems, and prevent the loss of biodiversity without conflicting the food and feed supply.