Alternative use of grassland biomass for biorefinery in Ireland: a scoping study

The need to reduce greenhouse gas emissions and dependency on fossil fuels has been one of the main driving forces to use renewable resources for energy and chemicals. The integrated use of grassland biomass for the production of chemicals and energy, also known as Green Biorefinery (GBR), has received much attention and several European countries have developed GBR systems, including Austria, Denmark and Germany. In Ireland, approximately 90% of the 4.3 million hectares used for agriculture is under grassland and used in livestock production systems. Recently livestock numbers have declined and a surplus of grass biomass is predicted. GBR has potential to provide supplementary income from this surplus grass. As part of a scoping study, I assessed the economic, technical and environmental feasibility of a GBR in an Irish context, and developed a blueprint for a first generation GBR.
Scenario analyses suggested that the ideal catchment area for a GBR was 700-800 ha depending on biomass availability within the catchment area, and the availability should be in excess of 30% in order to contain transport costs. An added benefit of a decentralised GBR facility processing approx. 0.8 t of dry matter per hour is that it allows for ease of operation, and better knowledge of the source and quality of the herbage being supplied.
The viability of a GBR will be highest in areas which experience declining numbers of livestock and lower farm income, particularly. This mainly, but not exclusively, occurs in areas with many beef farms. These areas have a high potential availability of surplus grass biomass and in such a situation the GBR would not have to compete with traditional agricultural commodities, but rather would provide potential supplementary income to farmers.
The transitional development of a GBR system is likely to be most successful if current harvesting practices (i.e. a two-cut silage system) are adopted. The quality of the biomass from such a harvesting system is compatible with the basic GBR technologies used to produce insulation materials and proteinaceous products for animal feed. In the longer-term, higher value products could be produced by retro-fitting the GBR facility. Analyses also showed that feedstock quality can be best controlled by operating a silage-only system, with on-site ensiling of the grass material at the GBR facility. The use of silage as a feedstock also facilitates year-round operation of the GBR facility.
Biorefinery processes are energy intensive. Therefore, the viability of the GBR largely depends on self–sufficiency for energy. This can be achieved by anaerobic digestion of the fibre slurries that remain after processing.
The residual material remaining after the anaerobic digestion can be used as fertiliser on the farm supplying the biomass, as part of a “waste management strategy” that aims to maintain nutrient balance between the GBR and the source farms. This recycling will reduce direct costs of the supplying farms.
The blueprint outlined in this thesis provides a framework for the development of a first generation GBR. The blueprint has also identified key areas that require further research: improved ensiling techniques, integration of livestock farming systems and GBR systems, and nutrient budgeting of the GBR system.