Processing farming waste through anaerobic digestion

Agriculture accounts for around 24% of Scotland’s greenhouse gas emissions, of which methane accounts for around 44%. A significant proportion results from generation of manure and slurries in livestock production.

Anaerobic digestion is a biological process that generates a methane-rich biogas from resources such as manure and food waste. When carried out under controlled conditions, the biogas can be captured and converted to energy for heat and electricity.

The Scottish Government has recognised the potential for farmyard slurry to contribute to renewable and bioenergy ambitions. The 2021 Bioenergy Update recognised a need to examine the potential for a Scottish market for digestate – the nutrient-rich material produced by anaerobic digestion, which can be a good fertiliser. Having a market for digestate would remove constraints on greater production of biomethane.

This report examines the potential to reduce emissions by processing agricultural wastes through anaerobic digestion plants. The focus is on agricultural wastes that consist mainly of animal manures and slurries, which are highly underutilised resources.

Conclusions

• Anaerobic digestion is an important tool in the fight against climate change. However, manures and slurries do not yield high volumes of biogas and the latter typically has a low dry matter content. This means it is uneconomical to transport it to the large-scale AD plants that currently exist.
• On-farm plants are particularly suitable for farms generating liquid slurries throughout the year, such as dairy farms. Such plants can therefore operate all year round to produce biogas and/or electricity consistently.
• Manure and slurry-only farm-scale solutions are available, but there has been little uptake in recent years as policies have driven economies of scale. Although solutions exist, there is low visibility of farms running, in a profitable way, easy-to-operate micro-scale solutions that would be appropriate for individual farms.

For further information, including the findings, please download the report.

If you require the report in an alternative format such as a Word document, please contact info@climatexchange.org.uk or 0131 651 4783.