Dr. Ciara Beausang:

I thank the Chair and the committee for the opportunity to present today. I am a research scientist in the field of environmental sustainability. I undertook my PhD in University College Dublin, where I examined the environmental impact of implementing anaerobic digestion in Ireland. All views contained within this statement are mine alone and do not necessarily reflect those of my wider researcher colleagues or associated organisations. My comments today will focus on the key issues relating to the environmental impacts of biogas production in Ireland. This research has been published in international peer-reviewed journals and is openly available.

Often when the environmental sustainability of biogas is discussed, it is in the context of greenhouse gas mitigation. However, there is now a consensus that biogas production itself may result in greenhouse gas emissions. It is important therefore that this risk is assessed in determining the overall policy approach. One of the most important factors to consider is the raw material from which the biogas will be produced. In Ireland, the most readily available resource for biogas is grass silage, as outlined in reports from the Sustainable Energy Authority of Ireland and Gas Networks Ireland. Co-digestion of grass silage with animal manures such as cattle slurry is likely to be the main way biogas is produced nationally. There is a risk that using high shares of grass silage may have negative environmental impacts. The conventional thinking was that additional grass silage for biogas could be produced by increasing fertiliser application. However, in my research I modelled the environmental impacts of digesting different proportions of grass silage and cattle slurry for biogas production and found that using high shares of grass silage may have negative environmental impacts. While this approach avoids competition with feed production, the results showed that this can lead to an increase in greenhouse gas emissions when higher proportions of grass silage are digested due to the additional fertiliser that is required. The impact arises from both the production of the fertiliser itself and the emissions that are released when it is spread on land. As a result, alternative approaches need to be considered to provide surplus grass silage without relying on additional inorganic nitrogen fertiliser. Preliminary research by Teagasc has shown that incorporating legumes such as red clover or the use of multi-species swards has the potential to increase yields without the addition of inorganic nitrogen. This would improve the sustainability of biogas produced from silage and should be promoted, provided that other potential impacts, such as carbon loss and herbicide use during reseeding, are minimised.

The second issue I want to raise is methane leakage from biogas plants. The main component of biogas is methane, which is a powerful shortlived climate pollutant. When methane leakages occur due to increased biogas production, these can contribute to global warming and reduce the environmental benefits. Quantifying methane emissions from biogas plants is becoming a significant topic of interest for the scientific community. The rate of methane loss assumed in life-cycle assessments of biogas is relatively conservative, with many studies assuming a loss of 1% by default. In my research, I used a value of 2.4%, which was the average rate of emissions for 13 agricultural biogas plants in Denmark. As methane loss may be the largest contributor to the carbon footprint of biogas production, it would be important that biogas plants in Ireland monitor, report and address methane losses.

Finally, there is a potential risk of burden shifting occurring if other environmental impacts are not taken into account. The material remaining after anaerobic digestion is known as digestate and can be used as a fertiliser. Digestate has been shown to have higher levels of ammonium compared with the organic substrate going into the AD process. As a result, there is a risk of increased environmental impacts from acidification due to the emissions from digestate application. This is a concern, especially as Ireland continues to breach its emissions target for ammonia under the national emissions ceilings directive. Appropriate digestate management will be critical, including the use of low-emission slurry spreading, LESS, for digestate application.

The scientific research suggests that we need to promote a cascading use of biological resources in the bioeconomy. The research project, Biorefinery Glas, has demonstrated the potential of biorefining to create a variety of products from freshly harvested grass. These products include feed for animals and the remaining grass whey can be used for biogas production. This approach can improve sustainability through diversification into the bioeconomy and makes the best use of environmental resources.