Abstract
The European Union’s (EU) climate and energy package requires all EU countries to reduce their greenhouse gas (GHG) emissions by 20% by 2020. Based on current trends, Ireland is on track to miss this target with a projected reduction of only 5% to 6%. The agriculture sector has consistently been the single largest contributor to Irish GHG emissions, representing 33% of all emissions in 2017. Small-scale anaerobic digestion (SSAD) holds promise as an attractive technology for the treatment of livestock manure and the organic fraction of municipal wastes, especially in low population communities or standalone waste treatment facilities. This study assesses the viability of SSAD in Ireland, by modelling the technical, economic, and environmental considerations of operating such plants on commercial Irish dairy farms. The study examines the integration of SSAD on dairy farms with various herd sizes ranging from 50 to 250 dairy cows, with co-digestion afforded by grass grown on available land. Results demonstrate feedstock quantities available on-farm to be sufficient to meet the farm’s energy needs with surplus energy exported, representing between 73% and 79% of the total energy generated. All scenarios investigated demonstrate a net CO2 reduction ranging between 2059–173,237 kg CO2-eq. yr−1. The study found SSAD systems to be profitable within the plant’s lifespan on farms with dairy herds sizes of >100 cows (with payback periods of 8–13 years). The simulated introduction of capital subvention grants similar to other EU countries was seen to significantly lower the plant payback periods. The insights generated from this study show SSAD to be an economically sustainable method for the mitigation of GHG emissions in the Irish agriculture sector.
Highlights
The European Union’s (EU) climate and energy package sets binding greenhouse gas (GHG)emission reduction targets for all EU states by 2020; these include a 20% cut in GHG emissions, to produce 20% of energy consumed from renewable sources, and a 20% improvement in energy efficiency [1]
The farmland available for biogas production increased by just 35.4% between the smallest and largest farm sizes, showing that a larger proportion of farmland is potentially available for biogas production in farms with smaller herd sizes
The methodology undertaken was a “cradle-to-grave” approach to provide an accurate representation of the net CO2- savings for each of the Small-scale anaerobic digestion (SSAD) scenarios per year
Summary
The European Union’s (EU) climate and energy package sets binding greenhouse gas (GHG)emission reduction targets for all EU states by 2020; these include a 20% cut in GHG emissions, to produce 20% of energy consumed from renewable sources, and a 20% improvement in energy efficiency [1]. A promising technology with the capacity to provide both renewable energy and GHG reduction, in the agriculture sector, is anaerobic digestion (AD). AD is a natural process in which microorganisms (hydrolytic, fermentative, acetogenic and methanogenic bacteria) break down biodegradable material in the absence of oxygen, producing biogas (a mixture mainly composed of methane and carbon dioxide) These systems are beneficial for improving on-site energy generation, upgrading wastes, and producing a nutrient-rich fertiliser from the digester effluents. They can reduce pathogenic loads, odours and greenhouse gas emissions emanating from the agricultural processes [5,6,7,8].
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