Anaerobic Digestion as a Tool to Mitigate Greenhouse Gas Emissions from Animal Slurries

Abstract

Anaerobic Digestion (AD) has been gaining popularity in the last decades for the production of biogas from organic waste, agricultural waste, and energy crops. Biogas is a mixture of approximately 70 % methane, 29 % carbon dioxide, and 1 % other gases. Biogas plants produce electrical and thermal energy by burning the biogas in combined heat and power units or upgrade the biogas into a 95 % to 99 % pure biomethane, which can then be injected into the grid or used as a transport fuel. A wet mixture called digestate is left after biogas production. The digestate is a great fertiliser since it contains all nutrients and micronutrients for needed for agriculture such as potassium, phosphorus, and nitrogen. Ireland is distinguished by the European Commission as the country with the largest biomethane potential in Europe. The Irish Biogas Association states that biogas produced using AD technology should be at the core of Ireland’s future energy mix. In Ireland, the animal slurry is currently being stored in open tanks, emitting greenhouse gas emissions. Each particle of methane is 25 times more harmful than a particle of carbon dioxide. By 2022, Ireland’s livestock includes more than 7 million cows, 1.7 million pigs, and 16.5 million poultry per year. In this study, we propose modelling the retrofitting of existing open slurry tanks into covered lagoons to harvest the biogas from the animal slurries to reduce greenhouse emissions. The digestate will be utilised as fertiliser to enhance soil health, crop yield, and productivity. Based on average herd sizes and daily slurry availability, optimal covered lagoon dimensions will be found. A global value will be obtained for the biogas potential from animal slurries in Ireland.