Improving quality of manure while reducing emissions
Rich in nutrients such as carbon, nitrogen and sulfur, dairy slurry or manure is a valuable source of organic fertiliser and feedstock for renewable energy. However, during storage it is rapidly degraded by microorganisms producing greenhouse gases (GHG), such as methane and nitrous oxide, alongside other gases, including ammonia and hydrogen sulfide. While all are harmful to the environment and human health, reducing methane would be the fastest way to tackle climate change. According to Aoife McCarthy, coordinator of the EU-funded GasAbate N-plus project, current solutions such as acidification are both potentially hazardous and often energy intensive. McCarthy’s team has developed a solution using a well-studied chemical ingredient proven safe for humans, animals and the environment. GasAbate has consistently achieved an over 80 % reduction in stored manure methane emissions, with over 50 % reductions for ammonia and 80 % for hydrogen sulfide. “We have demonstrated its cost-effectiveness and large-scale manufacture, and after meeting regulatory requirements the product is already on sale in Ireland. We are now in late-stage discussions with several corporate partners for international commercialisation,” says McCarthy.
From laboratory to farm
The GasAbate additive, which inhibits methanogenic microorganisms, is dosed as a liquid into manure storage pits/slurry tanks at specific time intervals and tailored to individual farms, thanks to automated dosing pumps. Targeting methanogens only, the remaining microbiome is unaffected, leaving high-quality organic fertiliser and feedstock for anaerobic digestion to produce biogas for energy. Trials were first carried out on its use in storage tanks containing up to 600 litres of slurry and fitted with flowmeters to monitor biogas production, with biogas composition also monitored. Experimenting with variables such as dosage and application methods, the team achieved emission reductions of 73 % for biogas, 100 % for ammonia and 98 % for hydrogen sulfide. Large-scale commercial dairy farm trials were then carried out with floating chambers on the slurry surface of a tank, and the accumulation of emissions measured over three sample points. “Working with 220 cows, three slurry tanks and 485-590 cubic metres of slurry, we reduced methane production by 80 %,” notes McCarthy.
Boosting biogas
Regarding boosting anaerobic digestion for biogas, the project scaled up testing from a five litre bench-scale reactor to a 270 000 litre commercial-scale reactor. The team achieved a 38 % increase in biogas output with cattle slurry treated with GasAbate, and a 100 % increase in biogas yield with pig slurry at commercial scale. “We also found that GasAbate improved the quality of manure, increasing plant dry matter by 15 % in small-scale pot trials,” adds McCarthy. To satisfy VERA Verification and VDI 4360 biogas standards for the European market, independent trials were run with the Danish Technological Institute, alongside Penn State University trials for the American market.
Eyes on achieving the EU’s climate goals
As stored manure GHG emissions represent around 15 % of all the EU’s agricultural GHG emissions – approximately 1.5 % of the EU’s total – GasAbate could contribute significantly to the EU’s goal of reducing these by at least 55 % by 2030, and towards achieving carbon neutrality by 2050. Additionally, the EU is a signatory to the Global Methane Pledge – a voluntary agreement involving over 150 countries to reduce methane emissions by 30 % from 2020 levels by 2030. “An independent impact assessment of the project using the IdeMat database, modelled a farm with 2 000 cattle, finding that GasAbate would stop 15 000 tonnes of carbon dioxide equivalent being released,” says McCarthy.
Keywords
GasAbate N-plus, manure, slurry, methane, carbon, emissions, greenhouse gas, farm, biogas, dairy, ammonia
