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Manure treatment such as anaerobic digestion and solid-liquid separation has shown a potential to abate greenhouse gas (GHG) emissions, but few studies have considered GHG emissions from both storage and field application regarding crop yield. In this study, four different organic fertilizers were studied: untreated cattle manure (CA); digestate of cattle manure anaerobically co-digested with grass-clover (DD); a liquid fraction from the separation of DD (LF); and a liquid fraction derived from a biogas desulfurization biofilter enriched with sulfur and ammonium (NS). The CH4, N2O and NH3 emissions during storage of CA, DD and LF between August and November 2020 (11 weeks) were quantified. Storage continued until April 2021 when these materials, as well as the NS fertilizer and a mineral NKS fertilizer, were applied at a rate of 100 kg total N/ ha to spring barley. N2O emissions and soil mineral N content were monitored during the growing season. Overall, CH4 emissions during storage were the main source of GHG emissions independent of treatments, accounting for 85 %, 40 % and 11 % of total GHG emissions (based on field application of 100 kg/ ha total N) from treatments CA, DD and LF, respectively. Anaerobic digestion and separation significantly reduced CH4 emissions during storage due to the diminished content of degradable organic matter available for methanogens. The N2O emissions from treatments CA, DD, and LF during storage were not significantly different. Treatments DD and LF emitted more NH3 than CA during storage, presumably because of higher pH and ammonium content. In the field experiment, the dilute solution of NS emitted the most N2O, while emissions from treatments CA, DD and LF were comparable. Yield-scaled GHG emissions for treatments CA, DD, LF and NS during both periods of storage and field were 44.4, 17.1, 8.5 and 24.3 kg CO2 eq/ hkg grain yield, respectively. Anaerobic digestion with or without separation were thus effective strategies for the m

• Clover grass as a co-substrate in biogas production is an important source of biogenic nitrogen contributing to carbon sequestration and biodiversity • Anaerobic digestion has a high potential for reduction of GHG emissions • High nitrogen efficiency of ammonia-rich fractions • Dried fiber fraction immobilizes nitrogen but is usable as phosphorus source for legume crops

For at producere mere effektive gødninger til økologisk produktion blev kløvergræs og kvæggylle brugt til at producere forskellige organiske gødningstyper samt biogas ved anvendelse af forskellige efterbehandlingsteknologier. Ideen bag var at øge mængden af plantetilgængeligt kvælstof (N) i gødningen og reducere emissionerne. Resultaterne viste en positiv effekt på gødningens klimapåvirkning sammenlignet med ubehandlet gylle, på grund af reducerede metanemissioner fra opbevaring af gylle og den producerede biogas, der kan erstatte fossile brændstoffer.

For at producere mere effektive gødninger til økologisk produktion blev kløvergræs og kvæggylle brugt til at producere forskellige organiske gødningstyper samt biogas ved anvendelse af forskellige efterbehandlingsteknologier. Husdyrgødning kan bruges direkte på marken som gødning. Alternativt kan husdyrgødningen afgasses i et biogasanlæg og den afgassede biomasse kan så bruges på marken som gødning. Et andet alternativ er gå videre med forarbejdningen og separere den afgassede biomasse i en flydende og fast fraktion, der så kan bruges som gødning på marken og derudover via en stripning af den faste fraktion og svovl fra biogasprocessen producere en NS-gødning. Disse forskellige gødningstyper har forskellige kemiske og fysiske egenskaber, hvilket kan påvirke drivhusgasemissionerne under forarbejdning, opbevaring og anvendelse på marken. I ClimOptic-projektet blev gødningerne fremstillet og brugt i et markforsøg med vårbyg, hvor emissioner under lagring og i marken blev målt. Livscyklusvurdering (LCA) blev brugt som metode for at undersøge klimaeffekten af at producere og bruge de forskellige gødningstyper fremfor at bruge husdyrgødningen direkte eller bruge det afgassede biomasse før separering til gødning. Klimaaftrykket af I) de producerede gødningstyper (kg CO2e per 100 kg total N) og II) vårbyg produceret med de forskellige gødningstyper (kg CO2e per t tørstof vårbyg) blev estimeret. Resultaterne viste overordnet en positiv effekt på gødningens klimapåvirkning sammenlignet med ubehandlet gylle, primært på grund af reducerede emissioner fra opbevaring af gylle og genanvendt biogas fra behandlingerne, der kan erstatte fossile brændstoffer. Klimaaftrykket af 100 kg total N i de forskellige gødningstyper viste en reduktion på 75-87%, når ubehandlet kvæggylle blev erstattet med afgasset biomasse eller mere forarbejdede gødningsprodukter. Den primære årsag til de reducerede klimaaftryk i de behandlede gødningstyper sammenlignet med ubehandlet kvæggylle er de reducerede

Anaerobic digestion is a widely used method for treating liquid manure (slurry) and other biomasses, producing biogas as a renewable energy source for heating and electricity generation. The digestate from the biogas plant can be further processed to produce alternative organic fertilizers and enhance nutrient recycling, but the impact of digestate post-treatment on the environment needs to be further investigated. In this study, using a life cycle assessment approach, we explored how fertilizers derived from cattle slurry and grass-clover co-digestion treatment (digestate, solid and liquid fractions from digestate separation, and an enriched liquid nitrogen-sulfur product derived from post-processing of biogas and drying of the solid fraction) may influence the greenhouse gas (GHG) balance compared to the baseline scenario with untreated cattle slurry. To perform this analysis, results from experiments were used together with data from existing literature and databases. The chosen functional units were I) 100 kg of total nitrogen in the final organic fertilizer and II) 1 ton of spring barley dry matter (DM). The respective system boundaries were cradle-to-processing gate and cradle-to-field application, respectively. The global warming potential (GWP) of production and storage of the alternative organic fertilizers were 13 to 25% of the baseline scenario. When considering the second functional unit, the carbon footprint were 25 to 140% of the baseline scenario. The main hotspots in the carbon footprint of the fertilizers were GHG emissions from storage and field application of the organic fertilizers, and production of the grass-clover, whereas the biogas produced by anaerobic digestion greatly reduced the GWP. The present study shows that there is significant potential for climate impact mitigation in the replacement of untreated slurry with alternative fertilizers derived from anaerobic digestion, mainly due to reduced emissions during storage, and the production

Not applicable (oral presentation)

Anaerobic digestion is an environmental technology that not only produces biogas to substitute fossil fuel, but also digestate that can serve as organic fertilizer. In this project, post-digestion treatment processes produced new fertilizer materials with contrasting characteristics. The nitrogen use efficiency and nutrient value to crops, and environmental impacts such as GHG emissions, of both traditional and post-digestion products were studied to find solutions towards sustainable agriculture. The study quantifies 1) emissions of N2O, CH4, CO2 and NH3 from untreated manure and digestate products during storage and N2O emissions after field application, 2) yield performance and N use efficiency; and 3) overall greenhouse gas emissions intensity of manure and digestate products at field and farm level. Digestate products showed 70-90% less CH4 emissions during 11 weeks of storage compared to untreated manure, though higher potential for NH3 losses. Since CH4 emission during storage is the largest component of the GHG balance for both untreated manure and digestates (Baral et al., 2018), the processing of digestates looks promising as strategy for GHG mitigation. The field study will demonstrate if the new treatment technologies also show improvements in N use efficiency. Given that no synthetic chemicals are involved in digestate procesing, the strategy is potentially available to organic farms, where N is typically limiting productivity. Biogas technologies depend on subsidies to compete with fossil fuel, but compared with other GHG mitigation options for agriculture, strategies based on biogas treatment may be cost-effective.