A b s t r a c t. Digestate from biogas plants can play important role in agriculture by providing nutrients, improving soil structure and reducing the use of mineral fertilizers. Still, less is known about greenhouse gas emissions from soil during and after digestate application. The aim of the study was to estimate the emissions of carbon dioxide (CO 2 ) and methane (CH 4 ) from a field which was fertilized with digestate. The gas fluxes were measured with the eddy covariance system. Each day, the eddy covariance system was installed in various places of the field, depending on the dominant wind direction, so that each time the results were obtained from an area where the digestate was distributed. The results showed the relatively low impact of the studied gases emissions on total greenhouse gas emissions from agriculture. Maximum values of the CO 2 and CH 4 fluxes, 79.62 and 3.049 µmol s -1 m -2
Recently, the greenhouse gas (GHG) emissions from agriculture have received much attention because of the worldwide GHG reduction policy and predicted growing food demand in following years, caused by an increase in population to 9.8 billion in 2050 [UN 2017]. Agriculture contributes 24% to the global GHG emissions [IPCC 2014] and this sector is the largest contributor to the global emissions of non-CO 2 greenhouse gases. Globally increasing food demand may result in ca. 77% rise of GHG related to agriculture, as a consequence not only of the growing livestock population which is expected to induce an increase of emissions from enteric fermentation by 22% in the period from 2005 to 2030 [EPA 2012], or fertilizers usage but also as a result of deforestation and further mechanization [Bajzelj et al. 2014]. Agriculture is responsible for more than 81% of total global anthropogenic nitrous oxide (N 2 O) emissions [Isermann 1994] and 43% of the total anthropogenic methane (CH 4) emissions [Turner et al. 2015]. Enteric fermentation
Circular economy aims to eliminate organic waste through its transformation, composting and processing into other products or energy. The main aim of the study was to determine the specific methane yield (SMY) of anaerobic digestion (AD) of four different fruit and vegetable residues (FVR). In addition, the reduction in greenhouse gas (GHG) emissions was calculated based on the assumption that maize will be replaced by the FVR as a feedstock for biogas production. The SMY of four residues (apple pomace, cabbage leaves, pumpkin peels and fibrous strands and walnut husks) was measured in the biomethane potential test (BMP) in wet anaerobic digestion technology. The highest SMY (297.81 ± 0.65 NL kgVS−1) was observed for cabbage leaves while the lowest SMY (131.07 ± 1.30 kgVS−1) was found for walnut husks. The concentrations of two inhibitory gasses (NH3 and H2S) in biogas were low and did not affect the AD process. Only biogas produced from cabbage leaves was characterised by higher NH3 and H2S concentrations resulting from the highest protein concentration in this waste. FVR used as feedstock in biogas production may decrease the area of maize cultivation. Therefore, the GHG emissions from maize cultivation will be reduced. In Poland only, the use of four studied FVR as feedstock for biogas production would contribute to the reduction of GHG emissions by 43,682 t CO2 eq.
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