ABSTRACT
Livestock farming has exerted intense environmental pressure on our planet. The high emissions to the environment and the high demands of resources for the production process have encouraged the search for decarbonization and circularity in the livestock sector. In this context, the objective of this study was to evaluate and compare the environmental performance of two different uses for biogas generated in the anaerobic digestion of animal waste, either for electricity generation or biomethane. For this purpose, a life cycle assessment approach was applied to evaluate the potential of anaerobic digestion as a management technology for three different livestock wastes, related to beef cattle, dairy, and sheep in the Brazilian animal production context. The results suggest that the treatment scenarios focusing on biomethane generation were able to mitigate the highest percentage of damages (77 to 108%) in the global warming category when compared to the scenarios without the use of anaerobic digestion (3.00·102 to 3.71·103 kgCO2 eq) or in the perspective of electricity generation (mitigation of 74 to 96%). In terms of freshwater eutrophication, the generation of electricity (- 2.17·10-2 to 2.31·10-3 kg P eq) is more favorable than the purification of biogas to biomethane (- 1.73·10-2 to 2.44·10-3 kg P eq), due to the loss of methane in the upgrading process. In terms of terrestrial ecotoxicity, all scenarios are very similar, with negative values (- 1.19·101 to - 7.17·102 kg 1,4-DCB) due to the benefit of nutrient recovery, especially nitrogen, associated with the use of digestate as fertilizer, which was one of the critical points in all scenarios. Based on these results, it is evident that proper management of all stages of the treatment life cycle is the key to decarbonization and circularity in livestock waste management. The biogas use does not present different effects on the environmental performance of the scenarios studied, demonstrating that the purpose should be chosen according to the needs of each plant or management system.
Subject(s)
Livestock , Waste Management , Cattle , Animals , Sheep , Brazil , Biofuels , Waste Management/methods , Life Cycle Stages , AnaerobiosisABSTRACT
Assessments of soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions are critical for determination of the agricultural practices' potential to mitigate global warming. This study evaluated the photoacoustic spectroscopy (PAS) for the assessment of soil greenhouse gases (GHG) fluxes in comparison to the standard gas chromatography (GC) method. Two long-term experiments with different tillage and cropping systems over a Paleudult were evaluated using static chambers. PAS measurements of CO2 and N2O concentrations showed good relationship and linearity (R2=0.98 and 0.94, respectively) with GC results. However, CH4 measurements were significantly affected by air sample moisture which interfered on CH4 detection by PAS. Overestimation of CO2 and N2O concentrations in air samples determined by PAS (14.6 and 18.7%, respectively) were also related to sampling moisture. CO2 and N2O fluxes showed good agreement between methods (R2=0.96 and 0.95, respectively), though PAS overestimated fluxes by 18.6 and 13.6% in relation to GC results, respectively. PAS showed good sensitivity and was able to detect CO2 and N2O fluxes as low as 332mg CO2 m-2 h-1 and 21µg N2O m-2 h-1. PAS analyzer should be detailed calibrated to reduce humidity interference on CO2, CH4 and N2O concentrations measurements avoiding overestimation or erroneous determination of soil GHG fluxes.
As avaliações das emissões de dióxido de carbono (CO2), metano (CH4) e óxido nitroso (N2O) do solo são fundamentais para a determinação do potencial de práticas agrícolas em mitigar o aquecimento global. Este estudo avaliou a espectroscopia fotoacústica (EFA) para a determinação dos fluxos de gases de efeito estufa (GEE) do solo em comparação com o método padrão de cromatografia gasosa (CG). Dois experimentos de longa duração com diferentes sistemas de preparo do solo e rotação de culturas sobre um Argissolo foram avaliados usando câmaras estáticas. As medidas das concentrações de CO2 e N2O realizadas por EFA mostraram boa correlação e linearidade (R2=0,98 e 0,94; respectivamente) com os resultados de CG. Entretanto, as medidas de CH4 foram significativamente afetadas pela umidade da amostra de ar que interferiu na detecção do CH4 por EFA. A superestimativa das concentrações de CO2 e N2O nas amostras analisadas por EFA (14,6 e 18,7%; respectivamente) também foram relacionadas com o conteúdo de umidade da amostra. Os fluxos de CO2 e N2O mostraram boa correlação entre os métodos (R2=0,96 e 0,95; respectivamente), apesar da superestimativa dos fluxos determinados por EFA ter sido de 18,6 e 13,6% em relação aos resultados obtidos por CG, respectivamente. A EFA mostrou boa sensibilidade e foi capaz de detectar fluxos de CO2 e N2O tão baixos quanto 332mg CO2 m-2 h-1 and 21µg N2O m-2 h-1. A calibração detalhada do analisador fotoacústico para reduzir a interferência da umidade das amostras nas medidas das concentrações de CO2, CH4 e N2O deve ser realizada a fim de evitar superestimativa ou erro na determinação dos fluxos de GEE do solo.
