The Total Picture: The Benefits of a Switchgrass Biorefinery System after Analysis using the Life Cycle Assessment

Switchgrass (Panicum virgatum) is a type of prairie grass that has been proposed as a valuable crop for bioenergy, bioethanol, and biochemical (phenol) manufacturing (Cherubini and Jungmeier, 2009). The grass’s attractiveness arises from its minimal nutrient intake, its high overall energy production, its habitat diversity, and its ability to sequester carbon. Biomass energy has been considered most efficient while using a biorefinery approach in which multiple technological approaches are used conjointly.— Alec Faggen
Cherubini, F., Jungmeier, G., 2009. LCA of a biorefinery concept producing bioethanol, bioenergy, and chemicals from switchgrass. The International Journal of Life Cycle Assessment 15, 5366.

Cherubini and Jungmeier working at the Norwegian University of Science and Technology and at the Institute of Energy Research used a Life Cycle Assessment (LCA) methodology to compare a biorefinery system to a fossil reference system. The biorefinery approach used switchgrass to produce bioethanol (instead of gasoline), heat from biomethane (instead of natural gas), electricity, heat, and phenols. The LCA calculates the total magnitude of contributions from all inputs and outputs throughout production. The authors were especially focused on green house gas (GHG) emissions and fossil energy usage because high demands for sustainable energy and climate change mitigation are the primary dictators of biorefinery progression.
     The biorefinery technique of switchgrass decreased GHG emissions by 79% and saved about 80% of non-renewable energy. The energy output of the system is 3.6 times the non-renewable energy input. During the first 20 years, the soil sequesters a large amount of atmospheric carbon before it reaches a new equilibrium. These years contribute heavily to the decrease in GHG emissions for both carbon dioxide and methane. After these first years, the GHG emissions were produced mainly from switchgrass pellet production (85%). The biorefinery system also decreased all other investigated environmental impacts during the first 20 years, except for the impacts in the areas of acidification and eutrophication which increased.
Nitrous oxide (N2O) has a 298 times greater global warming potential than carbon dioxide, making N2O an important variable to study in terms of nitrogen fertilizer use and organic matter decomposition in soil. Although the biorefinery system released more N2O into the atmosphere, the emissions varied considerably depending on variables such as soil type, climate, and tillage methods. 

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