Balancing the Use of Crop Residues for Biofuels with Impacts on Soil and Greenhouse Gases

by Jessica Bass

The use of crop residues as a second-generation source of biofuels may hold potential to help the United States fulfill its 2022 goal production quota outlined in the 2007 Energy Independence and Security Act. Yet, this annual accumulation plays an important role toward maintaining soil organic carbon (SOC) stocks and reducing soil erosion, protecting field health to sustain year-after-year of yields. Adler et al. (2015) use the DayCent biogeochemical model to analyze the costs and benefits of crop residue removal and use based upon its impact on crop yield, SOC content, and N2O emissions, over the course of twenty years. They examined these relationships with respect to a variety of anticipated treatment options, including: a baseline condition with no residue removal, a sample of 50% residue removal without any replacements, 50% residue removal with a nitrogen replacement equivalent to the amount removed, and a 50% residue removal and equivalent application of a high-lignin fermentation byproduct (HLFB). Continue reading

Shale Gas Produces Half the GHG Emissions and Consumes Half the Freshwater of Coal

by Shannon Julius

The long term environmental concerns having to do with shale gas development are primarily greenhouse gas (GHG) emissions and freshwater consumption, as other forms of environmental degradation can be remediated over time. Ian Laurenzi and Jersey Gilbert (2013) of the ExxonMobile Research and Engineering Company performed a life cycle assessment (LCA) of both GHG emissions and freshwater consumption of Marcellus shale gas. The life cycle begins with well drilling and ends with burning the fuel for power generation. Using their elaborated system boundaries, the researchers found that a Marcellus shale gas well releases 466 kg of carbon equivalent units per megawatt hour of power produced (kg CO2eq/MWh) and consumes 224 gallons of freshwater per megawatt hour of power produced (gal/MWh) over the course of its lifetime. The biggest contributor to both GHG emissions and freshwater consumption is power generation. The result of this study are highly dependent on the variables chosen to represent the shale gas well life cycle, especially the expected ultimate recovery of natural gas. Despite the potential for variability of results, the result of 466 CO2eq/MWh is consistent with other published life cycle assessments for conventional and shale gas, and almost all of the 14 other studies fall within the 10%–90% range of 450–567 CO2eq/MWh. Even considering factors that can increase total results, this study shows that average GHG emissions from shale gas are 53% lower and freshwater consumption is 50% lower than what is required for an average coal life cycle. Continue reading