Dartmouth Events

Committee: Lee Lynd (chair), Caitlin Hicks Pries, Mark Laser, Armen Kemanian from Penn State University

Abstract:

In the majority of the IPCC’s scenarios for keeping global climate change to a 1.5℃ temperature increase, bioenergy plays a larger role than both wind and solar in the future global energy supply. Specifically, 2^nd generation (2G) biofuels have been identified as an important to actualize, large impact negative emission technology to be deployed on a global scale. Their potential as a negative emission technology relies on the perpetuity of growing 2G feedstocks on an agricultural field, an assumption that is inherently flawed. Though 2G biofuel production utilizes non-edible feedstocks such as agricultural residues to produce liquid fuel, harvesting crop residues is not a sustainable practice without considerable management of the soil underneath. By harvesting excessive crop residues from the field, soil health can diminish and critically, the carbon sequestered in the soils of agricultural fields can decrease. Currently, in the most popular process models published by the National Renewable Energy Laboratory (NREL), this potential for soil degradation is unaddressed. However, through collaboration with various producers of 2G biofuels including at NREL, we have identified an opportunity embedded within the 2G biofuel production pathway to solve the soil health dilemma and increase the viability of biofuel production in a low carbon economy. Through our study, we have collected evidence to suggest that biofuel production accompanied by return of its byproduct to the soil can result in increased amounts of carbon stored underground even when compared to a business-as-usual case of non-biofuel production. Our study experimentally and theoretically evaluates the carbon retention potential of various 2G biofuel byproducts and related bioprocessed material and compares them to the business-as-usual case. Through two soil incubations consisting of 267 days and 135 days respectively, we collected experimental data representing the amount of carbon lost through microbial respiration throughout the incubations. We then applied first order multi-pool exponential decay models to our data to project the amount of carbon lost beyond the incubation timescales to 100 years. From these projections, we compared various steady state scenarios of applying byproduct to soil and found support for our hypothesis.