ENGS 88 Honors Thesis (AB Students)

Degree Program


Year of Graduation


Faculty Advisor

Caitlin Hicks Pries, Lee Lynd

Document Type

Thesis (Senior Honors)

Publication Date

Spring 2021


As the production of biofuels increases to meet the demands of a growing low carbon economy, questions of sustainability surrounding its feedstock and waste streams have become increasingly relevant. In the biofuel production process, crop residues like corn stover are harvested from the field and converted to biofuels leaving generating a residue called high lignin fermentation byproduct (HLFB). From extensive process modelling in the literature, it is suggested that HLFB should be either combusted to fuel auxiliary conversion processes or returned to the soil in place of the crop residues that were harvested. Currently, there is little literature testing the actual impacts of HLFB return to the soil. This thesis serves as a first step in a larger project to provide the second ever non-modelling experimentally based results of HLFB return. In particular, this thesis serves as the base case of HLFB return comparisons ie. what happens to soil organic carbon content when corn stover is not harvested and left on the field. This thesis documents soil incubation experiments in which a Palouse soil and two sizes of corn stover are incubated over the course of 89 days and ongoing. Carbon flux and the amount of carbon respired are measured throughout the incubation period in order to ascertain how much carbon is left in the soil and how much carbon is respired by the microbial biomass in the soil. Additionally, mathematical models were applied to the data collected to set up future experiments for long term observation. Results indicated that the corn stover treatments retained approximately 93% of their soil organic carbon content, carbon respiration rate is significantly affected by moisture content, particle size is not a significant determinant of carbon respiration, and finally that a two pool parallel model fits the decomposition of the corn stover the best. Thus, experimental best practices were successfully established in this thesis and will be used and improved upon in future work on this topic.