Date of Award


Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering (PhD)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

Rebecca G. Ong

Committee Member 1

David Shonnard

Committee Member 2

Paul Doskey

Committee Member 3

Rupali Datta


Recent research reports newer sustainable technologies for bioenergy generation that would serve as an alternative to conventional petroleum sources. There is abundant research reported on individual subsets of the study that has linked growth parameters to biomass yield, treatment conditions to bioethanol production or pretreatment conditions to microbial inhibitors. However, there is a lack of literature that undertakes the entire field-to-fuel process conditions in a single study. In this thesis, we focus on isolating and characterizing secondary metabolites provoked by drought in switchgrass, an upcoming bioenergy crop, during the mid-western drought of 2012. To characterize these inhibitors, switchgrass was separately solvent extracted before and after the pretreatment method followed by sequential hydrolysis and fermentation using yeast. Our analysis concluded that adding a water extraction step prior to AFEX-pretreatment overcame the inhibition, and saponins, a class of plant-generated triterpene glycosides, potentially ceased yeast growth in the drought-stressed switchgrass. Using non-targeted mass spectrometry (negative ESI/MS and positive ESI LC-MS), we identified many known and unknown compounds in relatively higher amounts in the drought-stressed switchgrass compared to control. A molecular networking mathematical calculation was performed using an R-based software, MFAssignR, for the detected compounds (abundance, m/z and retention time) to get a better insight on empirical formula, oxidation state and aromatic index.

Further, we studied the effect of drought-like water-stress on switchgrass, simulated using rainout shelters, harvested on five “marginal lands” located across latitudinal gradient throughout Michigan and Wisconsin. In 2018, the 60% roof occlusion failed to induce water-stress on switchgrass under the shelters compared to ambient samples at the all sites except for the Hancock site. The water-stress imposed by the rainout shelters compounded with relatively low soil moisture holding capacity and high soil temperature due to sandy nature of the soil at the Hancock site resulted in reduced fermentability of switchgrass than ambient samples. However, there was no significant reduction in the biomass yield between the paired rainout and ambient samples. Hence, in the subsequent years the shelters were modified to 100% roof occlusion resulting in reduction of the biomass yield for the rainout samples compared to ambient samples.

Available for download on Wednesday, July 24, 2024