Date of Award

2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

Lalman, Jerald A.

Keywords

Applied sciences, Chemical stressor, Homoacetogens, Hydrogenotrophic methanogens, Hydrogen production, Lignocellulosic biomass, Linoleic acid

Rights

CC BY-NC-ND 4.0

Abstract

The effects of chemical stressing agents on H 2 metabolism were evaluated using thermodynamic, biochemical, genomic and statistical methods. The objectives of this study were to examine the role of homoacetogens and hydrogenotrophic methanogens exposed to different stress treatments under various fermentation conditions. Negligible H 2 consumption was observed at mesophilic and thermophilic temperature (at pH 4.5) when combined with the addition of 2 g L -1 linoleic acid (LA). Genomic analysis revealed that LA-treated cultures were dominated by Clostridium sp. whereas control cultures were dominated by homoacetogens and methanogens. Lauric acid (LUA), LA, fish oil and furfural affected H 2 consumption similarly to BES. The H 2 consumption (%) of the control and chemically treated cultures revealed the following trend: Control > Fish oil = LA = Furfural > BES > LUA. Treatment with different stressing agents also resulted in the formation of diverse fermentation metabolites. The long-term effects of different culture pretreatments under mesophilic condition resulted in higher mean H 2 yields compared to the yields from cultures incubated at thermophilic condition (after 5 glucose additions). Hydrogen consumption studies using long term stress treated cultures showed lower consumption at thermophilic temperature than at mesophilic temperature. Uptake hydrogenase activities correlated positively with the H 2 consumption data. Genomic analysis indicated that both methanogens and homoacetogens were present in control cultures, but they were absent from the pretreated cultures. Studies conducted in anaerobic sequencing batch reactors revealed that lowering the HRT from 37.5 h to 7.5 h reduced the methane yield and increased the H 2 yield. Higher H 2 yields were obtained in cultures operated at thermophilic temperature compared to mesophilic and psychrophilic temperature using corn stalk (CS) as substrate. Cultures fed CS liquor showed lower levels of specific methanogenic activities than cultures fed pure sugars. The results from these studies indicate that all the chemical stressing agents investigated were active against H 2 consumers (methanogens in particular). In addition to different stress treatments, proper control of operational parameters such as pH, HRT and temperature is required to minimize H 2 consumption and maximize H 2 production in dark fermentation process.

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