Date of Award

2008

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

Jerald Lalman

Second Advisor

Nihar Biswas

Keywords

Applied sciences, Anaerobic microbial communities, Electron fluxes, Long-chain fatty acids

Rights

info:eu-repo/semantics/openAccess

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Abstract

Long chain fatty acids (LCFAs) possessing 18 carbons were used to inhibit methanogenesis, a terminal metabolic step in the anaerobic degradation of glucose. The LCFA inhibitors diverted the electron flux towards hydrogen production in the absence of sulfate, and in the presence of sulfate (SO4 -2) the electron flux was diverted towards SO42- reduction.

The experiments were performed in batch (160 ml) reactors containing a mixed anaerobic culture which was acclimated to glucose or glucose plus sulfate at 37°C. In the case of SO4-2 reduction, the chemical oxygen demand (COD)/SO4-2 ratio was 1.25 and the LCFAs used were linoleic acid (LA; C18:2), oleic acid (OA; C18:1), and stearic acid (SA; C18:0). Diversion of electron fluxes to sulfate reducing bacteria (SRBs) was observed in cultures fed LA (> 30 % electron flow as compared to the glucose plus SO4-2 controls) and OA (> 20 % electron flow as compared to the glucose plus SO4-2 controls) plus glucose, while SA had no significant effect on sulfate removal. Sulfate reduction increased with LCFA concentration and a maximum of approximately 90 % and 70 % sulfate removal was achieved in cultures receiving LA and OA, respectively, plus glucose.

Prior to performing the hydrogen production studies, experiments were conducted to assess the synergistic effect of low pH (pH 5 or 6) and OA or LA (individual and mixtures) on hydrogenotrophic methanogens. Data from the latter work provided optimum conditions for conducting the hydrogen production studies (pH 5 and 2000 mg 1-1 LCFA). In the hydrogen production studies, hydrogen was produced and accumulated in all the LA or OA incubated cultures (ranging from 0 - 25 days in 5 days consecutive increments). In the LA or OA incubated cultures, the maximum hydrogen yield was 2.80 ± 0.20 and 2.44 ± 0.12 mole H2 mole-1 glucose, respectively. In the LCFA incubated cultures, the hydrogen yield was a function of the predominant LCFA β-oxidation byproduct prevalent during the time of analysis. All three β-oxidation byproducts, plamitic, myristic and lauric acid inhibited hydrogen consumption; however, the greatest inhibition was detected in cultures containing lauric acid.

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