Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Nakhla, George

Abstract

The aim of this study was to examine volatile fatty acid (VFA) production from a proteinaceous substrate, bovine serum albumin (BSA) for a pH range of 5 – 9, and to further assess its impact on hydrogen production in a co-fermentation process using starch and BSA at different ratios. The established optimum conditions for VFA production from BSA were an initial pH of 8, incubation time of 3 days and an operating temperature of 37 ℃. Using these fermentation conditions, the stoichiometric reactions that describe the anaerobic degradation of BSA were investigated. A methodology that describes organic acid production from BSA by using a single stoichiometric reaction was developed. With the amino acid content of BSA and by selecting the dominant amino acid fermentation reaction pathways, it was feasible to determine the stoichiometric coefficients of the dominant VFA in the single reaction step. Hydrogen production from the co-fermentation of starch and BSA in batch system was studied for five different ratios (C1 – C5). The co-fermentation process had a synergistic impact on hydrogen production and the optimum ratio occurred at C4 (80% starch + 20% BSA) with a hydrogen yield of 350 mLH2/gCODadded which was 38% higher than the expected. MINITAB-16 was used for data analysis, 3D contour diagrams and response (VFA, ammonia, and hydrogen) optimizations for C4 (80% starch + 20% BSA) were developed. The regression analysis of the responses adequately followed second-order polynomial models. The optimum concentration range for VFA and ammonia at which pH control was not necessary obtained from the Box-Behnken design were respectively 125 – 133 mg/L and 41 – 47 mg/L. Thus, the fermentative hydrogen production process would be feasible without pH control at a carbohydrate-to-protein COD ratio of 4:1.

Summary for Lay Audience

Presently, most of the global energy demand is met with fossil fuels which are rapidly depleting. In addition, fossil fuels produce greenhouse gases on combustion and contribute to climate change, global warming, and ozone layer depletion. There have been considerable efforts towards the development of biofuels that will be sustainable to meet the dual challenges of meeting future energy demands and also minimizing adverse environmental impacts. Biohydrogen can provide a solution to the aforementioned concerns as a sustainable and better replacement for fossil fuels. Microorganisms mediate the production of biohydrogen from organic feedstock and carbohydrates are the most preferred organic source. However, microbial breakdown of carbohydrates as the only feedstock produces substantial organic acids which lower the fermentation pH to a level detrimental to the activity of the microorganisms. In this study, as the anaerobic digestion of proteins produces ammonia which has the potential to counteract the abrupt pH drop as a result of the substantial organic acids production, proteins and carbohydrates were fermented at five different ratios to ascertain the optimum ratio at which pH control would not be required. The optimum ratio of 80% carbohydrates + 20% proteins was taken through statistical analyses using Response Surface Methodology and the optimization results showed that the biohydrogen production process would be feasible without pH control at a carbohydrate-to-protein ratio of 4:1.

Download

Share

COinS