The relationship between the cellulolytic Clostridium termitidis and the electrogenic Geobacter sulfurreducens was evaluated in terms of co-culture sustainability and hydrogen production. Batch co-culture experiments in triplicate balch tubes were conducted using cellobiose as the sole carbon source and fumarate as a terminal electron acceptor. Despite high initial concentrations of acetate, no formate and very low H2 concentrations were detected, supporting the hypothesis that a syntrophic association exists between both bacteria. Co-culture growth characterization experiments were repeated in three microbial electrolysis cells and cellobiose as the sole carbon source. Initially, 9.7 mol-H2 mol-1-glucose was produced. However, a sustainable co-culture could not be maintained despite efforts to reduce reactor temperature and triple the medium’s buffering capacity. Strategies to achieve a sustainable co-culture are to minimize the carbon flux through C. termitidis by using complex substrates, maintain neutral operating conditions, and introduce acetogenic bacteria to control the flux of metabolic intermediates.

Ethanol production through biomass fermentation is one of the major technologies available to produce liquid fuel from renewable energy sources. A major problem associated with the production of ethanol through fermentation remains the inhibition of the yeast Saccharomyces cerevisiae by the produced ethanol. Currently high water dilution rates are used to keep the ethanol concentrations in the fermentation broth at low concentrations, resulting in low yields and increased downstream processing to remove the excess water. Yeast strains that have a high tolerance for ethanol have been isolated but the time and cost associated with doing so poses a challenge. The fermentation process can be combined with pervaporation, thereby continuously removing ethanol while it is being formed. In this study a mathematical model for ethanol fermentation with yeast, Saccharomyces cerevisiae, coupled with pervaporation was developed. The fermentation of glucose was optimised in the first part of the study and experimental data were obtained to find a kinetic model for fermentation. It was found that an optimum ethanol yield can be obtained with an initial glucose concentration of 15wt%, a yeast concentration of 10 g.L–1, and a pH between 3.5 and 6. The maximum ethanol yield obtained in this study was 0.441g.g–1 (86% of the theoretical maximum) using 15wt% glucose, 10g/L yeast and a pH of 3.5. Two kinetic models for fermentation were developed based on the Monod model. The substrate–limiting model, predicted fermentation very accurately when the initial glucose concentration was below 20wt%. The second model, the substrate–inhibition model, predicted fermentation very well when high initial glucose concentrations were used but at low glucose concentrations, the substrate–limiting model was more accurate. The parameters for both models were determined by non–linear regression using the simplex optimisation method combined with the Runge–Kutta method. The PERVAP®4060 membrane was identified as a suitable membrane in this study. The effect of the ethanol content in the feed as well as the influence of the glucose content was investigated. The total pervaporation flux varied with ethanol content of the feed and the highest total flux of 0.853 kg/m2h was obtained at a feed with 20wt% ethanol. The addition of glucose had almost no effect on the ethanol flux but it lowered the water flux, thereby increasing the enrichment factor of the membrane. The mass transport through the PERVAP®4060 membrane was modelled using the solution–diffusion model and Greenlaw’s model for diffusion coefficients was used. The limiting diffusion coefficient (Di0) and plasticisation coefficients (Bij) were determined by using the Nelder–Mead simplex optimisation method. The theoretical values predicted with the model showed good agreement with the measured experimental values with R2 values above 0.998. In the third part of this investigation, the kinetic model developed for fermentation was combined with the transport model developed for pervaporation. The combined kinetic model was compared to experimental data and it was found that it could accurately predict fermentation when coupled with pervaporation. This model can be used to describe and better understand the process when fermentation is coupled with pervaporation. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

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Chopped alfalfa and chopped whole-plant corn were ensiled and the proteolytic changes which occurred during ensiling were investigated. Proteolysis was measured in terms of end-products of protein degradation and by protein isolation followed by electrophoresis. The effects of formic acid and ammonia, applied at the time of ensiling, on proteolytic changes were investigated. / Alfalfa treated with formic acid contained significantly reduced levels of NH$ sb3$-N and NPN compared to control silage; ammonia (NH$ sb3$)-treated alfalfa silage had significantly less NPN (P $<$ 0.05). After 90d of storage, formic acid-treated and NH$ sb3$-treated alfalfa silage contained lower levels of both branched and non-branched amino acids, sulfur containing, and basic amino acids compared to control silage; formic acid-treated and NH$ sb3$-treated corn silage contained lower levels of branched chain amino acids and sulfur containing amino acids after the same time period. Formic acid and ammonia were most effective in the reduction of proteolysis in alfalfa silage and corn silage, respectively. The protein ribulose 1,5-diphosphate carboxylase (RuDPCase) was depleted completely after 2d of fermentation in control silage. Conditions in NH$ sb3$-treated alfalfa silage stabilized RuDPCase during the first 24h of storage.

The potential of surfactants for improving the yields of alpha-amylase during the solid substrate fermentation (SSF) of potato starch using pure and mixed cultures was examined. The microorganisms used in this study were Aspergillus oryzae ATCC 1011, Bacillus subtilis ATCC 21556 and Bacillus subtilis ATCC 21332. The surfactants tested were Tween 20, Tween 80, SDS and surfactin. The fermentations were carried out in perforated trays after the addition of 10% (v/w) inoculum and with temperature and humidity controlled at 30°C and 90% RH respectively. Samples were taken and analyzed quantitatively for the production of alpha-amylase and biomass and qualitatively by scanning electron microscopy (SEM) using a JSM-840 A scanning microscope at 10 kV accelerating voltage. / It was possible to increase fungal alpha-amylase production by as much as 6 fold in the process with the addition of either synthetic surfactants or the biosurfactant surfactin. The bacterial alpha-amylase yields increased up to 11.5 fold in with the addition and/or the co-culture production of surfactants. The highest enzyme activity was found in the fermentation of a mixed culture of the two Bacillus strains with the addition of Tween 80. During the SSF with B. subtilis ATCC 21332 and ATCC 21556 as a mixed bacterial culture, there was also the production of surfactin in yields comparable to those obtained in a submerged fermentation. The biofilm formation as observed by SEM appeared to be associated with the presence of surfactants in the process and was not formed when no surfactants were present. The biofilm was observed as an entrapment of the bacteria in the substrate, resulting in improved access to the starch and higher production of alpha-amylase.

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Errata slip inserted on back end-paper. / Bibliography: leaves 106-125. / vii, 125 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 1999

Zugl.: Hohenheim, Univ., Diss., 2007