Application of multistage continuous culture to VHG based ethanol fermentations : performance and control of bacteria by PH and pulsed addition of antibiotic
Date
2002
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ORCID
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Degree Level
Doctoral
Abstract
The application of very high gravity (VHG) technology to multistage continuous
culture technology proved to be possible. Multistage fermentations were conducted with
concentrations of glucose from 152 to 312 g/L in the medium. Steady state
concentrations of Saccharomyces cerevisiae, glucose, and ethanol were established in
each fermentor at each condition tested. A maximum ethanol concentration of 17% v/v
was achieved in the last fermentor in the multistage system when 312 g/L glucose was
fermented at a dilution rate of 0.05 h-1 at 28°C. The productivity of ethanol in the
multistage system proved to be higher (12.7 g/L/h) than in identical fermentations
conducted in batch (2.4 g/L/h) or in a single stage fermentor (1.25 g/L/h). Lactobacillus
paracasei was introduced into a multistage fermentation that had been previously
brought to steady state with S. cerevisiae. The effects of the contamination were then
documented and the fermentation data were compared to the non-contaminated control.
Control of L. paracasei in the multistage continuous culture fermentation (MCCF)
system was then investigated by both pH and pulsed additions of penicillin G. Both pH
and penicillin G addition were effective at reducing (but not eliminating) L. paracasei.
The application of penicillin G every six hours (pulsed addition) to give an overall
concentration of 2475 U/L in the multistage system was 3.5 times more effective in
reducing the viable numbers of L. paracasei than penicillin G maintained continuously at
2475 U/L. Other frequencies of addition and overall average concentrations of penicillin
G were tested and documented. Lastly, various unstructured mathematical models were
run and assessed for their ability to accurately predict experimental steady state
concentrations of biomass (yeast), substrate (glucose), and product (ethanol)
concentrations in each fermentor at each condition in the multistage system. The Aiba
model (which showed the best fit to experimental data) was then used to predict the
course of the fermentation under multistage conditions.
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Degree
Doctor of Philosophy (Ph.D.)
Department
Applied Microbiology and Food Science
Program
Applied Microbiology and Food Science