Extractive fermentation in a continuous bioreactor to produce lactic acid
Abstract
The main objective of this research is to develop a fermentation/separation process to produce pure lactic acid at a lower cost. Batch and continuous fermentation kinetics of Lactobacillus bulgaricus were examined in detail. A maximum productivity of 6.2 g/L. hr was obtained at pH 5.6 for the CSTR system, which was three times the productivity obtained for a batch system at the same pH. Solvents isoamyl alcohol and aliquat were used in a hollow fiber extractor to extract lactic acid. About 54% and 94% of lactic acid was extracted from the aqueous phase at a solvent/aqueous flow rate of 8.0 by isoamyl alcohol and aliquat, respectively. Lactobacillus bulgaricus was found to be compatible with the solvent isoamyl alcohol, whereas aliquat was very toxic. A CSTR with cell recycle and lactic acid extraction microporous hollow fibers was developed to produce lactic acid utilizing lactose as substrate. The reactor and extractor were modelled and analyzed separately. At a dilution rate of 2 and with 60 g/L of cellmass in the CSTR, substrate was completely utilized. Solvents isoamyl alcohol and aliquat were used in the hollow fiber extractor to extract lactic acid. At a dilution rate of 1.5, the productivity of 68 g/L.hr was achieved in the organic phase, when isoamyl alcohol was used and the CSTR and the extractor were operated at pH 5.6 and 4.0, respectively. An Immobilized Cell Reactor (ICR) was operated to produce lactic acid by utilizing lactose. Lactobacillus bulgaricus was immobilized on a cotton towel matrix. Microporous-hollow fiber membranes were used to recover lactic acid in situ to control the pH in an Immobilized Cell Reactor/Separator (ICRS). Outlet lactose concentration dropped drastically at a solvent/substrate flow ratio of 5 and a substrate flow rate of 10 mL/hr, when the ICRS was operated in two stages. The maximum organic phase lactic acid productivity was obtained in the ICRS with two stages. About 90% of the initial lactose concentration was utilized in this case and 80% of the total lactic acid productivity was in the solvent phase. Preliminary economics indicate that the ICRS process decreases the production and capital cost as compared to the conventional batch process. (Abstract shortened by UMI.)
Degree
Ph.D.
Advisors
Wankat, Purdue University.
Subject Area
Chemical engineering
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