Mass spectrometry for the monitoring and control of fermentation processes
Abstract
The development of a membrane introduction mass spectrometry system with flow injection analysis is described for the monitoring of the butanediol fermentation by the organisms Bacillus polymyxa and Klebsiella oxytoca. The microbial production of 2,3-butanediol, which has value as a fuel and as a chemical feedstock, is accompanied by the production of a series of coproducts, being acetic acid, acetoin and ethanol. The products appear as a function of the degree of oxygen limitation experienced by the organism during fermentation. Under totally aerobic conditions the cells use energy efficient respiratory pathways to produce cell mass and carbon dioxide. As the biomass increases, oxygen becomes limiting if its supply is not proportionally increased and the cells turn to less energy efficient fermentative pathways to supply the energy required for growth. These fermentation pathways give rise to the coproducts. The heart of the system is a silicone membrane which selectively admits nonpolar compounds to the mass spectrometer for detection. A reaction step is necessary in order that the product acetic acid be detected because of its ionic nature in the fermentation broth. In addition to providing on-line concentration measurements of the four major products, in close agreement to more conventional off-line measurements, the mass spectrometry system provides measurements of oxygen and carbon dioxide as dissolved gases and also present in the off-gas stream. Dissolved gases are easily transported across the silicone membrane whereas the off-gases are admitted directly into the mass spectrometer. A reaction network has been developed which allows for the estimation of glucose and biomass concentrations from on-line measurements, thereby completing the knowledge of the state of the fermentation. The on-line product measurements, in particular the rate of formation of acetic acid, are used to control the concentration of oxygen in the inlet gas feed stream to the fermentation. Successful feedback control is demonstrated with the mass spectrometer system, in conjunction with a personal computer, in controlling feed gas composition and affecting the product distribution during fermentation.
Degree
Ph.D.
Advisors
Tsao, Purdue University.
Subject Area
Chemical engineering
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