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The pH‐auxostat as a tool for studying microbial dynamics in continuous fermentation
Author(s) -
Larsson G.,
Enfors S.O.,
Pham H.
Publication year - 1990
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.260360303
Subject(s) - fermentation , substrate (aquarium) , steady state (chemistry) , chemistry , inlet , yield (engineering) , alkali metal , industrial fermentation , volumetric flow rate , hydrogen , biomass (ecology) , chromatography , analytical chemistry (journal) , materials science , biochemistry , thermodynamics , organic chemistry , ecology , biology , mechanical engineering , physics , engineering , metallurgy
If a microorganism has a growth coupled production or consumption of acid or alkali, it is possible to use the pH‐auxostat as a means of control in continuous fermentation. In using the pH‐auxostat, it is possible to separate the inlet substrate flow in two different streams. These will both be pH controlled, with one main flow, consisting of nutrients and a second minor but concentrated flow, of acid or alkali. Hereby, it is possible to vary the difference in pH between the fermentor and the inlet medium. This pH difference is proportional to the steady‐state cell mass concentration. 1,2 It is shown that by separating the inlet flow in two different streams and cultivating without any substrate limitation, the maximum growth rate may be obtained while the cell mass concentration will be controlled. This will also give the possibility to reach high cell mass concentrations at μ max without the risk of wash‐out. A modified expression, based on hydrogen, of the steady‐state bio‐mass concentration, X , is developed as\documentclass{article}\pagestyle{empty}\begin{document}$$ X = Y_{X/H} \cdot [F_{{\rm Hin}} /(F_{{\rm Hin}} + F_{{\rm Min}} )] \cdot (C_{{\rm Hin}} - C_{{\rm HFERM}} ) $$\end{document} where Y X / H is the yield coefficient of cell mass per acid produced. The indexes Hin and Min refer to the inflows of alkali and medium, respectively; C Hin is the inlet concentration of hydrogen ions. The boundary condition for the cell mass shows that S in > X / Y X / S , where S in is the medium substrate concentration and Y X / S is the yield of biomass per consumed substrate. It is shown that when the cell mass concentration exceeds this value, the flow stops. The applicability of the pH‐auxostat method is then verified from different experiments. It is hereby used to detect a deviation from the maximal growth rate showing effects on the microbial physiology. With Escherichia coli used as the model organism, the effect on the growth rate of temperature and high concentration of ammonia were investigated.