Measurement of dissolved carbon dioxide' J. S . ALFORD,JR.
Can. J. Microbiol. Downloaded from www.nrcresearchpress.com by University of P.E.I. on 11/23/14 For personal use only.
Atrtihiotic Mnnr!firctriring rrtlrl Dei~eloptrretltDii.i.sion, Eli Lilly cltlrl Comprrtly, Indicrtlapolis, It1diatla 46206 Accepted August 29, 1975 ALFORD,J . S.. JR. 1976. Measurement of dissolved carbon dioxide. Can. J. Microbiol. 22: 52-56. Several probes for measuring dissolved carbon dioxide (CO,) concentration were installed in a 68-litre fermentor and their effectiveness compared. Submerged silastic rubber tubing gave reproducible results over a wide range of operating conditions and was generally superior to all other probes evaluated. The silastic rubber probe was used to compare the partial pressure of CO, in viscous fermentation media with that in the fermentor exhaust gas. No significant difference was found. Results show that determination of the CO, partial pressure in the exhaust g a s gives an excellent approximation of the partial pressure of dissolved C 0 2 in the liquid medium, eliminating the need for measurement of C 0 2 concentration in the broth. ALFORD.J . S.. J R . 1976. Measurement of dissolved carbon dioxide. Can. J . Microbiol. 22: 52-56. Plusieurs klectrodes pour mesurer les concentrations de dioxide de carbone dissous furent installkes dans un fermentateur d e 68 litres et leurs efficacitks furent comparees. L e s tubes en caoutchouc silastic submerges donnent les r e s ~ ~ l t ales t s plus reproductiblesau coursd'une grande varikte de conditions d'operations et sont generalement superieurs a toutes autres electrodes evaluees. L'klectrode en caoutchouc silastic fut utilisee pour comparer les pressions partielles d e CO2 dans des milieux de fermentation visceux avec cellesde I'kchappement de gazdesfermentateurs. Aucune difference significative n'a kt&trouvke. Les res~lltatsmontrent que la dktermination de la pression partielle du C 0 2 dans les gaz d'kchappement donne une excellente approximation d e la pression partielle du CO, dissous dans le milieu liquide, kliminant ainsi le besoin de mesurer la concentration du C 0 2 dans le bouillon. [Tr~tduitpar le journal]
Introduction Current studies in fermentation indicate a n increased interest in the measurement of dissolved gas concentration, oxygen uptake, and carbon dioxide evolution. Measurenient of these parameters requires the use of dissolved gas probes and of suitable analytical equipment to determine gas concentrations in the fermentor exhaust. The purpose of this study was to test the hypothesis that the partial pressure of dissolved carbon dioxide in the fermentation media was about the same as the partial pressure in the exhaust gas. If this is true, the need for a dissolved C0,-measuring probe would be eliminated. Theoretical CO, is produced by cells during the process of respiration. Some CO, exists in a dissolved state and some dissociates into bicarbonate ion. The IReceived May 30, 1975.
dissolved CO, equilibrates with the bicarbonate ion, a process which occurs almost instantaneously (4). Mass transfer tends to occur whenever a CO, partial pressure gradient exists, such a s from medium next to respiring cells to bulk medium and then to the sparging air stream a t appreciable distances from respiring cells. The processes involved in CO, transport can be considered as overcoming three resistances in series. Tliese resistances are briefly described below, with particular emphasis placed on the effect of viscosity. Viscosity represents the most significant difference between media used in previous published studies a n d most commercial fermentation media. Dissolved CO, nearest respiring cells must first diffuse through the medium until it comes in contact with the interface of a sparging gas bubble. This diffusion is characterized by a 'diffusivity' which, for many systems, has been found to be inversely proportional to medium viscosity.
-
ALFORD JR.: MEASUREMENT OF DISSOLVED CO, Exhaust
Partial Pressure of co,
Can. J. Microbiol. Downloaded from www.nrcresearchpress.com by University of P.E.I. on 11/23/14 For personal use only.
Bulk liquid Cells
, l l i q u i d Gas Film Film
I I
1 Bulk
1 Gas
FIG. 1. Partial pressure profile for two-film model.
N,
Once dissolved C 0 , conies in contact with the interface of a gas bubble where a CO, partial pressure gradient exists, the second and third phases of CO, transport take place. These phases are characterized by an interface between a gas and liquid film as shown in Fig. 1. It is generally accepted that the overall mass transfer coefficient, KLa ( K L a z k L a ) , is controlling for the absorption and desorption of a sparingly soluble gas such as CO,. Therefore, CO, transport across the liquid gas interface, at steady state, can be described by eq. 2: [2] Nco, transferred = KLa (CO, P.P.* in equilibrium with gas - P.P. CO, in bulk liquid) where the partial pressure difference is the driving force, and KLa represents resistance to mass transport. The KLa term is a function of many parameters including viscosity. For example, Ryu and Humphrey (7) showed that, for a penicillin culture with an apparent viscosity of 50-300 pseudo-centipoise (cp), lcLa was related to apparent viscosity (q) as follows: Thus, increasing viscosity will result in decreasing /
Can. J. Microbiol. Downloaded from www.nrcresearchpress.com by University of P.E.I. on 11/23/14 For personal use only.
Atrtihiotic Mnnr!firctriring rrtlrl Dei~eloptrretltDii.i.sion, Eli Lilly cltlrl Comprrtly, Indicrtlapolis, It1diatla 46206 Accepted August 29, 1975 ALFORD,J . S.. JR. 1976. Measurement of dissolved carbon dioxide. Can. J. Microbiol. 22: 52-56. Several probes for measuring dissolved carbon dioxide (CO,) concentration were installed in a 68-litre fermentor and their effectiveness compared. Submerged silastic rubber tubing gave reproducible results over a wide range of operating conditions and was generally superior to all other probes evaluated. The silastic rubber probe was used to compare the partial pressure of CO, in viscous fermentation media with that in the fermentor exhaust gas. No significant difference was found. Results show that determination of the CO, partial pressure in the exhaust g a s gives an excellent approximation of the partial pressure of dissolved C 0 2 in the liquid medium, eliminating the need for measurement of C 0 2 concentration in the broth. ALFORD.J . S.. J R . 1976. Measurement of dissolved carbon dioxide. Can. J . Microbiol. 22: 52-56. Plusieurs klectrodes pour mesurer les concentrations de dioxide de carbone dissous furent installkes dans un fermentateur d e 68 litres et leurs efficacitks furent comparees. L e s tubes en caoutchouc silastic submerges donnent les r e s ~ ~ l t ales t s plus reproductiblesau coursd'une grande varikte de conditions d'operations et sont generalement superieurs a toutes autres electrodes evaluees. L'klectrode en caoutchouc silastic fut utilisee pour comparer les pressions partielles d e CO2 dans des milieux de fermentation visceux avec cellesde I'kchappement de gazdesfermentateurs. Aucune difference significative n'a kt&trouvke. Les res~lltatsmontrent que la dktermination de la pression partielle du C 0 2 dans les gaz d'kchappement donne une excellente approximation d e la pression partielle du CO, dissous dans le milieu liquide, kliminant ainsi le besoin de mesurer la concentration du C 0 2 dans le bouillon. [Tr~tduitpar le journal]
Introduction Current studies in fermentation indicate a n increased interest in the measurement of dissolved gas concentration, oxygen uptake, and carbon dioxide evolution. Measurenient of these parameters requires the use of dissolved gas probes and of suitable analytical equipment to determine gas concentrations in the fermentor exhaust. The purpose of this study was to test the hypothesis that the partial pressure of dissolved carbon dioxide in the fermentation media was about the same as the partial pressure in the exhaust gas. If this is true, the need for a dissolved C0,-measuring probe would be eliminated. Theoretical CO, is produced by cells during the process of respiration. Some CO, exists in a dissolved state and some dissociates into bicarbonate ion. The IReceived May 30, 1975.
dissolved CO, equilibrates with the bicarbonate ion, a process which occurs almost instantaneously (4). Mass transfer tends to occur whenever a CO, partial pressure gradient exists, such a s from medium next to respiring cells to bulk medium and then to the sparging air stream a t appreciable distances from respiring cells. The processes involved in CO, transport can be considered as overcoming three resistances in series. Tliese resistances are briefly described below, with particular emphasis placed on the effect of viscosity. Viscosity represents the most significant difference between media used in previous published studies a n d most commercial fermentation media. Dissolved CO, nearest respiring cells must first diffuse through the medium until it comes in contact with the interface of a sparging gas bubble. This diffusion is characterized by a 'diffusivity' which, for many systems, has been found to be inversely proportional to medium viscosity.
-
ALFORD JR.: MEASUREMENT OF DISSOLVED CO, Exhaust
Partial Pressure of co,
Can. J. Microbiol. Downloaded from www.nrcresearchpress.com by University of P.E.I. on 11/23/14 For personal use only.
Bulk liquid Cells
, l l i q u i d Gas Film Film
I I
1 Bulk
1 Gas
FIG. 1. Partial pressure profile for two-film model.
N,
Once dissolved C 0 , conies in contact with the interface of a gas bubble where a CO, partial pressure gradient exists, the second and third phases of CO, transport take place. These phases are characterized by an interface between a gas and liquid film as shown in Fig. 1. It is generally accepted that the overall mass transfer coefficient, KLa ( K L a z k L a ) , is controlling for the absorption and desorption of a sparingly soluble gas such as CO,. Therefore, CO, transport across the liquid gas interface, at steady state, can be described by eq. 2: [2] Nco, transferred = KLa (CO, P.P.* in equilibrium with gas - P.P. CO, in bulk liquid) where the partial pressure difference is the driving force, and KLa represents resistance to mass transport. The KLa term is a function of many parameters including viscosity. For example, Ryu and Humphrey (7) showed that, for a penicillin culture with an apparent viscosity of 50-300 pseudo-centipoise (cp), lcLa was related to apparent viscosity (q) as follows: Thus, increasing viscosity will result in decreasing /
