Measuring and testing – Gas content of a liquid or a solid
Patent
1994-05-26
1996-09-03
Williams, Hezron E.
Measuring and testing
Gas content of a liquid or a solid
73 6144, 73 5415, C12M 0134, G01R 1152, G01N 1100
Patent
active
055512810
DESCRIPTION:
BRIEF SUMMARY
This invention relates to determination of gas hold-up in a fermentation process and has wider implications for determination of cellular biomass or biovolume and to processes in which such determination is made.
One of the most important variables in a fermentation or other process using biological cells is the reactor biomass concentration, that is the concentration of microbial or other biological cells in the reactor, because the productivity of a process under a given set of conditions is proportional to the biomass concentration.
For monitoring purposes during a fermentation it is particularly useful to be able to estimate the biomass on a real time basis rather than at some time in the past. This generally requires the utilisation of physical properties that can be measured in situ rather than properties which require sampling and analysis. However, the conditions within fermentation reactors do not lend themselves to the use of all physical techniques.
In prior artwork done by the Applicant European Patent No. 0281602 and published European Patent Application No. 0282532 describe a method and apparatus for the determination of biomass in a culture medium in which a signal dependent on the electrical capacitance or dielectric permittivity is generated, at a suitable frequency or range of frequencies, between electrodes mutually spaced in the medium, and determining from the capacitance or permittivity dependent signal, the volume of total liquid in a net volume fraction enclosed by the cytoplasmic membranes of the cells.
The basis of this approach is that biological cells, in contrast to macromolecules, ionic solutions and gas bubbles, have molecularly thin lipid membranes which (when measured at suitable frequencies) can be shown to have a large electric capacitance per unit membrane area. When suspended in a conductive medium, the measured capacitance exhibits a frequency dependence known as the beta dispersion. By measuring the capacitance at suitable frequencies it is possible to estimate the magnitude of the beta dispersion and in turn the biomass concentration.
In a development of the above approach a conductance signal representative of the culture conductivity at respective high and low frequencies may also be used.
These methods work in many processes, but a problem that limits their accuracy is the varying quantity of gas that may be present in the culture. During fermentation the medium in a bioreactor may consist of multiple phases o gases, liquids and solids, and because the permittivity of gases is significantly lower than that of liquids, the presence of gas bubbles decreases the measured capacitance or conductance of the suspension causing errors in the biomass concentration estimate. This problem can be minimized by maintaining a constant level of aeration during the reaction and calibrating the apparatus for that level. However in some circumstances it may not be convenient or possible to keep gas hold-up constant even when aeration rate is constant and it is desirable to have a measuring technique for gas hold-up.
Accordingly the invention provides a method of determining gas hold-up in a fermentation culture, the method comprising, prior to aeration and during fermentation, inputting a high frequency alternating signal to electrodes in electrical contact with the culture, determining the magnitude of the current signal leading the voltage in the electrode circuit and using the difference in said magnitudes prior to aeration and during fermentation as a measure of the gas hold-up.
The invention also provides apparatus for determining gas hold-up in a fermentation culture, the apparatus comprising means for inputting a high frequency alternating signal to an electrode circuit that includes electrodes in electrical contact with the culture, means for inputting the voltage over the inter electrode gap to a phase sensitive detector, means for imposing a 90.degree. phase lag on a current signal from the electrode circuit and for inputting said lagged signal to the phase sensitive detec
REFERENCES:
patent: 4810650 (1989-03-01), Kell et al.
patent: 4810963 (1989-03-01), Blake-Coleman et al.
patent: 4965206 (1990-10-01), Kell
patent: 5260667 (1993-11-01), Garcia-Golding et al.
patent: 5272444 (1993-12-01), Cox
patent: 5289716 (1994-03-01), Schumacher
Wiggins J. David
Williams Hezron E.
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