Direct monitoring of reactor biomass in fermentation control

Lactic Acid Bacteria Biomass Monitoring in Highly Conductive Media by Permittivity Measurements

Recent technological improvements have extended the application range of permittivity biomass measurements to bacterial fermentations in highly conductive media. With Lactobacillus casei, the effective biomass detection sensitivity of the FOGALE Biomass System is around 0.2 g/l (0.01 pF/cm). Fermentations growth kinetics of Lactobacillus casei can be recorded with good reproducibility and accuracy despite the high medium conductivity varying between 15 and 75 mS/cm, and the low cell concentration (<6 g/l).

Biomass determination

The reasons for and historical backgrounds of biomass determination are discussed under the aspects of theoretical and practical importance, usefulness and representativity. Off-line methods are evaluated and compared with on-line methods; constraints of applications and conclusiveness of results are rated. Special emphasis is given to the fact that mere knowledge of a bio-mass concentration is not sufficiently valuable to learn more about physiology nor to determine the effectiveness of a biotechnological process. A combination of several different alternative measuring principles in parallel as well as the exploitation of software sensors is proposed as a promising future solution.

Apparatus for the electrical characterisation of conductive fluids

Non-invasive and fully automated conductimetric measurements of electrolyte and bacterial samples were achieved in a closed volume test cell, comprising a magnetic field coil and detector. By monitoring field induced currents in sample electrolytes the magnitude of the sample current was shown to vary as the inverse of the sample impedance. The impedance characteristic was shown to be that of an LCR resonant circuit. This characteristic is primarily a function of the applied frequency and the solution/cell properties being dependent on the solution conductivity and dielectric permittivity at any given concentration. Small changes in sample dielectric permittivity in the presence of a large background conductivity are shown to be significant. The apparatus described can provide fixed or swept frequency conductivity measurements in the range 1 kHz to 2.25 MHz with a lower conductivity sensitivity of 0.9 x 10(-3) Scm-1. Bulk impedimetric characteristics of cell suspensions are derived by a two stage measurement.