On-line measurement of cell concentration using a laser turbidimeter

Abstract

The on-line measurement and control of cell concentration of Saccharomyces cerevisiae using a laser turbidimeter was carried out. Using a suspension of harvested cells, effects on the turbidity measurement of operating parameters such as agitation speed, aeration rate, and the concentration of antifoam agent were investigated with the intention of developing a more reliable measurement method than the conventional ones. Correlations between the on-line-measured turbidity and the off-line dry cell weight concentration were made at various operating conditions. In experiment, a lumped turbidity which included both cells`` and bubbles`` contributions was on-line measured and the cell concentration was estimated by using the correlations. We used an antifoam agent, Antifoam 289, and the effect of its addition to the culture broth appeared to be negligible in the concentration range tested. The aeration rate in the range of 0 to 0.5 vvm, and the agitation speed between 0 and 400 rpm had no significant influence on the sensor response. The response was, however, significantly affected by a high agitation speed of 500 rpm. The influences of these two operating parameters became negligible as the cell concentration increased. For a batch culture in which the cell concentration was lower than ca. 8 g/L, a correlation a priori constructed at the same operating conditions was used to minimize measurement errors caused by agitation and aeration. The correlation constructed in the absence of bubbles in a beaker was satisfactorily used for the on-line measurement of the cell concentration when it was higher than ca. 8 g/L. During the stationary phase of the cells after the depletion of glucose in batch cultures, considerable deviations were observed between the on-line estimate and the actual cell concentration. It is considered that those deviations were due to morphological changes of the yeast cells. The cell concentration could be satisfactorily estimated on-line in the ...