Evaluation of Nitrifying Bacteria Specific Growth Rate Sensitivity to Carbon Dioxide for Full-Scale Activated Sludge and Municipal Wastewater

In order to control wastewater processes, on-line measurements of important process variables are crucial. This contribution focuses on the applicability of the Biomass Monitor for on-line viable biomass measurement of activated sludge from a municipal wastewater plant. In addition, the specific growth rate of the sludge is estimated on-line, based on the information derived from the device under study. Compared to dry weight measurements, the Biomass Monitor hardware offers the advantage of a biologically more appropriate observation of the biomass by only taking into account the viable cells in the population. The optimal measurement frequency of the biomass monitoring device for the given experimental conditions has been determined. Furthermore, the capacitance readings have been correlated with off-line analyses of dry weight of the sludge during the experimental phase in which no death of cells occurred. Finally, an evaluation of the estimator of the specific growth rate including its tuning is presented.

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Influence of the specific growth rate on formation of sterols in yeast Saccharomyces cerevisiae during fed-batch cultivation

Czech Journal of Food Sciences ◽

10.17221/8321-cjfs ◽

2000 ◽

Vol 18 (No. 3) ◽

pp. 110-114

Author(s):

J. Čermák ◽

M. Rychtera ◽

P. Nechvíle ◽

J. Náhlík ◽

K. Melzoch ◽

...

Keyword(s):

Carbon Dioxide ◽

Growth Rate ◽

Specific Growth Rate ◽

Control Strategy ◽

Respiratory Quotient ◽

Specific Growth ◽

Carbon Dioxide Concentration ◽

Sterol Fraction ◽

Yeast Cells ◽

Dry Biomass

Ergosterol is a major sterol in yeast cells. Intermediates of ergosterol biosynthesis or products of ergosterol biotransformation occur in cells too. Sterols mainly form components of cell membranes. Fluidity of membranes is affected by sterols. The amount of sterols in cells can be influenced above all by cultivation conditions and by the yeast genotype. Specific growth rate is an important factor which affects the amount of sterols present in yeast cells. We carried out a series of 24-hour cultivations to find out the impact of specific growth rate on sterol biosynthesis. Inflow of synthetic medium to the bioreactor was controlled by means of a profile of carbon dioxide concentration in the outlet gases. This profile was acquired by simulation according to a mathematical model of cultivation. Profile of carbon dioxide concentration corresponded to a precalculated profile of specific growth rate. Cultivation was divided into two phases with different growth rate values. A constant value of the specific growth rate was maintained in the 1st phase. The specific growth rate value decreased by controlling the inflow in the 2nd phase (beginning at 12th hour of cultivation). Other cultivations were carried out using so-called physiological control which consisted in determining the immediate physiological state (e.g., RQ) and the choice of control strategy according to the metabolic state. Selected control strategy ensures an immediate action (inflow of the medium). If the specific growth rate decreased in the 1st phase, the amount of total sterols in yeast dry biomass increased (to 2.7% in yeast dry biomass). But the purity of ergosterol decreased (amount of sterol contaminants increased up to 23.3% in the sterol fraction). If a constant value of respiratory quotient was maintained (at about 1.1), the amount of total sterols in yeast dry biomass and the purity of ergosterol were constant. If the value of respiratory quotient was changed in the growth and final phase of cultivation, the amount of total sterols in yeast dry biomass increased (to 2.83% in yeast dry biomass). However, the purity of ergosterol decreased (amount of sterol contaminants increased up to 21.2% in sterol fraction).

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