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(a) (b)
Figure 4.6 Bacteria Cells in the Mixed Bacteria Sludge: a) Gram Negative and b) Gram
Positive (x1500)
4.2.2 Kinetics of Yeast and Bacterial Growth
Optimum environmental conditions are important for the growth of the
microorganisms as well as the degradation of the organic components. To assess the
optimum conditions in the systems, it is necessary to monitor the growth of the
microorganisms. This could be achieved in several ways. Respiration (oxygen
consumption) is probably the most widely tested and accepted bacterial monitoring
technique (Cairns and Van Der Schalie, 1980). Normally, bacterial respiration results in a
certain decrease in oxygen concentration in the medium depending upon the retention time
of the chamber and temperature. This oxygen uptake by the organism can help us describe
the growth pattern of the microorganism. Reeves (1976) used the respirometer to record
the oxygen uptake in the activated sludge unit.
The Oxygen Uptake Rate (OUR) refers to the rate of oxygen consumption by
aerobic bacteria per unit time (Chen, et al., 1997). It is produced by the slope of the
relationship between the dissolved oxygen and the exposure time. By measuring the
oxygen uptake rate, one can indirectly obtain the specific growth rate of the
microorganisms as rate of the oxygen uptake is stoichiometrically related to the organic
utilization rate and the growth rate. The operation condition used in the biokinetic studies
in the bacterial and yeast reactor is described in Table 3.3. In the treatment process, the
substrate concentration and the limiting nutrients has an effect on the specific growth rate
of the microorganism. The effect of the substrate concentration in the bacterial and yeast
culture is given the Figure 4.7 and 4.8, respectively.
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