Experimental Study of Biodegradation of Ethanol and Toluene Vapors

into the oxygen-saturated liquid and the sensor reading was recorded every 10 seconds
until the reading reached a constant value. The response time of the probe was then
determined by best fitting the oxygen concentration - time profile using non-linear, least
square regression.
The first step in conducting the measurements of oxygen transfer to the aqueous
phase in the bioreactor involved deaerating the liquid using nitrogen gas. Once the
oxygen meter indicated a stable concentration near zero, the flow of nitrogen gas was
stopped and air was introduced at a constant flow rate of 3.5 L/min (0.3 vvm). The
concentration of oxygen in the aqueous phase was recorded every 10 seconds until the
oxygen concentration was constant. The experiments were carried out at different
impeller speeds (135, 300, 450 and 600 rpm) and at different ethanol concentrations (0,
1, 3, and 8 g/L ethanol in distilled water).
C-1.1 Determination of Probe Response Time
The probe response tests were carried out at different concentrations of ethanol. The
equation used for best fitting the response time (using non-linear, least square
regression) was:
C
t
* t / t
= C (1 − e e
)
(C-1)
o2
The results of the probe response time are shown in Figure C-1. Probe response time is
related to O 2 permeability through the probe membrane. The results in Figure C-1 show
that increasing ethanol concentration increases the probe response time, and therefore
must hinder the O 2 diffusion through the membrane pores. This phenomenon was
modeled by the following empirical equation:
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