Experimental Study of Biodegradation of Ethanol and Toluene Vapors

4.3 Batch Growth on Ethanol and Benzyl Alcohol
4.3.1 Batch Growth on Ethanol
One of the ethanol batch growth experiments is shown in Figure 4-7 (S 0 = 2.3
g/L). Growth started after a 5 h lag phase and was reflected exactly by ethanol
consumption in the bioreactor. The initial concentration of 2.3 g/L of ethanol was
completely consumed in less than 12 hours. At low initial ethanol concentrations no
byproduct was detected in the media and the Monod model was used to describe the
growth kinetics:
1 dX μ S
μ = = max
X dt K +
(4-9)
s
S
μ max is the maximum specific growth rate and K s is the Monod saturation constant. The
specific growth rate on ethanol during the log phase was determined by plotting ln(X)
versus time. The dissolved oxygen values were found to be higher than the critical
value (0.35 mg/L, Shuler and Kargi, 2002) for growth on ethanol at initial
concentrations up to 5.8 g/L, which indicated that oxygen mass transfer is not a ratelimiting
step under these conditions. For the batch growth experiments at ethanol initial
concentrations up to 5.8 g/L, the specific growth rates were within the range of
0.37 ± 0.03h
-1 . This rate of growth on ethanol is much greater than the maximum
specific growth rate (0.046 h -1 ) of Acetobacter aceti on ethanol reported earlier by Wei
et al., 1999. Pseudomonas putida (ATCC 23973) will therefore be much more effective
in removing ethanol from contaminated air compared to that earlier work. The growth
process is reproducible, and Figure 4-8 shows the results for two different batch runs.
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