Experimental Study of Biodegradation of Ethanol and Toluene Vapors

4.3.2 Batch Growth on Benzyl Alcohol
The results of batch growth with benzyl alcohol at different initial
concentrations are shown in Figures 4-9a-b. The results indicate that the higher the
initial concentration, the longer the lag phase, i.e., it takes longer time for bacteria to
adapt to the environment. For instance, the lag phase is around 3 hours at an initial
benzyl alcohol concentration of 0.7 g/L, while it took the bacteria 5 and 18 hours to
adapt to the environment at initial concentrations of 2.0 and 2.8 g/L, respectively. This
is a typical indication of substrate inhibition. Figure 4-10 gives the results of the
specific growth rates with respect to benzyl alcohol concentrations. The specific growth
rate decreases dramatically at benzyl alcohol concentrations above 1.0 g/L indicating
that benzyl alcohol inhibited the growth of Pseudomonas putida (ATCC 23973). An
empirical relationship (Luong, 1987) was used to correlate benzyl alcohol inhibition:
S
= μ
K + S
m
n
μ ( 1−
)
(4-10)
s
S
S
m
where S m is the maximum substrate concentration above which growth is completely
inhibited . Since it is known that Pseudomonas putida has a low Monod saturation
constant when growing on aromatic substrates (Hill and Robinson, 1975), K s can be set
to as low as 1 mg/L. The value of S m was found to be 2.9 ± 0.05 g/L (i.e., 0.19 C-
mol/L) by best fitting experimental results using Equation 4-10 (See Figure 4-10). This
was further proved by the experimental results, i.e., when benzyl alcohol initial
concentration is higher than 3.0 g/L, benzyl alcohol concentration remains the same
level as the initial concentration and no biomass growth was detected within 48 hours,
such as the results shown in Figure 4-9b at an initial concentration of 4.0 g/L.
61