Experimental Study of Biodegradation of Ethanol and Toluene Vapors

2.3.2 Growth Models with Inhibition
At high concentrations of all substrates, growth becomes inhibited and growth
rate depends on inhibitor concentrations. The inhibition pattern of microbial growth is
analogous to enzyme inhibition. If a single enzyme-catalyzed reaction is the ratelimiting
step in microbial growth, then kinetic constants are biologically meaningful.
Often, the underlying mechanism is complicated and kinetic constants of unstructured
growth models do not then have biological meanings. The effects of increasing the
inhibitor concentrations are similar to the effects of enzyme reaction inhibitors. Thus,
the expressions for enzyme inhibition can be applied to model cell growth inhibition.
Some enzyme inhibition models are shown below (Shuler and Kargi, 2002):
Non-competitive substrate inhibition (Haldane inhibition model):
μ
max
μ =
(2-3)
K
s S
(1 + )(1 + )
S K
if K i >> K s , then
i
μ
maxS
μ =
(2-4)
2
S
(1 + S + )
K i
Competitive substrate inhibition:
μ max
S
μ =
(2-5)
S
K
s
(1 + ) + S
K
i
where K i is the inhibition constant.
Luong (1987) proposed an empirical relationship to correlate substrate inhibition:
S
= μ
K + S
m
n
μ ( 1−
)
(2-6)
s
S
S
m
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