Experimental Study of Biodegradation of Ethanol and Toluene Vapors

Figure 5-13a shows that the lower the initial benzyl alcohol concentration, the shorter
the lag phase. This is caused by the inhibition effect of benzyl alcohol. The results also
indicate that the closer the initial concentration is to the maximum inhibition
concentration (C b,max ), the lower the specific growth rate until it reaches zero, where the
substrate concentration stays unchanged. At the initial concentration of 2.5 g/L, the lag
phase is around 10 hours, i.e. the cells need a much longer time to overcome the high
inhibitory concentration of substrate.
Figure 5-13b shows the oxygen consumption rate (Qo), calculated from
Equation (5-59a)) and carbon dioxide formation rate (Qc), along with the ammonia
(C n ), substrate (benzyl alcohol, S) and biomass (X) concentrations at an initial
concentration of benzyl alcohol of 1.0 g/L. Similar to batch growth on ethanol, the peak
oxygen demand appears near the end of the log phase. The maximum oxygen supply is
higher than the maximum oxygen demand of 0.35 g/L-h. Thus, oxygen is not ratelimiting
substrate for this case. The results also indicate that after the benzyl alcohol
was completely consumed (S=0), there is still sufficient ammonia in the medium (C n =
0.2 g/L after S=0). Figure 5-13c shows that the ATP consumption (r_ATP) reaches a
higher value when the log phase starts. A peak in the production of μ C
x
, and thus the
ATP consumption, occurs near the end of the exponential phase and the approach to the
stationary phase.
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