Experimental Study of Biodegradation of Ethanol and Toluene Vapors

corresponds with the value associated with 100% of the ethanol from gas stream being
dissolved in the liquid phase, i.e. maximum addition of ethanol through the gas phase.
The ammonia concentration in the liquid phase is calculated by:
C C − 0.2C
(132 / 2) (g/L) (5-67)
N
=
N 0 x
⋅
This is derived from D(C N0 -C N ) = 0.2 μ C x at steady state. At steady state, oxygen
consumption equals oxygen mass transfer rates, then the DO level is determined by
coupling Equations (5-59a) and (5-59b):
*
DO = C = C − Q k a
(5-68)
o O O
/
2
2
2
L
The ammonia concentration remains higher than 1.7 g/L for all dilution rates up to
0.32 h -1 due to the continual addition of the fresh medium at a level (C n0 = 2.0 g/L)
which is sufficient for the cells’ growth. The DO values are higher than 4 mg/L for
steady state operations ( μ < 0.32h
−1
). When the dilution rate is higher than 0.32 h
-1 , the
cells are washed out and the DO is the same as the maximum dissolved oxygen in the
medium solution (7.0 mg/L).
The results in Figure 5-14a predict that both the ammonia and oxygen are
sufficient to support the steady state operations at all dilution rates up to 0.32 h -1 . When
the dilution rate is greater than 0.32 h -1 , the cells are washed out so there is no demand
for oxygen and ammonia. We can conclude that the dilution rate should not be set too
low or too high for steady state operation in the continuous removal of ethanol from
polluted air. Figure 5-14b shows the predicted results of biomass (X) and substrate
(ethanol, C e ) concentrations, and dissolved oxygen level (DO) at higher ethanol addition
rates, i.e.
y e in
=
,
0.14D(
V / Q)
. The DO level decreases as dilution rates increase.
When the dilution rate is higher than 0.1 h
-1 , DO declines to a level that is below the
133