Experimental Study of Biodegradation of Ethanol and Toluene Vapors

Figure 5-17 shows the results at a toluene inlet gas concentration of 6 mg/L. The
system is at steady state for dilution rates up to 0.11 h -1 . When the dilution rate is lower
than 0.11 h -1 , the ethanol (C e ) mass concentrations in the liquid phase follow Equation
(5-70). After the dilution rate reaches levels higher than 0.11 h -1 , dissolved oxygen
concentrations are below the critical value. At these conditions, cells are washed out.
Figure 5-18 shows the results at toluene inlet concentration of 7 mg/L. As the dilution
rate increases due to the high level of biomass in the liquid, the DO level drops quickly.
When the dilution rate is higher than 0.09 h -1 , the DO level falls to a level that is lower
than the critical oxygen value (C cr ) and cells are washed out. We can conclude that at
these inlet conditions, the system could only be at steady state for dilution rates up to
0.09 h -1 due to the limitation of oxygen mass transfer. For cases at higher toluene inlet
concentrations (>7 mg/L) or at higher ethanol inlet concentrations, oxygen-enriched air
would be recommended as the oxygen supply for the system to operate at steady state
conditions.
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