Experimental Study of Biodegradation of Ethanol and Toluene Vapors

4.4.3 Toluene-ethanol Bioremediation
For this set of experiments, the aqueous nutrients were added to the bioreactor at
150 mL/h (dilution rate of 0.1 h -1 ), ethanol was introduced through an air stream at an
inlet concentration of 15.9 mg/L and at an air flow rate of 0.4 L/min (loading of 254
mg/L-h, see Figure 4-15). Figure 4-15 shows a continuation of a previous operation.
When the operation reached steady state, toluene was introduced into the bioreactor at
an air inlet concentration of 4.5 mg/L (loading of 72 mg/L-h, total loading of 326 mg/Lh).
Ethanol removal efficiency remained at 100% and toluene removal efficiency
reached 89% at steady state conditions. The liquid concentrations of toluene and benzyl
alcohol were below 10 and 70 mg/L (results are not presented in the Figure 4-15),
respectively. After maintaining steady state conditions for 20 hours, the toluene inlet
concentration was increased to 5.8 mg/L while the ethanol inlet concentration was
maintained at 15.9 mg/L and the air flow rate was maintained at 0.4 L/min (toluene
loading of 93 mg/L-h, total loading of 347 mg/L-h). Over the next 20 hours, toluene
concentration in the outlet air stream increased almost three-fold and reached 1.2 mg/L
which represented a gas removal efficiency of 79 % (See Figure 4-16). However, the
liquid phase ethanol concentration increased to 0.47 g/L and the benzyl alcohol
concentration steadily climbed to 0.12 g/L. This was due to oxygen depletion since
dissolved oxygen reading fell to zero. This will be further discussed in Section 5.6.
Since ethanol is volatile and therefore difficult to supply as a co-substrate, benzyl
alcohol was next introduced in the liquid feed as another potential co-substrate.
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