Experimental Study of Biodegradation of Ethanol and Toluene Vapors

Two more independent experiments were conducted at different benzyl alcohol
feed rates of 0.34 and 0.46 g/h (See Figures 4-19 and 4-20). When benzyl alcohol was
added at feed rates of 0.34 and 0.46 g/h at an inlet toluene concentration of 4.5 mg/L,
the toluene concentrations in the outlet gas increased to 0.21 and 0.45 mg/L, which
resulted in toluene removal efficiencies of 95 % and 90 %, respectively. There was no
detectable benzyl alcohol in the liquid, and the toluene liquid concentration remained at
15 mg/L for these two cases. However, benzoic acid was detected in the liquid phase
(identified by GC-MS, Model VG70VSE, VG Analytical). Benzoic acid in the liquid
phase reached concentrations up to 0.6 and 1.6 g/L for benzyl alcohol feed rates of 0.34
and 0.46 g/h, respectively.
In these cases, benzyl alcohol was partially oxidized to
benzoic acid instead of being completely converted to biomass due to oxygen depletion
when benzyl alcohol feed rates reached 0.34 g/h. Dissolved oxygen measurements
indicated a value of 0 mg/L. When the benzyl alcohol feed rates were increased (e.g,
0.34 g/h), the bacteria in the reactor required more dissolved oxygen for their growth.
Oxygen depletion caused this change of bioremediation mechanism in the
toluene/benzyl alcohol pathways, which will be further discussed in Section 5.6. This
demonstrates that a benzyl alcohol feed rate above 0.34 g/h represents too high of a
metabolic load for Pseudomonas putida due to oxygen limitation and no new steadystate
operating condition could be achieved.
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