Experimental Study of Biodegradation of Ethanol and Toluene Vapors

4.4 Continuous Bioremediation
4.4.1 Ethanol Bioremediation
Pseudomonas putida was initially grown in a batch culture which contained an
initial dissolved ethanol concentration of 2.6 g/L. After 11 hours, when the ethanol was
completely consumed and the biomass concentration reached a certain level, the
medium pump was started at a flow rate of 150 mL/h (dilution rate of 0.1 h -1 ) and
ethanol was continuously added at an air inlet concentration of 15.9 mg/L and flow rate
of 0.37 L/min (ethanol loading of 235 mg/L-h). Figure 4-11 demonstrates that the
ethanol transferred from the polluted air stream was continuously utilized by
Pseudomonas putida. After operating for 25 hours, the inlet ethanol concentration was
increased to 19.5 mg/L (air flow rate to 0.39 L/min accordingly; ethanol loading of 304
mg/L-h). The bioreactor was again operated at steady state for another 25 hours before
shutting down the bioreactor in order to study other operating conditions. During the
steady state operations, there was no ethanol detected from the outlet gas stream.
Figure 4-12 shows the results for another independent continuous run. After
operating for 38 hours at an inlet ethanol concentration of 15.9 mg/L and air flow rate
of 0.37 L/min (ethanol loading of 235 mg/L-h), the ethanol inlet concentration was
increased to 25.0 mg/L and the air flow rate was increased to 0.42 L/min (ethanol
loading of 420 mg/L-h). The biomass concentration and the media pH started to
decrease while acetic acid was detected in the liquid phase (identified by GC-MS,
Model VG70VSE, VG Analytical). Dissolved oxygen indicated a value of 0 mg/L at
this condition. Instead of being completely converted to biomass, ethanol was only
partially converted to acetic acid and then excreted into the media when the inlet
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