Experimental Study of Biodegradation of Ethanol and Toluene Vapors

3.4 Experimental Procedures
Figure 3-1 is a schematic of the experimental apparatus used throughout this
investigation. Air stripping and bioremediation experiments were all performed at 25
ºC in a 3 L, baffled New Brunswick Scientific Bioflow III well-mixed bioreactor at a
working volume of 1.5 L. One six-blade Rushton impeller was positioned 3.5 cm from
the bottom of the vessel. For biodegradation investigations, air was normally supplied
through two, metered inlet streams. All air flowmeters were calibrated using a Wet Test
flowmeter and the calibration curves are given in Appendix B (See Figure B-8). In
order to obtain the desired gas inlet concentration of ethanol or toluene, one air stream
passed through a bubbler filled with either ethanol or toluene which was maintained in a
water bath at 21.0 ± 0.5 ºC; the other stream by-passed the bubbler. These two air
streams were then mixed downstream of the bubbler and directly entered the bioreactor.
In this way, the concentration of ethanol or toluene entering the bioreactor could be
precisely controlled. In some runs, a third stream was employed which passed through
a second bubbler. Thus, ethanol and toluene could be simultaneously added to the
bioreactor. For continuous runs, fresh sterile nutrient media was pumped into the
bioreactor and spent fermentation broth was removed at identical flowrates.
3.4.1 Mass Transfer
Mass transfer studies of toluene and ethanol from contaminated air streams to
the liquid phase, along with oxygen mass transfer studies, were carried out using a
standard stirred tank bioreactor (model GF0014, Chemap AG, Switzerland). The liquid
volume used was 12 liters and the operating temperature was maintained at 25 ± 0.5 o C
for all runs. The general specifications of the reactor are presented in Table C-1. The
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