Experimental Study of Biodegradation of Ethanol and Toluene Vapors

eactor consists of two turbine impellers, which were adjustable in height, and four
evenly spaced baffles (size of 32.5 x 4.5 cm) which ensured that the fluid was
thoroughly mixed. The impeller shaft was driven by a variable speed electric motor.
Gas entered the reactor through a sparger (with 12, 2 mm diameter holes) located at the
bottom of the tank, and its flowrate was measured using a mass flowmeter (Model 8891,
Sierra Instruments, Inc.).
3.4.1.1 Mass Transfer of Ethanol and Toluene
For bioremediation to occur, VOCs need to first be absorbed from the
contaminated air into the fermentation media. The polluted air stream was obtained by
passing air at certain flow rate through a bubbler filled with either ethanol or toluene
which was maintained in a water bath at 21.0 ± 0.5 ºC. In initial studies, this air steam,
containing known concentrations of ethanol or toluene, was then bubbled through sterile
media in the bioreactor at known gas (air-ethanol or air-toluene) flow rates and impeller
speeds. The build-up of ethanol or toluene in the aqueous media was measured by GC
analyses and samples were taken of the effluent air stream to confirm species mass
balances. The collected data were used to determine mass transfer coefficients for
absorption.
3.4.1.2 Effect of Ethanol Addition on Oxygen Mass Transfer
Oxygen transfer from air to an aqueous phase is frequently the rate-limiting step
in aerobic fermentations due to the low solubility of oxygen in water. The effect of
ethanol addition on oxygen mass transfer was conducted using the same reactor as
mentioned above. The first step in conducting the measurements of oxygen transfer to
the aqueous phase in the bioreactor involved deaerating the liquid using nitrogen gas.
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