Experimental Study of Biodegradation of Ethanol and Toluene Vapors

combustion provides 70 to 90% air purification efficiency at space velocity ranging
from 3200 to 30000 h -1 (Chuang et al., 1992; Carno et al., 1996).
2.2 Bioremediation of VOCs
Biological treatments of VOCs have been reviewed by different workers (Bohn,
1993; Van Groenestijn and Hesselink, 1993; Edwards and Nirmalakhandan, 1996). For
the biological removal of contaminants from waste gases the contaminants have to be
transferred from the gas phase to the liquid phase surrounding the microorganisms or
directly to a biofilm. The driving force for this mass transfer depends on the
concentration in the gas phase, the air/water partition coefficient and the concentration
in the aqueous phase surrounding the microorganisms (Hartmans, 1997). Therefore,
there are three important parameters determining if biological waste gas treatment is
feasible: 1) the pollutant concentrations in the treated air, 2) the air/water partition
coefficient of the contaminant, 3) the kinetics of the microorganism(s) degrading the
contaminant of interest. Various bioreactor designs have been utilized to degrade VOCs
in waste gases including biofilters, trickle beds, and bioscrubbers.
2.2.1 Biofiltration
Biofiltration is the oldest and most widely used of the biological air purification
techniques. In biofiltration, the gas to be treated is forced through a bed packed with
material on which microorganisms are attached as a biofilm. Biodegradable volatile
compounds are adsorbed by the bed material and the biofilm, and subsequently
biologically oxidized into biomass, CO 2 and H 2 O. Usually, the packing material is a
mixture of a natural fibrous substance with a large specific surface area and a coarse
11