22    EFFECT OF SUPPORT MEDIA ON BIOFILTRATION
OF VOLATILE ORGANIC COMPOUNDS (VOCs)
Zhao Wang, Ph.D. Student
Rakesh Govind, Professor
Department of Chemical Engineering, ML#171
University of Cincinnati
Cincinnati, Ohio 45221
DollofT F. Bishop, ORD
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
INTRODUCTION
Technologies for removal of hazardous pollutants from air have gained increased importance
following the passage of the 1990 Clean Air Act Amendments. Biofiltration is an emerging and
attractive technology for the removal of volatile organic compounds (VOCs) present in air. Traditional VOC removal technologies involve physical or chemical processes such as adsorption,
condensation, thermal incineration or catalytic conversion, etc. Biofiltration involves contacting
a contaminated air stream with biofilms, consisting of active microorganisms immobilized on a
support media. Compared with other treatment methods, biofiltration is low-cost and reliable,
being an ambient temperature process. More importantly, biodegradable VOCs can be degraded
to nonhazardous products such as carbon dioxide and water without the generation of other secondary wastes. It can be applied to any biodegradable VOCs emission problem—from manufacturing and processing units, wastewater and landfill leachate treatment plants, and soil remediation operations.
Currently, fundamental knowledge regarding the mechanisms that affect biofilter performance
is limited. Though a wide range of biofilter support media have been used for biofiltration of
VOCs and other air pollutants, the effect of support media has not been systematically studied.
The objective of this work is to study the effect of support media, especially adsorbent media, on
biofilter performance.
BACKGROUND
Support media used in biofilters can be classified into two major groups: natural bioactive
media and synthetic media. In natural media, such as soil, bark, peat and compost, microorganisms are distributed inside the porous media particles. The nutrients needed for biomass growth
and synthesis are usually present naturally in the media. Generally, biofilters using natural media
are packed-beds with high void fraction. Synthetic support media, which is normally inactive biologically, is used to supply the surface for biofilm immobilization. The support media may exhibit strong or weak adsorption for the air contaminants. The shape of the support media may
also be varied.
Early work on biofiltration was mainly concerned with odorous gases.1-3 Natural bioactive
media, such as soil, wood chips, compost, or peat were used as packing media. These materials
were later used for treatment of VOCs.4-8 Although natural support media are relatively inexpensive and easy to obtain, they exhibit several operational disadvantages. Usually, it is important
but difficult to maintain temperature and moisture content in the bed.9 Usually, these media were
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