Section Five
WASTE TREATMENT PROCESSES
B. BIOLOGICAL
41    VAPOR PHASE BIOREACTOR EVALUATED FOR
PERFORMANCE IN DEGRADING AROMATIC
COMPOUNDS WITH NOVEL PSEUDOMONAS
Barbara Vaughn, Research Assistant, Environmental Engineering
Warren Jones, Assistant Professor, Civil Engineering
James Wolfram, Associate Director at M.S.U., INEL
Center for Biofilm Engineering
Montana State University
Bozeman, Montana, 59717
INTRODUCTION
VOC emissions are subject to increasingly strict regulations dictating a need for innovative, cost-
effective control technologies. Microbial degradation is an effective alternative particularly when the
pollutant concentration is low and the volumetric flow rate is high which is often the case in odorous
or toxic waste gas emissions.1 The degradation of volatile, higher molecular weight organic compounds such as those in the BTEX group are of special interest due to their association with hydrocarbon fuel spills. Some bacteria are capable of metabolizing these contaminants as their sole carbon and
energy source and the one used in this study, Pseudomonas putida Idaho, has been shown to be
resistant to high concentrations of z»-xylene.2
Vapor phase bioreactors offer several advantages over suspended cell systems for contaminant
removal including continuous degradation, high volumetric reaction rates, reduced VOC stripping
losses, and simplified downstream processing.2,3 Because they can operate as a semi-closed system,
bacterial strains can be introduced that target degradation of specific pollutants without competition
from indigenous soil or water microorganisms.4
Before vapor phase bioreactors can be adequately developed, fundamental studies are needed to
optimize reactor design and operation. The goal of this research was to evaluate the performance of
vapor phase bioreactors in response to various process parameters in order to produce a maximum
feed rate to reactor volume ratio and a minimum of contaminant breakthrough. The elimination
capacity of two reactors with different packings was compared by varying gas and liquid flow rates
and influent vapor phase xylene concentrations.
An important step in the application of this technology is to derive and validate mathematical
models of the process for predictive and scale-up calculations. Information from the current study
will be used to help calibrate and refine a model being developed at Montana State University.
BACKGROUND
The project evolved from work done at Idaho National Engineering Laboratory (INEL) involving
isolation of microorganisms with the ability to use methylated aromatics, such as xylene and toluene,
as their sole carbon source. INEL collected and screened several petroleum-contaminated soil and
water samples for organisms that could degrade toluene, xylenes, and pseudocumene. Chemostats
were used to maintain continuous cultures under conditions of controlled aeration and pH. Initially,
toluene or p-xylene was introduced via vaporization. Cells grew to a density of 108-109 cells/mL and
survived under continuous feed conditions for three years. One isolate was not only tolerant to high
concentrations of toluene and p-xylene but utilized these compounds as its sole carbon source and
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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