15    DEVELOPMENT OF A KINETIC MODEL FOR CONTINUOUS
FLOW BIOREACTOR TREATMENT OF PETROLEUM
CONTAMINATED SOILS
Ronald Britto, Doctoral Candidate
Joseph H. Sherrard, Professor and Department Chairman
Dennis D. Truax, Associate Professor
Department of Civil Engineering
Mississippi State University
Mississippi State University, Mississippi 39762
INTRODUCTION
Significant quantities of petroleum compounds are released into the soil environment, either
from leakages of underground storage tanks (USTs) or due to accidental spills. The EPA has recently
reported that 100,000 UST leaks have been identified, and that the number might triple in the next
several years.' Profiles of Army USTs, which are leaking, based on construction material, capacity,
age and content have shown just how complex it will be to evaluate and undertake cleanup processes.2
The application of biological processes in controlling environmental problems has increased
strongly during the past decade. A characteristic and important aspect of biological processes is the
feature that pollutants are degraded into products which are part of natural cycles. The generation of
more fundamental knowledge on microbiological degradation, and kinetics involved therein, offers
the possibility of broadening the field of application, especially for degrading non-easily biodegradable pollutants. This creates the opportunity of developing biological methods for the treatment of
hazardous and toxic wastes.3,4
The biological detoxification of hazardous wastes is still largely an underdeveloped technology,
even though biological treatment of hazardous substances has been shown to be a viable option.
Bacterial species are known to possess a variety of detoxification skills. Single bacterial species may
not have the ability to convert a toxicant to carbon dioxide and water. However, a consortium of
bacteria and fungus can.5 Further, it is possible to use naturally occurring microorganisms and to
enhance their activity by modifying and controlling the environment. Specially developed microorganisms have not been shown to be necessary in all cases.6 For example, biodegradation has been shown
to be a very effective cleanup technique for gasoline components in contaminated soils. At 20°C in a
well-mixed, aerated environment, the U.S. EPA priority pollutant gasoline components tested, with
the exception of benzene, were reduced to below detection limits (LOD = 1.0 ppb) within 6.8 hours in
all respirometer vessels tested using the indigenous microbial flora. For benzene, concentrations were
reduced more than 99.9% in the biological test vessels; a 37.5% reduction was observed in the abiotic
control.7
On-site and in-situ bioremediation have been used for the treatment of residues from petroleum
industries. Both these treatment methods are effective, but carry a number of limitations. These
limitations may rise from the difficulty in establishing and maintaining the consortium of microorganisms needed due to problems with supplemental nutrient delivery and mixing. For, example, the
effectiveness of in-situ treatment technologies can experience process limitations due to restrictions of
method and rate of nutrient addition (e.g., oxygen, nitrogen). Removing the soil and treating it above
ground is an alternative which minimizes this limitation. However, these systems are currently operated as batch systems. In this mode, the diverse microbial colony needed to provide effective treatment must establish the appropriate co-metabolism reactions while the size of the population increases
to appropriate levels. Even if effective nutrient addition is achieved, this microbial acclimation to the
waste can take a protracted period of time. Therefore, for this treatment approach to be effective,
virtually all of the contaminated soil must be moved above ground; thereby requiring an extensive
surface area which generally must be enclosed in a manner to restrict intrusion of precipitation.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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