5    EVALUATION OF ANAEROBIC TREATMENT FOR
BIOREMEDIATION OF PESTICIDE CONTAMINATED SOIL
Thomas E. White, Chief Engineer
Fred G. Herndon, Environmental Scientist
Ciba-Geigy Corporation
Corporate Environmental Technology
Greensboro, North Carolina 27419
INTRODUCTION
The pesticides DDT (l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane) and BHC (hexachlorocy-
clohexane) were widely used for several decades for control of agricultural pests and domestic
insects before being banned in most western countries.1"3 Disposal of wastes and bulk by-products associated with the manufacture and formulation of these chemicals resulted in soil, sediment, and aquifer contamination that is now the focus of corrective action. Cleanup of pesticide
contaminated sites usually involves excavation and thermal treatment of soil which exceeds
health-based levels. For those areas with low contaminant levels, or where it is technically impractical to excavate the soil, in situ technologies are evaluated to achieve prescribed groundwater cleanup standards. In situ treatment options include solidification or stabilization, solvent extraction, vapor extraction, soil flushing, and bioremediation, among others. Ex situ treatment of
pesticide contaminated soil using these technologies may be practical in some cases, specifically
where the level of contamination is moderate.
The present study was conducted to investigate the potential of using adapted anaerobic cultures for remediation of low to moderate levels of DDT and BHC soil contamination. Work by
many investigators has demonstrated that DDT and BHC can be co-metabolicly biodegraded.4"7
The most important metabolites of DDT degradation are DDD (l,l-dichloro-2,2-bis
(p-chlorophenyl)ethane) which is formed by reductive dechlorination of DDT under anaerobic
conditions, and DDE (2,2-bis(p-chlorophenyl) 1,1-dichloroethene) formed by oxidative dehy-
drochlorination of DDT. BHC degrades anaerobically through a series of dehalogenation reactions to 3,4,5,6-tetrachloro-l-cyclohexene and lesser chlorinated compound intermediates such
as dichlorobenzene and trichlorobenzene.4-7-8 Available evidence suggests that BHC can be completely dechlorinated under anaerobic conditions, but the end products of carbon metabolism are
not found.7 DDT can be mineralized by sequential anaerobic-aerobic treatment if the metabolites
of anaerobic treatment are sufficiently dechlorinated.4-9 The critical step in this process appears
to be dechlorination of DDD.
MATERIALS AND METHODS
Two anaerobic DDT biodegradation experiments, and one anaerobic BHC biodegradation experiment, were conducted using serum bottle slurry reactors containing low to moderately contaminated soil. These reactors were operated as batch systems with semi-continuous addition of
substrate. In a separate experiment, an anaerobic soil column reactor with moderate to high concentrations of DDT was operated for 8 months with periodic additions of inoculum. The soil column reactor leachate was recycled continuously for control of soil moisture and delivery of substrate, nutrients, and inoculum. All experiments were conducted at ambient temperature to
simulate anticipated field conditions.
The soils used for the DDT slurry reactor experiments had high clay content. Concentration of
total DDT products (DDT, DDD, and DDE) in these soils ranged from 109 mg/kg to 334 mg/kg.
The soil used for the BHC degradation study was a silty clay with 105 mg/kg of BHC isomers,
50th Purdue Industrial Waste Conference Proceedings, 1995, Ann Arbor Press, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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