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EPA 540/S-93/505
Pilot-Scale Demonstration of a Two-Stage
Methanotrophic Bioreactor for Biodegradation of
Trichloroethene in Groundwater
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Pilot-Scale Demonstration of a Two-Stage Methanotrophic
Bioreactor for Biodegradation of Trichloroethene in Groundwater (155K)
ABSTRACT
Pilot-Scale Demonstration of a Two-Stage
Methanotrophic Bioreactor for Biodegradation of
Trichloroethene in Groundwater
Emerging Technology Summary
EPA 540/S-93/505
October 1993
BioTrol, Inc., Eden Prairie, Minnesota, developed an above-ground biological
remedial system for water contaminated with halogenated volatile organic compounds,
including trichloroethylene (TCE) and related chemicals. The Methanotrophic
Bioreactor is innovative because it has design features that circumvent problems
peculiar to treatment of this class of chemicals. BioTrol uses a specific organism
(Methylosinus trichosporium OB3b, or simply OB3b) that oxidizes TCE rapidly
and utilizes methane, an abundant and inexpensive source of carbon, as its growth
substrate. BioTrol also incorporates a two-stage reactor to first grow the microorganisms
(culture vessel) and then supply them to a second stage contact reactor (plug
flow) where conditions allow volatile TCE to remain in the liquid phase. The
technology is applicable to water contaminated with halogenated aliphatic hydrocarbons,
including TCE, dichloroethylene isomers, vinyl chloride, dichloroethane isomers,
chloroform, dichloromethane, and others. The first stage of the Methanotrophic
Bioreactor involves the propagation of OB3b on methane in a 400-L continuous-flow
suspended growth culture vessel. Methane transfer efficiency to the culture
vessel was improved by addition of a circulating gas-saturation device. Cells
grown in the culture vessel are supplied to the plug flow contactor where the
culture medium is mixed with the contaminated water. OB3b microorganisms are
capable of degrading TCE in the absence of methane. This is important because
TCE is extremely volatile, and bubbling of methane through the reaction vessel
would likely result in stripping of TCE from the water. The plug flow bioreactor
consists of 100 ft of 2-in stainless steel pipe fitted with stainless steel
sample ports every 20 ft. The specific objectives of the pilot demonstration
were to test the scale-up potential of a bench system and determine the economic
feasibility of the technology based on operating costs at pilot scale. In 1993,
six thousand gallons of air-stripped (previously TCE-contaminated) groundwater
were shipped to, and stored at, BioTrol's pilot-testing facility in a stainless
steel tank trailer. Water was piped into a 500-gal polyethylene surge tank,
and then pumped at a rate of 1 L/minute into the plug-flow reactor. TCE was
metered into the ground water within the enclosed reactor system to achieve
an influent TCE concentration of 2 ppm. OB3b cell culture was fed from the culture
vessel to the plug flow reactor at a rate of 0.1 L/minute. The reactor was periodically
sampled throughout its length and the water was analyzed for TCE. The results
from this pilot test show that TCE could be reduced within the reactor by 87.6%
to less than 0.155 ppm. Estimated methane costs for the study were $0.33/1000
gal of water treated. BioTrol claims that system modifications could potentially
reduce this component of treatment.
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Posted February 26, 1999
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