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MTBE Poster
Session
Evaluation
of MTBE Remediation Options
Rula A. Deeb, Ph.D., and Michael C. Kavanaugh, Ph.D.,
P.E., Malcolm Pirnie, Inc.
MTBE poses unique remediation challenges because of its
physical and chemical properties. It is highly soluble in
water, does not sorb strongly to aquifer materials and
exhibits a low tendency to volatilize from groundwater.
Moreover, depending on gasoline release scenarios, MTBE
plumes could extend farther than BTEX plumes ultimately
impacting a larger volume of groundwater. As a result,
concerns have been raised regarding the feasibility of
remediating MTBE-contaminated sites at reasonable costs.
The California MTBE Research Partnership recently
completed a document that provided a critical evaluation
of the effectiveness of existing and emerging remediation
technologies in addressing cleanup challenges resulting
from the presence of MTBE and its byproducts in soil and
water. This report was designed to provide a sufficient
level of detail on conventional and emerging technologies
to allow consultants, underground storage tank (UST)
owners, regulatory personnel, and other interested parties
to address a wide range of UST cleanup problems at MTBE-impacted
sites. The major findings of this report will be presented
here. This work will include a review of the fate and
transport of MTBE following accidental releases of MTBE-blended
gasoline with an emphasis on the relevance of these fate
and transport characteristics on the selection and design
of subsurface remediation strategies. Demonstrated in situ
and ex situ remediation technologies will be evaluated on
a comparative basis. Each technology evaluation will
include a description of the physical and chemical
processes involved, discussions of the effects of
contaminant and site characteristics, and the technology’s
predicted relative effective for MTBE. An overview of
emerging non-traditional technologies that can potentially
replace or enhance conventional technologies will also be
provided. Finally, general remediation cost estimates will
be discussed in an effort to illustrate how the presence
of MTBE can potentially impact the costs of remediating
gasoline-impacted sites.
In
Situ Biological
Destruction of MTBE: Field Engineering Solutions Based on
Lessons Learned from the Lab
Rula Deeb, Malcolm Pirnie, Kate Scow, UC Davis, Lisa
Alvarez-Cohen, UC Berkeley, and Mike Kavanaugh, Malcolm
Pirnie
Groundwater contaminant plumes from recent accidental
gasoline releases often contain the fuel oxygenate MTBE
(methyl tert-butyl ether) together with BTEX compounds
(benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene).
Laboratory studies evaluating substrate interactions
during the aerobic biotransformation of MTBE and BTEX
mixtures by a pure culture, PM1, were recently performed
during the author's post-doctoral tenure at UC Berkeley in
collaboration with scientists at UC Davis and Tyndall Air
Force Base. PM1 is capable of utilizing MTBE, its major
metabolic product tert-butyl alcohol (TBA), and benzene
for growth. In addition, PM1 can degrade high
concentrations of MTBE at rapid rates (50 mg MTBE/g
cells/hr). In laboratory batch experiments, ethylbenzene
and the xylenes were shown to severely inhibit MTBE
degradation by PM1. In addition, toluene and benzene were
preferentially utilized over MTBE in mixtures following
the induction of the aromatic degradation pathway. In
fact, once the degradation of benzene or toluene proceeded
in mixtures with MTBE, the rate of MTBE degradation slowed
significantly and did not increase to projected levels
until benzene and toluene were almost entirely degraded.
This suggests that if subsurface microorganisms behave
similarly to PM1, the bioattenuation of MTBE could be
inhibited in groundwater plumes until MTBE migrates beyond
the BTEX constituents. Furthermore, MTBE degradation in
subsurface environments could be suppressed in the
presence of BTEX compounds due to the potential depletion
of oxygen, alternative electron acceptors, and/or
nutrients during preferential BTEX biodegradation. During
the last two years, a pilot study involving
bioaugmentation with PM1 was initiated at Port Hueneme,
CA, where an MTBE plume extends more than 4000 feet.
Preliminary results from this study are promising and
suggest that PM1 could be very effective in remediating
soil and groundwater at MTBE-impacted sites. No studies
have yet evaluated the effectiveness of PM1 or any other
culture for the remediation of commingled BTEX and MTBE
plumes. In order to circumvent the limitations projected
by the above-mentioned laboratory study, Malcolm Pirnie
has come up with an engineering solution involvinga
creative application of bioaugmentation with PM1 and
biostimulation with an oxygen source. The primary
objective of our proposed engineered system is to
demonstrate that a combination of bioaugmenation with
exogenous MTBE-degraders, and biostimulation with an
oxygen source, is a cost effective remediation strategy at
sites impacted by mixtures of MTBE and BTEX compounds.
Pending positive results from a pilot study in the
planning stages, our proposed technology can be scaled up
and used to remediate groundwater and soil in the vicinity
of contaminant sources.
Biological
Treatment of Methyl tert-Butyl Ether (MTBE)
Contaminated Groundwater
Robert J. Steffan, Ph.D., Scott Drew1, and
Kelly J. McQueeney, P.E., Envirogen, Inc.
MTBE has been used since 1979 as a high-octane gasoline
additive and an oxygenate, and in recent years it has
emerged as a primary groundwater contaminant near gasoline
service stations and terminals. Laboratory studies
revealed that MTBE can be mineralized to CO2 by
propane oxidizing bacteria including strain ENV425 (POB;
Steffan, et al., Appl. Environ. Microbiol. 63:4216-4222,
1997). Additional studies led to isolation of a bacterial
strain, Hydrogenophaga flava ENV735, that can grow
on MTBE as a sole carbon source. We used these findings to
develop both in situ and ex situ approaches for
remediating MTBE-contaminated sites.
For in situ treatment we used propane biosparging at a
service station site in New Jersey. The application
utilized an existing air sparging system to apply a small
amount of propane and air to the contaminated subsurface,
and a small amount of strain ENV425 (17 L) was added to
the aquifer as a seed culture. Propane concentrations were
maintained below the limit of detection throughout the
treatment, and it was not detected in SVE system off gas.
MTBE concentrations in groundwater (initially 100 to 300
mg/L) were reduced by more than 90% down gradient of the
injection system during 6 months of system operation. The
system is currently being optimized to treat an on site
MTBE source area. A second demonstration of the technology
is ongoing at Port Huenume, CA as part of the EPA’s MTBE
Treatment Technology Certification Program.
For ex situ treatment, strain ENV735 was used to inoculate
both a membrane bioreactor (MBR) and a fluid bed
bioreactor (FBR). The MBR has treated high MTBE
concentrations (to > 2000 mg/L), whereas the FBR has
been used to treat lower concentrations (10 to 15 mg/L).
Both reactors simultaneously treated MTBE, TBA, and BTEX
in groundwater to below regulatory limits (5 m g/L).
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