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William B. Kerfoot,
Ph.D., LSP and Angus McGrath, Ph.D.
A system
called C-Sparging™ which uses ozone/air injected periodically
in conjunction with a pulsing pump has been demonstrated to
reduce MTBE from over 1000 ppb to less than 100 ppb in less
than 40 days. The rate of decay was found to be a ten-fold
reduction in monitoring wells located 3 to 7 meters from the
injection point. Monitoring was performed weekly during and
after treatment.
What is C-Sparging™
The KVA
process of C-Sparging™, in situ air stripping with
micro-encapsulated ozone, combines three unit operations
offering a one-two-three punch to knockout MTBE. First, fine
bubbles with a high surface-to-volume ratio are injected into
the saturated zone to extract dissolved MTBE from contaminated
groundwater. Second, ozone contained within the bubble and
thin film around the bubble reacts extremely rapidly to
decompose the MTBE into simple products: alcohols, acetate
and formate. Third, the residual oxygen from the reaction
encourages bioremediation which consumes the breakdown
products and converts them to carbon dioxide (CO2) and water
(H2O).
Ozone
Microsparging is a Patented Technology for In Situ Treatment
of Volatile Organic Compounds (VOCs) in Groundwater
The reaction
rapidly detoxifies groundwater containing MTBE and BTEX
compounds, specifically benzene, to groundwater standards
without producing harmful byproducts. The reaction is
produced with very low ozone
concentrations—molar ratios—compared to VOC concentrations in
groundwater. The technology combines the unit operations of
air stripping and oxidative decomposition in a single process
which can be catalytically accelerated. In the C-Sparge™
process, air and ozone are injected directly into groundwater
through specially-designed spargers to create “microbubbles”
that have very high surface area-to-volume ratio. The Henry’s
Constant which regulates the partitioning of MTBE from aqueous
to gaseous state is about one-tenth that of benzene
derivatives. However, the surface-to-volume ratio increase of
over 30-fold compensates to promote rapid in situ stripping of
MTBE. As the “microbubbles” rise within a saturated column of
groundwater, they extract or “strip” the VOCs from aqueous to
gas partitioning. Upon entering the microbubbles, MTBE and
BTEX compounds react with ozone in the gaseous state or in the
aqueous “thin layer” surrounding the bubble to decompose.
MTBE is rapidly degraded with time. The rate of decay is
similar to that previously reported by Karpel vel Leitner, et.
al. (1994). In both bench-scale testing and field testing,
ozone microbubbles appeared effective in reducing MTBE
concentrations to beyond 90% of original levels (Kerfoot,
2000). Because of the high solubility of ozone, over 10 times
that of oxygen (CRC, 1972), the decomposed ozone leaves behind
elevated dissolved oxygen. The rate of removal has been
sensitive to ozone concentration, pressure, and iron silicate
content.
Site
Specific System Set-up
A single C-Sparger®
master unit with 6 Spargepoints® was installed in two 3-well
groups, 2 to 3 meters apart, upgradient of two monitoring
wells MW-13 (3 meters) and MW-21 (4 meters). The unit can be
installed with a dual-screened recirculation spargewell which
has a lower Spargepoint® or with isolated Spargepoints®. The
depth to groundwater was 2 to 3 meters. The general
construction of a C-Sparge™ well consisted of a 100 mm casing
leading to a 1.5 meter screen with 0.5 meter above the water
table, a blank casing which was bentonite-sealed in the
annular space to prevent short-circuiting, and a lower 1.5
meter screen (10 slot). Alongside this was a 1.5 cm diameter
tubing leading from the wellhead region to a 50 mm microporous
Spargepoint® 46 cm long with a compression fitting situated
below the lower double screen.
The
predominant soil type was gravelly sands. Water table level
occurred at 2 to 3 meters. The predominant contaminated
region extended vertically from 1 to 3 meters deep. The
Spargepoints® were installed at a depth of 10 meters.
Procedure
Documents Quick Results
Initial
results of the treatment were monitored by three indicators:
-
VOC removal
by groundwater sampling from monitoring wells and certified
laboratory analysis;
-
Dissolved
oxygen (D.O.) field determinations on groundwater grab
samples from monitoring wells;
-
Oxidation-reduction potential (ORP) field determinations on
groundwater grab samples;
Groundwater
sampling showed an immediate rise in concentration of MTBE and
benzene due to mixing, followed by a progressive drop in
concentration. The agitation of the groundwater and capillary
pores by the fine bubbles strips adsorbed fractions. The
mixed concentrations are often a better measure of total mass
for treatment than solely the aqueous fraction. The
concentrations of MTBE from monitoring wells placed at 3
meters’ and 4 meters’ distance from the Spargepoint® rose to
1300 and 550 ppb before converging to less than 100 ppb for a
removal efficiency of 99.9% and 99.8%, respectively after 5 ½
weeks of operation. Benzene rose to a high of 4300 ppb before
dropping to below 700 ppb for 99.8% removal efficiency over 5
½ weeks.
The high
solubility of ozone resulted in maintenance of dissolved
oxygen (D.O.) levels from 1 to 3 ppm, despite initial reducing
conditions. ORP conditions over 300 mv usually indicate the
presence of gaseous ozone. Previous site experience (Commerce
City, CO) with petroleum spill treatment showed similar BTEX
removal, but MTBE was a small component of the spill mixture
(EPA, 1998-clu-in-org).
William B.
Kerfoot, Ph.D., is President of K-V Associates, Inc., Mashpee,
Massachusetts, and an LSP.
Angus
McGrath is a principal Geochemist with SECOR International,
Inc., Oakland, California.
U.S.
Patent #5,855,775 & #6,083,407; other U.S and foreign patents
pending.
References
CRC, 1972.
Handbook of Chemistry and Physics, 52nd Edition. The Chemical
Rubber Co., Cleveland, Ohio, p. B-116.
EPA, 1998.
Field Applications of In Situ Remediation Technologies:
Chemical Oxidation. Ozone – Former service station, Commerce
City, CO, Moiety Associates,
http://www.epa.gov/swertio1;
http://clu-in-org.
Karpel vel
Leitner, R.N.K., A.L. Papailhou, J.P. Crove, J. Payrot, and M.
Dore. 1994. “Oxidation at Methyl Tert-Butyl Ether (MTBE) by
Ozone and Combined Ozone/Hydrogen Peroxide.” Ozone Science &
Engineeering. 16:41-54.
Kerfoot, W.B.
2000. Ozone Microsparging for Rapid MTBE Removal. In:
Chemical Oxidation and Reactive Barriers: Remediation of
Chlorinated and Recalcitrant Compounds, Volume C2-6, eds.
G.B. Wickramanayake, A.R. Gavaskar and A.S.C. Chen. Battelle
Press, Columbus, pp. 187-194.
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