U.S. patent application number 11/054582 was filed with the patent office on 2005-09-01 for in-situ surfactant and chemical oxidant flushing for complete remediation of contaminants and methods of using same.
Invention is credited to Shiau, Bor-Jier.
Application Number | 20050191131 11/054582 |
Document ID | / |
Family ID | 28044706 |
Filed Date | 2005-09-01 |
United States Patent
Application |
20050191131 |
Kind Code |
A1 |
Shiau, Bor-Jier |
September 1, 2005 |
In-situ surfactant and chemical oxidant flushing for complete
remediation of contaminants and methods of using same
Abstract
The present invention relates to removal of subsurface
contaminants and methods of same. In more particular, but not by
way of limitation, the present invention relates to an integrated
method for remediating subsurface contaminants through the use of a
low concentration surfactant solution (and methods of making and
using novel surfactant solutions) followed by an abiotic polishing
process to thereafter achieve a substantially reduced subsurface
contaminant concentration that surfactant flushing alone cannot
achieve.
Inventors: |
Shiau, Bor-Jier; (Norman,
OK) |
Correspondence
Address: |
DUNLAP, CODDING & ROGERS P.C.
PO BOX 16370
OKLAHOMA CITY
OK
73113
US
|
Family ID: |
28044706 |
Appl. No.: |
11/054582 |
Filed: |
February 9, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11054582 |
Feb 9, 2005 |
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10290424 |
Nov 6, 2002 |
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6913419 |
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60333244 |
Nov 6, 2001 |
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Current U.S.
Class: |
405/128.15 ;
405/128.5; 405/128.7 |
Current CPC
Class: |
B09C 1/08 20130101; B09C
2101/00 20130101; B09C 1/002 20130101; B09C 1/02 20130101 |
Class at
Publication: |
405/128.15 ;
405/128.5; 405/128.7 |
International
Class: |
B09C 001/00 |
Claims
What is claimed:
1. A method for substantially removing subsurface contaminants,
comprising the steps of: introducing an effective amount of at
least one preselected surfactant solution; and introducing an
effective amount of at least one preselected chemical oxidant,
wherein the effective amount of the at least one preselected
surfactant in combination with the effective amount of the at least
one preselected chemical oxidant are capable of substantially
removing subsurface contaminants.
2. The method of claim 1, wherein the effective amount of the
preselected subsurface contaminant is introduced first and the
effective amount of the at least one preselected chemical oxidant
is introduced second.
3. A method for substantially expediting subsurface remediation of
contaminants comprising the steps of: introducing at least one
surfactant capable of remediating at least one subsurface
contaminant and sequentially introducing at least one preselected
chemical oxidant.
4. The method of claim 3, wherein, in the step of introducing at
least one surfactant solution capable of remediating at least one
subsurface contaminant and sequentially introducing at least one
preselected chemical oxidant, the preselected chemical oxidant is
introduced by the method of injection.
5. The method of claim 3, wherein the subsurface contaminant is a
dense non-aqueous phase liquid.
6. The method of claim 3, wherein the subsurface contaminant is a
light non-aqueous phase liquid.
7. The method of claim 1, wherein the preselected surfactant
solution is selected from the group consisting of an anionic
surfactant, a cationic surfactant, a nonionic surfactant or any
combinations thereof and one or more combinations thereof.
8. The method of claim 7, wherein the preselected surfactant
solution is a mixture of sodium dioctylsulfosuccinate and sodium
dihexylsulfosuccinate.
9. The method of claim 7, wherein the preselected surfactant
solution is a mixture of sodium dioctylsulfosuccinate and
polyoxyethylene sorbitan monooleate.
10. The method of claim 7, wherein the preselected surfactant
solution is a mixture of sodium dioctylsulfosuccinate and linear
alkyl diphenyloxide disulfonate.
11. The method of claim 7, wherein the preselected surfactant
solution is a mixture of alkylamine sodium sulfonate and sodium
dihexylsulfosuccinate.
12. The method of claim 1, wherein the effective amount of the at
least one preselected chemical oxidant is a free radical.
13. The method of claim 12, wherein the effective amount of the at
least one preselected chemical oxidant is selected from the group
consisting of hydrogen peroxide, potassium permanganate, and
combinations thereof.
14. The method of claim 1, wherein the wt % of effective amount of
the at least one preselected surfactant solution is in a range from
about 0.05% to about 15%.
15. The method of claim 1, wherein the wt % of effective amount of
the at least one preselected surfactant solution is in a range from
about 3% to about 8%.
16. The method of claim 1, wherein the wt % of effective amount of
the at least one preselected surfactant solution is in a range from
about 1% to about 3%.
17. The method of claim 1, wherein the wt % of effective amount of
the at least one preselected surfactant solution is in a range from
about 0.05% to about 1%.
18. The method of claim 1, wherein the effective amount of the at
least one preselected surfactant solution is anionic.
19. The method of claim 1, wherein the effective amount of the at
least one preselected surfactant solution is nonionic.
20. An abiotic process for polishing at least one surfactant
remediated subsurface contaminant in order to further remediate at
least one subsurface contaminant to substantially undetectable
levels, comprising the step of introducing an effective amount of
at least one preselected chemical oxidant capable of degrading the
remaining at least one of subsurface contaminant to substantially
undetectable levels.
21. The process of claim 20, wherein the effective amount of the at
least one preselected chemical oxidant is introduced by the method
of injection.
22. The process of claim 20, wherein the subsurface contaminant is
a dense non-aqueous phase liquid.
23. The process of claim 20, wherein the subsurface contaminant is
a light non-aqueous phase liquid.
24. The process of claim 20, wherein the effective amount of the at
least one preselected chemical oxidant is a free radical.
25. The process of claim 20, wherein the effective amount of the at
least one preselected chemical oxidant is selected from the group
consisting of hydrogen peroxide, potassium permanganate, and
combinations thereof.
26. A method for substantially removing subsurface contaminants,
comprising the steps of: introducing an effective amount of at
least one preselected surfactant solution, including the steps of:
determining the contaminant solubilization of the surfactant
system, determining the surfactant sorption and precipitation of
the surfactant system determining the surfactant non-aqueous phase
liquid behavior properties of the surfactant system to assess the
potential for surfactant losses under subsurface conditions, and
performing contaminant extraction-column studies to simulate flow
through conditions in the aquifer; introducing an effective amount
of at least one preselected chemical oxidant, including the steps
of: determining relative reaction rates of the reactant,
determining the life span of the reactant, evaluating the chemical
demand associated with pH adjustment, and identifying geochemical
characteristics of the site; wherein the effective amount of the at
least one preselected surfactant in combination with the effective
amount of the at least one preselected chemical oxidant are capable
of substantially removing subsurface contaminants.
27. The method of claim 26, wherein the effective amount of the
preselected subsurface contaminant is introduced first and the
effective amount of the at least one preselected chemical oxidant
is introduced second.
28. A method comprising the steps of determining chemical addition
ratios and reaction times for a chemical oxidation system based on
the following data: reaction kinetics; pH conditions; naturally
occurring interference within the subsurface of the specific site;
and mobility control of the injected oxidant to the targeted
area.
29. A subsurface contaminant site substantially remediated by the
process comprising the steps of: introducing an effective amount of
at least one preselected surfactant solution; and introducing an
effective amount of at least one preselected chemical oxidant,
wherein the effective amount of the at least one preselected
surfactant in combination with the effective amount of the at least
one preselected chemical oxidant are capable of substantially
removing subsurface contaminants.
30. The substantially remediated site of claim 29, wherein the
effective amount of the preselected subsurface contaminant is
introduced first and the effective amount of the at least one
preselected chemical oxidant is introduced second.
31. The substantially remediated site of claim 30, wherein the
preselected surfactant solution is selected from the group
consisting of an anionic surfactant, a cationic surfactant, a
nonionic surfactant or any combinations thereof and one or more
combinations thereof.
32. The substantially remediated site of claim 30, wherein the
preselected surfactant solution is a mixture of sodium
dioctylsulfosuccinate and sodium dihexylsulfosuccinate.
33. The substantially remediated site of claim 30, wherein the
preselected surfactant solution is a mixture of sodium
dioctylsulfosuccinate and polyoxyethylene sorbitan monooleate.
34. The substantially remediated site of claim 30, wherein the
preselected surfactant solution is a mixture of sodium
dioctylsulfosuccinate and linear alkyl diphenyloxide
disulfonate.
35. The substantially remediated site of claim 30, wherein the
preselected surfactant solution is a mixture of alkylamine sodium
sulfonate and sodium dihexylsulfosuccinate.
36. The substantially remediated site of claim 29, wherein the
effective amount of the at least one preselected chemical oxidant
is a free radical.
37. The substantially remediated site of claim 33, wherein the
effective amount of the at least one preselected chemical oxidant
is selected from the group consisting of hydrogen peroxide,
potassium permanganate, and combinations thereof.
38. The substantially remediated site of claim 29, wherein the wt %
of effective amount of the at least one preselected surfactant
solution is in a range from about 0.05% to about 15%.
39. The substantially remediated site of claim 29, wherein the wt %
of effective amount of the at least one preselected surfactant
solution is in a range from about 3% to about 8%.
40. The substantially remediated site of claim 29, wherein the wt %
of effective amount of the at least one preselected surfactant
solution is in a range from about 1% to about 3%.
41. The substantially remediated site of claim 29, wherein the wt %
of effective amount of the at least one preselected surfactant
solution is in a range from about 0.05% to about 1%.
42. The substantially remediated site of claim 29, wherein the
effective amount of the at least one preselected surfactant
solution is anionic.
43. The substantially remediated site of claim 29, wherein the
effective amount of the at least one preselected surfactant
solution is nonionic.
44. A subsurface contaminant site substantially remediated by the
process comprising the steps of: introducing at least one
surfactant capable of remediating at least one subsurface
contaminant and sequentially introducing at least one preselected
chemical oxidant.
45. The substantially remediated site of claim 44, wherein, in the
step of introducing at least one surfactant solution capable of
remediating at least one subsurface contaminant and sequentially
introducing at least one preselected chemical oxidant, the
preselected chemical oxidant is introduced by the method of
injection.
46. The substantially remediated site of claim 44, wherein the
subsurface contaminant is a dense non-aqueous phase liquid.
47. The substantially remediated site of claim 44, wherein the
subsurface contaminant is a light non-aqueous phase liquid.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
10/290,424, filed Nov. 6, 2002, which claims the benefit under 35
U.S.C. .sctn. 119(e) of U.S. Provisional Application Ser. No.
60/333,244, filed Nov. 11, 2001, entitled "USE OF IN-SITU SEQUENT
AND CHEMICAL OXIDANT FLUSHING FOR COMPLETE REMEDIATION OF
CONTAMINATED SOILS AND GROUNDWATERS", the contents of which are
expressly incorporated herein in their entirety by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to removal of subsurface
contaminants and methods of same. In more particular, but not by
way of limitation, the present invention relates to an integrated
method for remediating subsurface contaminants through the use of a
low concentration surfactant solution (and methods of making and
using novel surfactant solutions) followed by an abiotic polishing
process to thereafter achieve a substantially reduced subsurface
contaminant concentration that surfactant flushing alone cannot
achieve.
[0004] 2. Background Information Relating to the Invention
[0005] Surfactant enhanced subsurface remediation (SESR) is a
unique technology for expediting subsurface remediation of
non-aqueous phase liquids (NAPLs). Studies known to those in the
art have previously evaluated the SESR technology in both
laboratory scale studies and field scale demonstration studies.
Traditionally, the surfactant system in SESR (typically an anionic
or nonionic surfactant), is designed to remove organic contaminants
(including chlorinated solvents) from contaminated the soil.
Surfactant systems significantly increase the solubility of
hydrophobic organic compounds and, if properly designed and
controlled, also significantly increase the mobility of NAPLs. A
significantly reduced remediation time thereby results as well as
increased removal efficiency (up to 3 or 4 orders of magnitude) and
reduced cost of NAPL removal through use of surfactant system for
subsurface remediation.
[0006] Surfactant flushing solutions, typically, can be designed to
be effective under most subsurface conditions. In most cases, the
effectiveness of the surfactant flushing solutions is not reduced
due to the presence of more than one contaminant.
Naturally-occurring divalent cations and salts may affect the
performance of certain surfactants, as well as the removal
efficiency for cationic heavy metals. It is possible, however, to
design an effective surfactant system for removal of the target
contaminants under any of these conditions. A number of factors
influence the overall performance and cost effectiveness of SESR
systems. These factors include: Local ground water chemistry; Soil
chemistry (e.g. sorption, precipitation); Ability to deliver the
surfactant solution to the area of contamination; Surfactant
effects on biodegradation of the NAPL compounds as well as
degradation of the surfactants; Public and regulatory acceptance;
Cost of the surfactant; Recycle and reuse of the surfactant, if
necessary; and Treatment and disposal of waste streams. Bench scale
tests (treatability studies) must be conducted on site specific
soils and NAPL (if available) to ensure the optimal system is
selected for a particular site.
[0007] Surfactant flushing can remove a large portion of the mass
of subsurface contaminant liquid. In general, it is not expected
that surfactant flushing alone will have a high probability of
reducing the subsurface contaminant concentration to a level
necessary to allow the site to be considered "remediated."
Therefore, a treatment train (or integrated) approach is necessary
to speed up or achieve the closure of the site. It is to such an
integrated approach involving a preselected surfactant solution
flush coupled with an abiotic oxidation polishing step and methods
thereof that the present invention is directed.
SUMMARY OF INVENTION
[0008] The present invention is directed to a method for
substantially removing subsurface contaminants through an
integrated approach utilizing a preselected surfactant solution and
a preselected chemical oxidant. Such an innovative integrated
approach satisfies a need in the marketplace for a cost-effective
and less time consuming system to remove substantially all
subsurface contaminants--a level of remediation has been
traditionally unavailable. A method of the present invention
comprises the steps of introducing an effective amount of at least
one preselected surfactant solution and an effective amount of at
least one preselected chemical oxidant. The combination of the
preselected surfactant solution and the preselected chemical
oxidant are capable of substantially removing subsurface
contaminants. Additionally, the present invention relates to a
subsurface contaminated site that is substantially remediated by
this integrated approach and novel surfactant solutions.
DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0009] FIG. 1 is a schematic diagram showing, generally, an
integrated surfactant flushing and treatment system according to
the present invention.
[0010] FIG. 2 is a graphical representation showing the results of
a NAPL removal test in a one-dimensional (1-D) column.
[0011] FIG. 3 is a schematic representation of pre- and
post-surfactant free phase gasoline distribution in a "Shallow
Zone" at an underground storage tank contamination site--i.e.
Carroll's Grocery in Golden, Okla.
[0012] FIG. 4 is a schematic representation of pre- and
post-surfactant flushing/chemical oxidation benzene concentration
distribution methodology of the present invention in a "Shallow
Zone" at an underground storage tank contamination site--i.e.
Carroll's Grocery in Golden, Okla.
[0013] FIG. 5 is a graphical representation showing the results of
a TCE breakthrough test with sequent surfactant and chemical
oxidation flushing in a 1-D column.
DETAILED DESCRIPTION OF INVENTION
[0014] It is to be understood that the invention is not limited in
its application to the details of construction and the arrangements
of the components set forth in the following description (e.g.
texts, examples, data and/or tables) or illustrated or shown in the
drawings. The invention is capable of other embodiments or of being
practiced or carried out in various ways. Also, it is to be
understood that the phraseology and terminology employed herein is
for purpose of description and should not be regarded as limiting
and one of ordinary skill in the art, given the present
specification, would be capable of making and using the presently
claimed and disclosed invention in a broad and non-limiting
manner.
[0015] As used herein, the term "subsurface contaminant" refers to
any organic or inorganic impurity or halogenated solvent (such as a
chlorinated solvent) that is toxic to the underground surface.
Additionally, the term "surfactant solution" refers to any anionic
or nonionic surfactant or cosurfactant combination that is
functionally capable of removing organic or inorganic contaminants
as well as halogenated solvents (such as a chlorinated solvent)
from a contaminated subsurface area, such as subsurface soil or
water systems. Further, the term "oxidant" refers to any oxidizing
agent capable of degrading a contaminated plume or entrapped
residual pollutants whether they are organic, inorganic, or
halogenated solvents. The term "polishing step" as used herein,
refers to the innovative abiotic process of the presently disclosed
and claimed invention that includes the steps of injecting or
introducing predetermined concentrations of a chemical oxidant to
further degrade and reduce the subsurface contaminant subsequent to
a surfactant flushing step. "Integrated approach" as used herein,
refers to a low concentration surfactant flush in combination with
the abiotic polishing step. "Remediation" as used herein, refers to
the substantially complete removal of soil and groundwater
pollutants by various treatments or restoring methods to achieve
the standard set by the responsible regulatory agency for the
particular contaminated subsurfact system (e.g. National Primary
Drinking Water Regulations (NPDWR) for subsurface ground
water).
[0016] Due to certain advantages associated with the use of the
integrated approach of the presently claimed and disclosed
invention, one of ordinary skill in the art will most likely
recognize the benefits of this approach when time is of the
essence. One such advantage is that by using the low concentration
surfactant flush step in combination with the subsequent abiotic
polishing step, a higher probability exists of reducing the
subsurface contaminant concentration to a level necessary to allow
the site to be considered remediated--i.e. substantially all
contaminats have been removed. This process will tend to achieve
minimal pollutant content of the underground surface while
decreasing the time spent as compared to prior art techniques that
utilize a higher concentration surfactant flush as the sole means
of remediating a contaminated site.
[0017] Prior to Applicant's inventive concept, higher concentration
surfactant flushing alone has been the common method of site
remediation. As shown in FIG. 1, the present invention includes an
overall integrated surfactant flushing and treatment system 10. A
pre-determined surfactant solution 20 is prepared in a mixing tank
30. After the surfactant solution 20 is prepared, the
surfactant-NAPL phase behavior is evaluated on-site. If the
surfactant solution 20 meets all criteria set for the
surfactant--NAPL phase behavior, such as optimal microemulsion
(either Winsor Type III or Type I) the surfactant solution 20 is
delivered to a targeted treatment zone 40 via an injection well 50
and a pumping system 60. Removed contaminant and surfactant
solution 70 is extracted from a recovery well 80. The free-phase
oil is separated from the surfactant stream in an oil/water
separator 90. If the contaminant and surfactant solution 70 is pH
sensitive for its recovery, a pH-adjustment tank 100 could be added
before the oil/water separator 90 to reduce the solution pH and
enhance the surfactant separation. From the oil/water separator 90,
a waste stream 110 is sent to an air stripper 120 or other
equipment (such as liquid-liquid extraction) to remove dissolved
volatile organic chemicals (VOC) 130. The waste stream 110 is
delivered to a pre-filtration system 140 to remove the large solid
particle or sediment in the waste stream 110. If surfactant reuse
is required, the waste stream 110 will go through a second
pH-adjustment tank 150 and an ultrafiltration membrane system 160.
Most surfactant micelle phase will be rejected at the retentate
side 170 and sent back to the mixing tank 30 for reuse. The waste
water containing mainly surfactant monomer and trace contaminant
will pass through the ultrafiltration membrane system 160 for final
disposal 180 or sent to a wastewater treatment plant for
treatment.
[0018] As outlined and shown in particular examples hereinafter,
the Applicant's presently claimed and disclosed methodology
demonstrates significant removal of NAPL from a contaminated source
area via remediation. In one embodiment of this invention,
surfactant flushing projects were conducted at a surfactant
concentration ranging between 3 to 8 wt % of surfactant based upon
the total weight of the surfactant solution (e.g. 3 wt % would be
3% surfactant/97% water or other solvent). This range may be
somewhat over-conservative because, within this range of surfactant
concentrations, reuse or reconcentration of the recovered
surfactant typically is necessary to improve the economics of the
overall project. In order to recover/separate the surfactant,
contaminant concentrations must be reduced to acceptable levels in
the surfactant solution and then the surfactant must be
re-concentrated for reinjection. In other embodiments of this
invention, surfactant concentrations in a range from about, 0.05%
to about 15 wt % are contemplated for use. In a most preferred
embodiment of this invention, a lower surfactant concentration,
such as 0.1%, is most desirable. Several advantages of using a low
surfactant concentration, are: (1) significant savings on chemical
use and project cost; (2) minimizing and/or completely eliminating
the reuse and recycling of the recovered surfactant; and (3)
improving the above-ground treatment efficiency (e.g., less
retention time for breaking the macro- or microemulsion during the
oil/water separation stage, and less foaming of surfactant).
Therefore, the ability of lowering the costs of a SESR project,
such as with utilizing a lower surfactant concentration, further
improves the total cost effectiveness for the remediation of sites.
The quantity of surfactant necessary for use with the presently
disclosed and claimed invention is up to one order of magnitude
(from several weight percents reduced to several thousands ppm or
mg/L) less than prior art surfactant flushing systems used for
light non-aqueous phase liquids (LNAPLs) as well as for dense
non-aqueous phase liquids (DNAPLs).
[0019] The surfactant solution of the presently claimed and
disclosed invention may be any anionic, cationic, or nonionic
surfactant or any combinations thereof as well as one or more
combinations thereof. These combinations include, but are not
limited to: anionic surfactant/anionic surfactant; anionic
surfactant/nonionic surfactant; anionic surfactant/cationic
surfactant; nonionic surfactant/nonionic surfactant; and nonionic
surfactant/cationic surfactant combinations, to name but a few of
the possible permentations.
[0020] Further, the present invention encompasses an abiotic
process to address the post-surfactant polishing step to further
enhance site remediation. This abiotic process involves injecting
pre-determined concentrations of chemical oxidant to degrade the
dilute contaminant plume and/or trace entrapped residual
pollutant(s) that remain after the surfactant flushing step. The
effectiveness of these oxidants depends on the types of
contaminants and geological formations found at the site. Thus, the
chemical oxidant is chosen or "predetermined" based on an analysis
of the site: i.e. the functionality of the chemical oxidant must
match or be capable of degrading any remaining contaminants or
pollutants. Thus, one of ordinary skill in the art, given the
present specification, would be capable of selecting an appropriate
chemical oxidant given an identification of the contaminants or
pollutants to be remediated.
[0021] The two most common oxidizing agents used for in-situ
chemical oxidation are hydrogen peroxide and potassium
permanganate, yet various other oxidizing agents including, but not
limited to, sodium permanganate, ozone, chlorine dioxide, or
dissolved oxygen may be used. In the chemical oxidation process
known as Fenton's reaction, injection of hydrogen peroxide is
typically combined with an iron catalyst under reduced pH
conditions to generate powerful hydroxyl free radicals (OH). Since
1934, Fenton's reagent has been recognized as an effective means
for destroying organic compounds in wastewater and most recently as
an in-situ treatment method for soil and groundwater. The dissolved
iron acts as a catalyst for generating the hydroxyl radical,
resulting in free-radical oxidation of the contaminant. A low pH is
necessary to keep the iron in the ferrous state. While the reaction
can be performed successfully at a pH range between 5 and 7, the
performance improves at even lower pH values (as low as 2 to 3).
Obtaining optimal subsurface pH conditions is often limited by the
soil buffering capacity, which is site-specific. For example, if
naturally-occurring carbonates in the soil are high, a significant
acid dose is required to reduce the pH at the site and thereby
improve the performance of the oxidizing agent.
[0022] Potassium permanganate oxidation creates little heat or gas,
therefore contaminant treatment occurs primarily through oxidation.
Potassium permanganate is an oxidizing agent with a unique affinity
for organic compounds containing carbon-carbon double bonds,
aldehyde groups or hydroxyl groups. Under normal subsurface pH and
temperature conditions, the primary oxidation reaction for
perchloroethylene (PCE) and trichloroethylene (TCE) involves
spontaneous cleavage of the carbon-carbon bond. Once this double
bond is broken, the highly unstable carbonyl groups are immediately
converted to carbon dioxide through either hydrolysis or further
oxidation by the permanganate ion. Selection of the proper oxidant
is based on several factors including, but not limited to,
contaminant characteristics, site geochemical conditions, soil
buffering conditions of site, and etc. Fenton's reagent is capable
of oxidizing a wide range of compounds while potassium permanganate
is more selective and is best suited for chlorinated ethene
contaminants such as PCE and TCE. Potassium permanganate often
provides more rapid destruction of specific compounds when compared
to Fenton's reagent, however.
[0023] Previous prior art results from field tests raised concerns
on the effectiveness of using chemical oxidation for contaminated
source zone remediation. Mainly, this was due to the high
concentration of oxidant required, the large amount of heat and gas
released in the subsurface, and the formation of solid-precipitate
at the surface of the contaminant liquid pool. Utilizing the
presently disclosed and claimed methodology, however, the bulk of
the contaminant has been previously removed by surfactant flushing,
followed by a very low concentration (preferrably less than 0.5 wt
%) of oxidant can be used, and the amount of heat generated and the
volume of gas released ceases to be a limiting factor. Using the
methodology of the presently claimed and disclosed invention,
surfactant flushing followed by chemical oxidation is highly
effective for contaminant remediation. Thus, neither surfactant
flushing nor chemical oxidation alone can accomplish substantially,
one hundred percent remediation of a contaminated site. The
combination of surfactant flushing followed by chemical oxidation
does, however, result in a substantially remediated site that had
been contaminated prior to treatment. The presently disclosed and
claimed methodology greatly reduces the long-term risk and
financial burden of the owner of the contaminated site in a site
closure program versus a maintenance-like approach such as
pump-and-treat. The uniqueness of the presently claimed and
disclosed integrated process approach provides significant
improvement on the NAPL clean-up efficiency as compared to the
stand-alone surfactant flushing and stand alone in situ chemical
oxidation for site remediation effort.
[0024] Experiment Methodology
[0025] Surfactant Selection and System Design. Selection of the
proper surfactant system utilizing a series of laboratory screening
tests is one of the most crucial steps in conducting a successful
surfactant flushing project. Laboratory surfactant screening
typically consists of the following tests: contaminant
solubilization tests, surfactant-NAPL phase behavior properties
tests, surfactant sorption and precipitation tests, and contaminant
extraction-column studies. Representative procedures of these tests
are briefly described below. One of ordinary skill in the art,
however, would appreciate the significance and steps necessary to
conduct such tests given the present specification. The purpose of
these tests is to select the best surfactant system for application
at the site--the surfactant is optimized for both the physical and
chemical conditions of the site and the contaminant.
[0026] Contaminant solubilization of NAPL Solubilization tests are
used to determine the solubilization capacity of the surfactant
systems (see e.g. Shiau et al., 1994; Rouse et al. 1993). For a
DNAPL contaminant, the objective of the solubilization test is to
select a surfactant system with ultra-solubilization potential
without mobilizing the NAPL. For a LNAPL contaminant, the optimal
surfactant system is chosen based on mobilization of NAPL under the
ultra-low interfacial tension condition. Typically, surfactant
systems under such conditions will produce a so-called Winsor Type
III (or the middle phase) microemulsion via testing of
surfactant-NAPL phase behavior properties (Shiau et al., 1994). The
solubilization capacity of site-specific NAPL is determined for the
surfactants by two methods: direct visual observation (see Shiau et
al., 1994) and gas chromatography/flame ionization detector
(GC/FID) (i.e., EPA Method 8015 for gasoline range organics (GRO),
diesel range organics (DRO), and other volatile organic chemicals
(VOCs)) and/or gas chromatography/photoionization detector (GC/PID)
measurement (i.e., EPA Method 8021B for BTEX compounds). Direct
visual observation is used as a preliminary screening tool for
various surfactant and NAPL systems. When a proper
surfactant/cosurfactant system is utilized, a middle-phase
microemulsion (a translucent liquid phase intermediate between the
water and NAPL phases) is observed in a mixture of surfactant and
NAPL system.
[0027] Surfactant-NAPL phase behavior properties. The difference
between a microemulsion and macroemulsion (or emulsion) is that a
microemulsion is thermodynamically stable while a macroemulsion is
thermodynamically unstable and will ultimately separate into oil
and water phases. Typically, a macroemulsion of NAPL and surfactant
mixture appears opaque after equilibration. During the
surfactant-NAPL phase behavior testing, equal volume of NAPL and
surfactant solution was added to a batch reactor (at capacity
between 10 mL to 40 mL) and the system was adjusted with salt
(NaCl), hardness (CaCl.sub.2), or cosolvent (short chain alcohols)
to change the hydrophobicity, a crucial parameter to achieve the
optimal surfactant phase behavior, of NAPL and surfactant mixture.
The solution was shaken and left to equilibrate at room temperature
(18.degree. C.) following a 24-hour pre-mixing period. Formation of
a stable middle-phase microemulsion becomes complete within a few
hours to one day. The presence of a middle-phase microemulsion is
confirmed by visual observation (formation of a translucent liquid)
and instrumentation (measuring the ultra-low interfacial tension
(IFT) with a spinning drop tensiometer). (See Cayias et. al, 1975;
Shiau et. al, 2000).
[0028] Sorption, Precipitation, and Phase Behavior Analyses. These
tests assess the potential for surfactant losses under subsurface
conditions (see Shiau et al., 1995 for details). Surfactants can be
lost due to sorption, precipitation, and adverse phase behavior
reactions. Excess surfactant sorbed or precipitated onto soil
inhibits system effectiveness and increases costs. Sorption testing
quantifies the amount of surfactant lost to soil and facilitates a
surfactant comparison analysis. Some surfactants may precipitate or
phase separate due to the presence of salts, divalent cations or
temperature fluctuations. It is essential to ensure that the
surfactant will not precipitate under site specific aquifer
conditions. Surfactant loss due to precipitation and/or phase
separation not only hinders performance but also plugs the aquifer.
Formation of an opaque solution in a mixture of NAPL/surfactant
indicates an adverse phase behavior, which does not provide a
satisfactory sweep efficiency and/or solubilization capacity in the
subsurface.
[0029] Contaminant Extraction-Column Studies. One-dimensional (1-D)
column tests are conducted to simulate flow through conditions in
the aquifer (see Shiau, et al., 2000 for detailed procedures).
Although it is difficult to simulate actual site conditions,
valuable information can be obtained from column studies. This
information includes solubilization enhancement under continuous
flow conditions and head losses during flushing through the
media.
[0030] The results of the column studies aid in the design of pilot
and potential full-scale application designs of the presently
claimed and disclosed inventive methodology. Column test results
are used to quantify the number of pore volumes (PV) required to
mitigate the NAPL for each surfactant system and the polishing
step. Previous laboratory and field studies indicate that the
solubilization mechanism requires 3-15 PV for most NAPL mass
recovery (Shiau, et al. 2000). For the mobilization mechanism, the
required surfactant solution flush is between one to two pore
volumes (PV) to recover the majority of the NAPL mass. From site
soil-packed columns, residual saturation is achieved in the column
by adding the site-specific contaminant(s) to the column (between
0.01 to 0.2 PV) followed by water to remove excess contaminant. A
mass balance of NAPL is determined to estimate the residual
concentration.
[0031] Under low surfactant concentration conditions (<1 wt % of
surfactant), reuse and recycling of surfactant is economically
unnecessary for full-scale implementation. If injection of a higher
concentration surfactant is necessary at the particular site, one
of ordinary skill in the art could use membrane-based systems, such
as Micellar Enhanced Ultrafiltration (MEUF), to recover and reuse
the surfactant. (Lipe et al., 1996; Sabatini et al., 1998b.)
[0032] Chemical Oxidation as a Polishing Step. In the presently
claimed invention and disclosed invention, surfactant flushing is
followed by a polishing stage utilizing the introduction of a
chemical oxidant to substantially degrade the contaminant left in
the soil and groundwater subsequent to the surfactant flushing
step. Bench-scale experiments were conducted to evaluate the
effectiveness of in-situ chemical oxidation in order to illustrate
and evaluate the primary performance characteristics of the
technology, including (1) oxidant-contaminant reaction kinetics,
(2) matrix interactions and other secondary geochemical effects,
(3) subsurface oxidant transport, (4) overall oxidant consumption,
and (5) contaminants treated and overall reductions achieved.
[0033] Chemical Oxidant Selection and System Design. The first step
in the process of chemical oxidant polishing is selecting the
proper oxidant for the site. The two most common oxidants used for
process applications are hydrogen peroxide and potassium
permanganate, however sodium permanganate, ozone, chlorine dioxide,
dissolved oxygen or any other oxidant, in which a person having
ordinary skill in the art may be familiar, may be tested and be
used in this system. To ensure a successful project, several design
steps of a chemical oxidation polishing system must be satisfied.
An understanding of relative reaction rates and the life span of
reactants are required to ensure adequate contact time for the
desired reactions. The chemical demand associated with pH
adjustment must be evaluated since many of the oxidation reactions
are pH-dependant. In addition, geochemical characteristics of the
site must be identified to help predict how naturally occurring
mineral and organic fractions within the soil and ground water will
affect the process.
[0034] Before installing a field-scale chemical oxidation system,
certain data must be collected to ensure proper chemical addition
ratios and reaction times are achieved at the site. This
information may include, but is not limited to, data on the
reaction kinetics, pH conditions, and naturally occurring
interference within the subsurface for the specific site. In
addition, mobility control and transport of the injected oxidant to
the target areas is crucial, especially at a site with less of a
permeability zone and having high organic and mineral
interference.
[0035] Degradation Test. Similar to surfactant screening tests,
bench-scale oxidation degradation studies (i.e., batch tests and
one-dimensional column studies) are performed in the laboratory to
investigate the reaction rates and mechanisms for the previously
discussed oxidants using soils, NAPL (if available), and
contaminated groundwater collected from the demonstration site. In
the laboratory batch tests/kinetic studies, the samples are
prepared in the reactor (e.g., 40 ml EPA vials) spiked with site
contaminants (i.e., LNAPL and/or DNAPL) at the pre-determined
concentrations (from high ug/L to low mg/L). These are the typical
pollutant levels observed at the dilute plume area and/or after
most NAPL mass has been removed from the contaminant source area.
The Fenton's reagent and permanganate constituents required to
promote the respective oxidation reactions were added to the
reactor (e.g., 40 mL vials) at concentrations between 500 mg/L to
ten percent. The samples were equilibrated for various reaction
periods (from hours to days) at the demonstration site groundwater
temperature. The final contaminant(s) and oxidant concentrations
were measured. Changes of reaction parameters, such as pH and redox
potential, Eh, were recorded. The reaction rate constants were
calculated to quantify the removal of contaminant(s).
[0036] In addition, the demand for pH adjustment during chemical
oxidation was evaluated, since many of the reactions involved are
pH dependent. Maintaining the proper pH conditions for Fenton's
oxidation is crucial to the availability of the ferrous ion
(Fe.sup.2+) catalyst. The buffer capacity of the soil determines
whether pH adjustment for chemical oxidation is effective and/or
economical. To evaluate the effects of pH, testing was performed
using potassium permanganate and Fenton's reagent under acidic,
neutral, and basic conditions. Similar batch/kinetic tests for
varying solution pH were conducted as previously described. Soil
and groundwater conditions can affect chemical oxidation
performance through direct competition with contaminants for the
oxidant and should, therefore, be taken into account.
[0037] The primary interference with Fenton's oxidation is
carbonate and bicarbonate, which influence pH conditions and
compete with contaminants for the hydroxyl radical. Elevated soil
organic matters react with Fenton's reagent and potassium
permanganate. Oxidation of heavy metals, such as trivalent chromium
(Cr(III)), remobilize the toxic form of metals like hexavalent
chromium, Cr(VI), and therefore increase the unwanted risk at the
site. If potential risk of remediation of Cr is present, additional
tests are conducted to address these concerns depending on the
selected site conditions (e.g. Cr desoprtion test in the soil peak
columns). Typically, a phased approach is used to streamline the
tests and minimize the number of tests. This can be achieved by
evaluating the degradation rates of the targeted pollutant using
the potential oxidants in a batch experiment. Only those oxidants
with favorable degradation rates will be further investigated on
their consumption rate with the site-specific soil. The chemical
oxidant with minimum mass losses to the soil is thereafter tested
in a one-dimensional column or a two-dimensional sand tank in order
to optimize their conditions for complete degradation of pollutant
in field. The optimal chemical oxidation system is thereafter able
to be selected for the field application and is therefore site
specific or site optimized.
EXAMPLE 1
Sequent Surfactant Flushing and Chemical Oxidation for LNAPL
Remediation--a Gasoline-contaminated Underground Storage Tank (UST)
Site
[0038] A particular gasoline contaminated-site is located in the
southeastern Oklahoma town of Golden. The main contaminant is
gasoline fuel as a result of the leakage of USTs from two former
corner gas stations. Depth to the contaminated zone was 5 to
25-feet. Most free phase LNAPLs were trapped in the shallow zone (5
to 15 ft) containing sandy silt, silty clay, and silt. The treated
area covered approximately 25,000 ft.sup.2. The primary goal of the
project was to remove all free phase gasoline. The secondary goal
was to demonstrate a significant decrease in soil and groundwater
concentrations (one to two orders of magnitude). The tertiary goal
was to see how low the final contaminant concentration in
groundwater could be achieved, to approach the Maximum Contaminant
Level (MCL).
[0039] Before field implementation, Golden site LNAPL, and soil and
groundwater samples were obtained and used to screen for the
optimal surfactant systems. In the laboratory screening
experiments, four anionic surfactant/cosurfactant mixtures were
investigated for their potential use in remediating Golden LNAPL
(fuel gasoline) with the in situ surfactant flushing technology
disclosed and claimed herein. The selected surfactant/cosurfactant
included mixtures of (1) sodium dioctylsulfosuccinate (AOT:75%
active. Aerosol OT 75% PG surfactant, by Cytec Industries, Inc.,
West Paterson, N.J., USA) and sodium dihexylsulfosuccinate (AMA),
(2) AOT and polyoxyethylene sorbitan monooleate (Tween 80), (3) AOT
and linear alkyl diphenyloxide disulfonate (Calfax 16L-35% active,
by Pilot Chemical Company, Santa Fe Springs, Calif., USA), and (4)
Alkylamine sodium sulfonate (Lubrizol DP10052) and AMA. All
surfactant solutions were prepared according to their percent
activity. For example, a 100 g 0.75% AOT solution is prepared by
adding 1 g of AOT raw material (75% active) to 99 g of H.sub.2O
(water). The laboratory screening activities consisted of numerous
tests including surfactant-NAPL phase behaviors, surfactant
sorption and precipitation, and contaminant extraction-column
studies as described previously in the experiment methodology
section (also see Shiau et. al., 1994; Shiau et. al. 1995; Shiau,
et. al. 2000). As shown in Table 1, batch surfactant screening
experiments indicate that all four surfactant mixtures used can
achieve Winsor Type III (middle-phase) microemulsion with Golden
site NAPL, mostly at total surfactant concentration less than 1 wt
%.
1TABLE 1 Summary of Surfactant/NAPL Phase Behaviors NAPL (TPH)
Equilibrated Surfactant Appearance solubility Time of Stable
Concentration of Winsor at optimal Type III Evaluated Type III Type
III Microemulsion.sup.1 Surfactant System wt % Microemulsion system
mg/L (hr) AOT/AMA 1 to 2 transparent 440,000 1 to 2 AOT/Tween 80
0.2 to 1 translucent 400,000 8 to 12 AOT/Calfax16L-35.sup.2 0.2 to
1 translucent 450,000 1 to 2 Lubrizol DP/AMA.sup.3 0.2 to 1 opaque
400,000 8 to 12 .sup.1NaCl (ranging from 0.1 to 3 wt %) was used to
achieve the optimal Type I system at various ratios of surfactant
mixtures .sup.2Surfactant system used at Golden UST site .sup.3A
small portion of the contaminated zone was treated with this
surfactant
[0040] Table IA illustrates the formulation of the preferred
surfactant system AOT/Calfax 16L-35 used at the Golden site for
gasoline clean-up. Also surfactant formulations for other
conatminants, such as disel fuel and TCE, are also listed in Table
IA.
2TABLE IA Cosurfactant Electrolyte Type of Contaminants Surfactant
wt % wt % wt % Microemulsion Gasoline Dioctylsulfosuccinate sodium
linear NaCl Winsor Type III alkyl (AOT) diphenyloxide disulfonate
(Calfax 16L-35) 0.75 0.19 1.2 Diesel Fuel dioctylsulfosuccinate
sodium linear NaCl Winsor Type III alkyl (AOT) diphenyloxide
disulfonate (Calfax 16L-35) 0.75 0.19 1.7 TCE Dioctylsulfosuccinate
sodium linear NaCl Winsor Type III (AOT) alkyl diphenyloxide
disulfonate (Calfax 16L-35) 0.77 0.27 1.84
[0041] The screening tests were conducted at different
surfactant/cosurfactant ratios by adding various amounts of NaCl to
promote the formation of a middle-phase (or Winsor Type III)
microemulsion. In these tests, a low surfactant concentration
(<1 wt %) approach was found to significantly improve the cost
effectiveness of the site clean-up effort. Based on the screening
tests, it was concluded that one surfactant system was the best
candidate for the site-specific conditions (i.e., able to produce a
translucent middle-phase microemulsion with ultra-low interfacial
tension at value<0.005 dyne/cm and the highest NAPL solubility):
a combination of anionic surfactant mixture, AOT/Calfax 16L-35
(total concentration=0.94 wt %) at AOT/Calfax weight ratio of of
0.75/0.01 g with 1.2% NaCl added. The prepared formulation is shown
in Table IA.
[0042] For the polishing step, abiotic chemical oxidation was used
to treat the residual oil and dilute plume at the shallow zone of
this site the Golden site. Both Fenton's Reagent and potassium
permanganate were evaluated. As shown in Table 2, at a low
concentration of chemical oxidant, Fenton's Reagent appeared to be
more favorable in treating the BTEX compounds found at the
site.
3TABLE 2 Representative Results of BTEX Degradation with Fenton's
Reagent Benzene.sup.1 Toluene Ethylbenzene m,p-Xylene o-Xylene
Fenton's % % % % % Reagent Used reduction reduction reduction
reduction reduction H.sub.2O.sub.2 = 2,000 mg/L 92 44 59 47 44
Fe.sup.+2 = 90 mg/L pH = 2 to 3 adjusted by 50% H.sub.2SO.sub.4
H.sub.2O.sub.2 = 2,000 mg/L 93 NA.sup.2 NA NA NA Fe.sup.+2 = 90
mg/L pH = 2 to 3 adjusted by 50% H.sub.2SO.sub.4.sup.2 KMnO.sub.4 =
5,000 mg/L.sup.3 8 NA NA NA NA .sup.1Initial BTEX mixtures
containing 1,000 ug/L of individual compound; reaction time = 12 hr
.sup.2Initial benzene-only concentration = 4,000 ug/L; NA = not
available .sup.3Initial benzene-only concentration = 1,000 ug/L
[0043] For example, 93% of the initial 4,000 .mu.g/L benzene was
degraded using a Fenton's Reagent, containing H.sub.2O.sub.2, 2,000
mg/L, Fe.sup.+2, 90 mg/L, pH value @ 2 to 3. Benzene degradation
was only 8% of the initial 1,000 .mu.g/L benzene after a 5,000 mg/L
KMnO.sub.4 solution was added.
[0044] As shown in Table 3, one-dimensional column tests were
conducted to assess the contaminant removal under hydrodynamic
condition. Injection of a one pore volume of AOT/Calfax (0.94%)
mixture was able to mobilize>90% of the trapped LNAPL from the
1-D column.
4TABLE 3 Summary of 1-D Column Study Results Post-surfactant
Post-surfactant + Total (Step 1) chem oxid (Step 2) contaminant %
contaminant % contaminant removal Process Used removed removed %
Step 1: 91.sup.1 8.6.sup.2 99.6.sup.2 Surfactant: AOT/Calfax (0.94
wt %) + NaCl 1.2 wt % (1PV) Step 2: Fenton's Reagent:
H.sub.2O.sub.2 (0.4 wt %) Fe.sup.+2 (90 mg/L) pH = 2.6
.sup.1Estimated based on the mobilized NAPL volume and dissolved
NAPL data; initial column oil saturation = 2% .sup.2Based on final
soil extraction measurement
[0045] Fenton's Reagent was selected to polish the residual NAPL
after the surfactant flood. Representative column results are shown
in FIG. 2 and Table 3. In the soil column, the total NAPL removed
(measured by total petroleum hydrocarbon, TPH, or gasoline range
organics, GRO) was 99.6%. Without the polishing step (chemical
oxidation), the surfactant flushing alone could not achieve
remediation to an extremely low contaminant level in the soil.
Direct injection of a high concentration Fenton's Reagent
(H.sub.2O.sub.2 level at 10 wt %) would have required multiple pore
volumes (>5 PV) to achieve 80% to 90% contaminant removal (data
not shown). Therefore, laboratory experiments indicated that
integrated surfactant flushing followed by chemical oxidation would
be able to treat the Golden site NAPL to extreme low level
concentrations (low ppb range).
[0046] In situ surfactant flushing was used to recover free phase
LNAPL (gasoline) using the low concentration surfactant (<1 wt
%) and polishing oxidant methodology of the presently disclosed and
claimed invention. One pore volume of 0.94 wt % AOT-Galfax16L-35
(Table IA) surfactant (190,000 gallons) was injected into the
contaminated shallow zone (source area, mostly silty material) over
a two month period to mobilize the trapped NAPL. Initial free phase
gasoline thickness on the water table ranged between 2.7 feet to
3.3 feet. Representative results from the field remediation effort
at the Golden UST site are shown in FIGS. 3 and 4 and in Tables 4
and 5.
5TABLE 4 Representative Contaminant Concentration in Golden Soil
before and after the Sequent Surfactant Flushing and Chemical
Oxidation Soil Sample Comparison Data Pre-Flush vs. Post Flush
Calfax/AOT Flush Percent Percent Sample Depth Benzene Toluene
Ethylbenzene Xylenes TPH-Gro Reduction Reduction Number ft. bgl.
ug/kg ug/kg ug/kg Ug/kg mg/kg Benzene TPH-Gro MLS-1A 12.5 13400.0
58100.0 18800.0 92700.0 809.0 PTGP-2A 12.5 511.0 9970.0 3520.0
20600.0 164.0 96.2 79.7 MLS-1B 14.0 16000.0 185000.0 85300.0
454000.0 3630.0 PTGP-2B 14.0 2350.0 37300.0 14600.0 78600.0 548.0
85.3 84.9 MLS-2A 12.5 31800.0 438000.0 114000.0 595000.0 5080.0
GP-7A 12.5 2400.0 41800.0 17100.0 95700.0 691.0 PTGP-9A 12.5 225.0
476.0 ND ND 56.0 99.3 98.9 MLS-2B 14.0 4980.0 26700.0 6640.0
38100.0 345.0 PTGP-9B 14.0 284.0 ND 527.0 3790.0 59.0 94.3 82.9
DW-1A 11.0 1900.0 14900.0 8750.0 48400.0 355.0 PTGP-1A 11.0 ND ND
ND ND 4.2 >99 98.8 DW-1B 14.0 11200.0 99800.0 44900.0 250000.0
2190.0 PTGP-1B 14.0 2670.0 4920.0 7580.0 28400.0 137.0 76.2 93.7
DW-5A.sup.1 14.0 20800.0 148000.0 58800.0 326000.0 2780.0 GP-6B
14.0 1210.0 12720.0 5820.0 31900.0 325.0 94.2 88.3 DW-8A 14.0
41100.0 182000.0 54600.0 277000.0 2560.0 PTGP-10A 14.0 1060.0
42700.0 19700.0 104000.0 890.0 97.4 65.2 DW-16A.sup.1 11.0 9720.0
277000.0 129000.0 707000.0 5740.0 PTGP-12A 11.0 ND 118.0 ND ND 19.0
>99 99.7 Notes: Background Concentration .sup.1The 14 foot
sample for DW-5A and DW-16A denotes the 14 foot depth, unlike
DW-1A.
[0047]
6TABLE 5 Oklahoma Corporation Commission (OCC)/U.S. Environmental
Protection Agency (U.S. EPA) Post Test Soil Sample Results Sample
Depth Concentration, mg/kg I.D. Ft. bgl. benzene Toluene
ethylbenzene xylenes TPH-Gro PB-1 15.8 0.425 1.93 1.12 4.29 88.3
PB-2 16.7 0.103 0.170 0.035 0.190 1.83 PB-2 18.5 2.27 8.07 2.390
13.4 111.0 PB-3 17.7 0.295 3.02 1.20 6.87 54.5 PB-3 18.5 0.165
0.374 0.054 0.299 2.40 PB-4 17.0 4.24 16.7 4.14 21.6 155 PB-5 10.2
0.072 0.675 0.28 1.86 18.8 PB-5 17.3 0.727 6.31 2.18 13.1 160.0
[0048] No visible or instrumental evidence of free phase gasoline
was detected in 25 recovery and monitoring wells (three out of 28
wells had minimal thicknesses) during the post surfactant sampling
event (FIG. 3). The observed benzene concentration indicated that
75%-99% reduction in soil concentrations were achieved during the
surfactant flush (FIG. 4 and Table 4). Similarly, a reduction of
TPH (GRO) concentrations in the soils was between 65%-99%. After
surfactant flushing, the remaining trace residual and dissolved
NAPL were treated by the final polishing steps using chemical
oxidation in the shallow zone, where most NAPL was present before
the surfactant flushing. Representative soil concentrations after
the post-oxidation phase are summarized in Table 5. As shown in
Tables 4 and 5, further contaminant reduction/degradation (OCC/EPA
soil sampling event held in June, 2002) was observed after the
post-polishing step was completed. These results indicate that the
integrated surfactant flushing and chemical oxidation methodology
of the presently disclosed and claimed invention is capable of
remediating contaminants to substantially non-detected or extremely
low level, if not completely removed, in a "real world" field-scale
test.
EXAMPLE 2
Sequent Surfactant Flushing and Chemical Oxidation Polishing for
DNAPL--a TCE-Contaminated Site
[0049] The targeted site was contaminated by TCE, a DNAPL and
common degreaser. The main focus of this experiment was to treat
the dilute TCE plume with an in-situ chemical oxidation process.
This approach was selected rather than treating the source zone
NAPL because the DNAPL source zones could not be identified. Most
laboratory efforts were focused on evaluating the effectiveness of
two selected oxidants, potassium permanganate (KMnO.sub.4) and
Fenton's reagent, for TCE and cis-DCE degradation. A limited effort
was given to evaluate the effectiveness of sequent surfactant
flushing and chemical oxidation to treat the TCE-contaminated
source (or hot) zone.
[0050] Use of Potassium Permanganate for TCE/DCE Degradation
[0051] Batch experiments were conducted to evaluate the degradation
rates of TCE, cis-DCE, or their mixture by KMnO.sub.4. These
experiments were carried out in TCE/DCE dissolved solutions in the
absence (Table 6) or presence (Table 7) of site-specific soil. As
shown in Table 6, 250 mg/L KMnO.sub.4 can degrade TCE or DCE
completely at low contaminant levels. Initial contaminant
concentrations ranged from several hundred of ug/L to more than 100
mg/L. As shown in Table 7, KMnO.sub.4 concentrations ranging from
10 mg/L up to 10,000 mg/L (1%) solution were tested. Results
indicated that most reactions between KMnO.sub.4 and TCE, DCE, and
TCE/DCE mixtures (between few hundreds ppb to 5 ppm) were complete
after a 24-hr reaction period.
7TABLE 6 Degradation Reaction of KMnO.sub.4 and low level of TCE,
DCE and their mixtures without soil KMnO4 TCE, DCE Final Final
added, % % Sample ID TCE ug/L DCE ug/L mg/L degraded degraded
DCE-C-8 8 4820 0 NA 0 (control) DCE-100-8 3 691 100 NA 85.7
DCE-250-8 0 22 250 NA 99.5 TCE-C-8 283 0 0 0 NA (control) TCE-100-8
0 1 100 100 NA TCE-250-8 0 1 250 100 NA D&T-C-8 70 1407 0 0 0
(control) D&T-100-8 0 14 100 100 99.0 D&T-250-8 0 11 250
100 99.2 Note: 8 samples were analyzed after 29 hrs of sample
preparation.
[0052]
8TABLE 7 Degradation Reaction of KMnO.sub.4 and TCE, DCE and their
mixtures with two types of soil (Soil 1-26'-27'; Soil 2-18'-20', in
40 mL solution) KMnO.sub.4 TCE DCE Final Final added % % Sample TCE
ug/L DCE ug/L mg/L degraded degraded SDCE-C 18 5486 0 NA 0 SDCE-100
0 17 100 NA 99.7 SDCE-250 0 16 250 NA 99.7 STCE-C 237 0 0 0 NA
STCE-100 0 0 100 100 NA STCE-250 0 0 250 100 NA ST&D-C 117 2432
0 0 0 ST&D-100 0 13 100 100 99.5 ST&D-250 0 12 250 100
99.5
[0053] Most reactions between KMnO.sub.4 and TCE/DCE are completed
in less than one hour under room temperature (20.degree. C.). As
shown in Table 8, experiments conducted with soil added indicate
that complete degradation of TCE and DCE was observed under similar
conditions.
9TABLE 8 Degradation Reaction of KMnO.sub.4 and high level of TCE
without soil Final TCE Initial KMnO.sub.4 TCE Sample ID mg/L added
mg/L % degraded Control 343 0.0 0 T10000 0.0 10,000 100 T5000 0.0
5,000 100 T1000 0.0 1,000 100 T500 111 500 67.7
[0054] The loss of KMnO.sub.4 in two soil samples collected from
the site were determined to be negligible during 4-, 7-, and
14-days of reaction period (data not shown). Low sorption loss of
KMnO.sub.4 reduced the amount of KMnO.sub.4 required and the total
cost of remediation project.
[0055] Under higher initial TCE levels (>300 mg/L), results
indicate that adding 1,000 mg/L or more KMnO.sub.4 completely
degraded the added TCE. A 67.7% reduction of TCE was observed with
500 mg/L of KMnO.sub.4 solution.
[0056] Batch study indicated that addition of potassium
permanganate degraded dissolved TCE and DCE in the dilute plume
near the vicinity of the soil sampling locations. In addition,
other loss mechanisms for permanganate including sorption and
fortuitous reactions with other reduced compounds were minimal in
the tested samples.
[0057] Use of Fenton's Reagent for TCE/DCE Degradation
[0058] Fenton's reagent is the second oxidant tested. Fenton's
reagent was prepared by dissolving H.sub.2O.sub.2 and catalysis
Fe(II) (FeCl.sub.2 or FeSO.sub.4) in acidic solution (HCl or
H.sub.2SO.sub.4).
[0059] Batch results indicated that Fenton's reagent degrades both
TCE and DCE, but appears less efficient compared to KMnO.sub.4 on a
weight basis. For example, 283 ug/L TCE can be completely degraded
by 100 mg/L KMnO.sub.4 solution, yet 100 mg/L
H.sub.2O.sub.2/FeCl.sub.2 solution only oxidize 51.7% of TCE. For
similar contaminant concentrations, DCE degradation required more
Fenton's reagent than TCE. Note that some pollutants, such as
trichloroethane (TCA) or BTEX, could not be completely degraded by
KMnO4, but will be degraded effectively by Fenton's reagent.
[0060] The batch studies clearly indicate that both KMnO.sub.4 and
Fenton's reagent were candidates for degrading the target
contaminant, TCE, and the common intermediate, DCE, at the selected
sampling locations at the DNAPL-impacted site.
[0061] 1-D Column Study with KMnO.sub.4-only for TCE Removal
[0062] Several column tests were conducted by injecting KMnO.sub.4
at different concentrations (100, 500, 5000, 20000 mg/L) under
various TCE residual saturation in the soil packed column. In the
column study, fifteen to twenty five pore volumes of KMnO.sub.4
were injected to evaluate the removal of TCE under the hydrodynamic
conditions.
[0063] At a 1% initial TCE residual saturation, significant gas
bubbles (mainly CO.sub.2 gas) were observed in the effluent after a
5,000-mg/L KMnO.sub.4 solution was injected, while TCE
concentration also began to drop significantly (to less than 10
mg/L level). In another column test, a 10% TCE residual saturation
was used with various KMnO.sub.4 levels being injected (100, 500,
5,000, 20,000 mg/L). Similarly, numerous gas bubbles were created
when higher KMnO.sub.4 concentrations were injected (5,000 mg/L and
above) (data not shown). In addition, dark brown MnO.sub.2
precipitates were accumulated at various locations in the
column.
[0064] After the KMnO.sub.4 flushing, the treated column was
dismantled and the soil was extracted with methanol to determine
the final TCE concentration. The final TCE concentrations in the
column ranged from 8 mg/Kg to 47 mg/Kg in different columns (both
low and high initial TCE levels). A significant amount of TCE was
degraded with KMnO.sub.4 flushing. However, a significant release
of CO.sub.2 near the NAPL source area could potentially change the
hydraulic permeability of the aquifer and lead to by-pass around
the TCE ganglia preventing further removal, as other researchers
have suggested. In addition, significant accumulation of MnO.sub.2
precipitates at the interface of NAPL and water also reduce the
mass transfer of KMnO.sub.4 to TCE and decrease the TCE degradation
rate. This problem has been observed in field trials with
KMnO.sub.4 and is a limitation of the technology for remediation of
contaminated hot zone. Results from these column tests indicate
that injection of KMnO.sub.4 alone could effectively degrade TCE
under proper conditions, such as for a TCE-impacted dissolved plume
but not in areas with free phase DNAPL or high level of TCE
residual saturation. Chemical oxidation is very effective for
degrading a TCE dilute plume or as a polishing-step for source zone
remediation after the majority of the TCE is removed by the
surfactant flooding. The relatively low quantity of remaining TCE
would be less likely to cause manganese precipitation and hydraulic
bypassing upon reaction with KMnO.sub.4.
[0065] 1-D Column Study with Sequent Surfactant Flushing and
Chemical Oxidation (KMnO.sub.4) Flushing for TCE Removal
[0066] Additional column tests were conducted using surfactant
flushing to first remove significant TCE NAPL mass, followed by
KMnO.sub.4 flushing to degrade the TCE left in the column. Examples
of the column study results are shown in FIG. 5. Initial TCE
residual saturation was 2%. At 4 PV, a surfactant solution,
containing 2.5% dihexyl sulfosuccinate (AMA), 5% diphenyl oxide
disulfonate (Calfax), 3% NaCl, and 1% CaCl.sub.2, was injected into
the column. The selection of this surfactant system was based on a
previous field test done for a mixed DNAPL contaminated site,
containing tricholorethane (TCA), TCE, DCA, and DEC. The
enhancement of TCA solubility with the selected surfactant system
(Calfax/AMA/CaCl.sub.2/NaCl) is listed in Table 9.
10TABLE 9 Comparison of Trichloroethane (TCA) Solubilization in
Batch and Column Studies TCA Solubilized Maximum TCA in Batch test
Solubilized in Surfactant System (mg/L).sup.1 column test (mg/L)
Dowfax/AMA/NaCl/CaCl.sub.2 99,259 168,996
Lubrizol71/IPA/NaCl/CaCl.sub.2 259,355 NA.sup.3 .sup.1Volume
determined by volumetric addition of TCA during the phase behavior
study .sup.2Surfactant used in the sequent surfactant
flushing/chemical oxidation test .sup.3NA = not available
[0067] A surfactant system used for TCA could be used for TCE (with
similar hydrophobicity property) to produce a middle-phase
microemulsion. Therefore, a mixture of Calfax/AMA surfactant was
used to conduct this 1-D column test. Significant TCE mass
(concentration reached 100,000 mg/L) was removed from the column
after surfactant breakthrough. After 5 PV of surfactant flushing, a
2,000 mg/L KMnO.sub.4 solution was injected to further degrade the
TCE in the column. A total of 4 PV of KMnO.sub.4 solution was
injected in the column before post-water flushing began at 12 PV
injection time.
[0068] Significant TCE mass was removed during the surfactant
flushing period. A decrease of the TCE concentration, eventually
below the quantification limit, after the KMnO.sub.4 breakthrough,
is also clearly demonstrated. Post column extraction indicated that
99.94% of the initial TCE was removed from the column. Note that
the surfactant concentration used in this column test was 7.5 wt %.
As shown in Table 10, a recent batch study conducted by Applicant
indicates that a low surfactant concentration (<1 wt %) could
achieve similar solubility enhancement for TCE.
11TABLE 10 Solubilozation of DNAPL (TCE) Using Low Surfactant
Concentration (1 wt %) Sample TCE Solubilized Note Name Phase in
bacth test mg/L 1 wt % surfactant fb-015s middle 177104 Calfax/AOT
fb-015s aqueous 99577 Calfax/AOT fb-014s middle 383813 Calfax/AOT
fb-014s aqueous 66677 Calfax/AOT fb-008 aqueous 152882 Lubrizol
System
[0069] Therefore, a surfactant flushing with a low surfactant
concentration system (e.g., Calfax/AOT--see Table IA for TCE)
followed by a chemical oxidation step significantly improves the
state of the art and makes it technologically and economically
viable to completely remediate contaminated sites.
[0070] Although the present invention has been described in
considerable detail with reference to certain preferred versions
thereof, other versions are possible. For example, single
surfactant systems such as anionic/anionic and nonionic/nonionic
mixtures; surfactant systems such as anionic/cationic and
anionic/nonionic mixtures; and contaminants such as polyaromatic
hydrocarbons (PAH), creosote, crude oil, pesticides, polychorinated
biphenyls (PCBS) and ketones can be utilized with this integrated
approach. Therefore, the spirit and scope of the appended claims
should not be limited to the description of the preferred versions
contained herein.
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