WO1999042182A1

WO1999042182A1 - Method and apparatus for removing chlorinated contaminants from soil

Info

Publication number: WO1999042182A1
Application number: PCT/US1998/003050
Authority: WO
Inventors: Richard P. Murray
Original assignee: Murray Richard P
Priority date: 1998-02-19
Filing date: 1998-02-19
Publication date: 1999-08-26
Also published as: AU6328998A

Abstract

A soil remediation system (20) includes a reagent mixer (32) for producing a metal suspension reagent (31) containing zero-valent iron. A pump (36) propels the metal suspension reagent (31) from the reagent mixer (32) to a hollow shaft (26) for subsequent ejection from an ejection nozzle (50). A drill assembly (24) is coupled to the hollow shaft (26) and blends the metal suspension reagent (31) into the soil (22) to form a homogeneous mixture. The oxidation of the zero-valent iron in the metal suspension reagent (31) causes a reductive dechlorination effect in the soil (22) to reduce the chlorinated contaminants to less hazardous end-products.

Description

-1-

METHOD AND APPARATUS FOR REMOVING CHLORINATED CONTAMINANTS FROM SOIL

TECHNICAL FIELD This invention relates in general to soil remediation, and in particular, to a system and method for the removal of chlorinated contaminants from soil.

BACKGROUND ART

Polychlorinated hydrocarbons, such as carbon tetrachloride, chloroform, trichloroethylene, and tetrachloroethylene have been widely used as chemical intermediates, solvents for dry cleaning of clothing, in degreasing operations, and in a variety of other applications. Chlorinated hydrocarbons are very stable compounds .and are relatively toxic at low levels. In some regions, the soil has become contaminated by these chlorinated hydrocarbons from sources such as disposal facilities, chemical spills, leaking storage tanks, and so forth.

The accumulation of chlorinated hydrocarbons in the soil poses a hazardous soil contamination problem. Moreover, the chlorinated hydrocarbons in the soil can be carried into groundwater sources by water percolating through the soil thus contaminating the groundwater. As a result, pollution of soil and the subsequent pollution of groundwater by chlorinated hydrocarbons has become an important environmental concern that has stimulated the development of remediation, or treatment, systems for contaminated soils.

One conventional soil remediation method is a physical process to remove and alter hazardous waste material from ground sites. In this method, the contaminated soil is permanently removed from the site. Alternatively, the soil is removed, chemically treated to remove chlorinated contaminants, and replaced. These methods may be effective for shallow regions of contaminated soil, for example, less than five feet. However, they .are cost prohibitive in areas where the soil contamination is deep. Furthermore, the chlorinated contaminants are intact in the soil that is merely removed from the contaminated site and are still hazardous. -2-

Another soil remediation method involves drilling and in-situ, or in place, soil mixing and treatment. Mixing is performed by earth augers, or drills. One treatment method calls for treating the soil with hot air and steam. The hot air and steam results in driving off some of the chlorinated contaminants from the soil in the off gas stream. Unfortunately, .an unacceptably high level of chlorinated contaminants still remain in the soil. In addition, the chlorinated contaminants are not effectively destroyed, but rather, they are discharged into the atmosphere which results in contamination of the atmosphere.

Granular activated carbon has been used to adsorb the vapor phase chlorinated contam.in.ants from the off gas stream in order to prevent their release into the atmosphere. However, this poses -another cleanup problem since the activated carbon must periodically be flushed or otherwise treated to remove or drive off the chlorinated contaminants that have accumulated. The chlorinated contaminants from the activated carbon are still intact and still hazardous. Moreover, the contaminants are even more hazardous because they are concentrated.

It is known that chlorinated compounds can be degraded by reductive dechlorination, that is, replacement of chlorine substituents by hydrogen. Metallic elements, such as iron and zinc, have been used to degrade chlorinated organic compounds in aqueous solutions, such as groundwater. One such process involves feeding contaminated groundwater through a wall containing a metal such as zero-valent iron. As the contaminated water enters the wall, reactions occur that either transform the cont.amin.ant into a less hazardous chemical substance or immobilize the contaminant permanently in the wall. Water exiting the downgradient side of the wall is thus freed of the initial contaminant. Unfortunately, this process is not applicable to soil remediation since soil does not have the flow characteristics of water and is not be able to permeate the iron filled wall. DISCLOSURE OF INVENTION

Accordingly, it is an advantage of the present invention that a soil remediation system and method are provided for the removal of chlorinated contaminants.

Another advantage of the present invention is that a soil remediation system and method effectively degrades chlorinated contaminants into less hazardous chemical substances.

Another advantage of the present invention is that a soil remediation system and method are provided for cost effective removal of chlorinated contaminants.

The above and other advantages of the present invention are carried out in one form by a soil remediation system for removing chlorinated contaminants from soil. The system includes a reagent mixer for producing a metal suspension reagent. A means for delivery of the metal suspension reagent to the soil is coupled to the reagent mixer. A means for blending the metal suspension reagent into the soil is coupled to the delivery means. The metal suspension reagent causes a reductive dechlorination effect in the soil to remove the chlorinated contaminants.

The above and other advantages of the present invention are carried out in another form by a soil remediation method for removing chlorinated contaminants from soil.

The method calls for blending a reagent containing particles of metal into the soil. The method further calls for reducing the chlorinated contaminants through an oxidation of the metal to remove the chlorinated contaminants.

BRIEF DESCRIPTION OF DRAWINGS

A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, wherein like reference numbers refer to similar items throughout the Figures, .and:

FIG. 1 shows a soil remediation system for the removal of chlorinated contaminants from soil;

FIG. 2 shows a drill assembly and ejection nozzle of the soil remediation system; and FIG. 3 shows the soil remediation system with a hood and filter for capturing vapors of the chlorinated contaminants.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows a soil remediation system 20 for the removal of chlorinated contaminants from soil 22. A drill assembly, such as an auger 24, is coupled to and rotates on a hollow shaft 26 about an axis 28. Auger 24 bores into and loosens soil 22 in a columns pattern through a predetermined soil depth 30. Predetermined soil depth 30 is the depth of soil 22 through which chlorinated contaminants are present. In addition, auger 24 blends a metal suspension reagent 31 into soil 22 through predetermined soil depth 30. In some cases a dual auger arrangement (not shown) is utilized for more thorough loosening and blending of soil 22.

System 20 includes a reagent mixer 32 which is in fluid communication with hollow shaft 26 by a hose 34. Reagent mixer 32 produces metal suspension reagent 31 which is then propelled by a pump 36 through hose 34 to hollow shaft 26 for subsequent delivery to soil 22. Alternatively, metal suspension reagent 31 may be pumped to an intermediate holding tank (not shown) until needed.

Metal suspension reagent 31 is a composition of water, a metal, and a suspension agent in a pumpable liquid/slurry state. Metal suspension reagent 31 is produced in reagent mixer 32 by utilizing a suspension agent such as G150 Biopolymer produced by Rantec Corporation, Ranchester, WY 82839. G150 Biopolymer has been used extensively for geo-technical stabilization of extraction trenches during excavation and construction, and well bores during drilling. G150 Biopolymer is a natural organic polymer often used in food ingredients as well as industrial applications, and is non- polluting, non-toxic, and biodegradable.

G150 Biopolymer is mixed with water to produce a viscous solution thick enough to suspend the metal. After reagent mixer 32 has mixed G150 Biopolymer with water to a viscous state, the metal is added to the mixture.

The metal used in metal suspension reagent 31 is a zero-valent iron in the form of either iron filings or a concentrated liquid. One such product is Iron Aggregate produced -5-

by Connelly-GPM, Inc., Chicago, IL 60609. Reagent mixer 32 mixes the zero-valent iron into the G150 Biopolymer/water mixture until the zero-valent iron is evenly distributed throughout the mixture, thus creating a homogeneous slurry of metal suspension reagent 31. The amount of zero-valent iron to be mixed into the G150 Biopolymer/water mixture is variable and is determined by the types and concentration of the chlorinated contaminants in soil 22, as well as the physical properties of soil 22 (FIG. 1). In general, the amount of zero-valent iron in metal suspension reagent 31 is in a range of one to five percent of the weight of soil 22 being treated. This equates to between thirty .and one hundred and fifty pounds of zero-valent iron per cubic yard of soil treated.

A controller 38 is in communication with pump 36. Controller 38 includes sensors (not shown) that monitor and control the mix-proportion of metal suspension agent 31 and soil 22. In addition, controller 38 monitors and controls the volume and injection pressures of metal suspension reagent. Controller 38 sustains strict quality control of the expended metal suspension agent 31, thus assuring that the correct ratio of metal suspension agent 31 and soil 22 is maintained.

FIG. 2 shows the drill assembly, auger 24, connected to hollow shaft 26. Auger 24 includes a nose flight 40 located at the bottom edge of auger 24 when boring in a vertical direction. A plurality of fin cutters 42 reside on nose flight 40. Fin cutters 42 are attached, for example, by being welded to nose flight 40. Fin cutters 42 .are designed to make the primary or first cut during the boring operation to score soil 22 (FIG. 1) in a substantially parallel direction to axis 28, to complete a vertical cut.

Auger 24 additionally has scraping blades 44. Scraping blades 44 cut in a substantially perpendicular direction to axis 28 to make a generally horizontal circular cut as auger 24 bores vertically into soil 22. Scraping blades 44 work in cooperation with fin cutters 42 to break soil 22 into chunks which are then passed up to a plurality of flights 46 for mixing.

Flights 46 are positioned on hollow shaft 26. Flights 46 contain a plurality of mixing holes 48. Mixing holes 48 extend through flights 46 in a direction substantially parallel to axis 28. Mixing holes 48 are of a size to allow for the passing and mixing of -6-

chunks of soil 22. In addition, mixing holes 48 have an arrangement that permits them to be axially unaligned. This unalignment contributes to the mixing process. It creates a churning movement as the chunks search for the next mixing hole 48 to past through. An ejection nozzle 50 is coupled to hollow shaft 26 proximate flights 46 of auger 24. Hollow shaft 26 is configured to convey metal suspension agent 31 (FIG. 1) from hose 34 (FIG. 1) to ejection nozzle 50 to be ejected by ejection nozzle 50. As chunks of soil 22 are churned and mixed by the rotation of auger 24, metal suspension agent 31 is injected into and blended with soil 22. The configuration of auger 24 causes metal suspension reagent 31 to be blended into soil 22 to form a substantially homogeneous mixture of metal suspension reagent 31 and soil 22 throughout predetermined soil depth 30. In some cases, a plurality of ejection nozzles 50 may be utilized for more thorough disbursement of metal suspension reagent 31 into soil 22.

The corrosion (oxidation) of zero-valent iron in metal suspension reagent 31 produces a reducing chemical state and strong electro-negativity potential in soil 22. Under this condition, hydrogen replaces chlorine in the chlorinated contaminants causing reductive dechlorination of the polychlorinated hydrocarbons, such as the carbon tetrachloride, chloroform, trichloroethylene, tetrachloroethylene, or other such substances which may be present in soil 22. The end-products of the process are dechlorinated and non-toxic. Examples of end-products for reduced chlorinated hydrocarbons include, but are not limited to, ethane, ethene, methane, propane, butane, pentane, and chloride ions.

FIG. 3 shows soil remediation system 20 with a hood 52 and filter 54 for capturing vapors of the chlorinated contaminants. Hood 52 is coupled to hollow shaft 26 and auger 24 and fits tightly on the soil 22 surrounding auger 24. Hood 52 is configured to capture vapors of the chlorinated contaminants and send the captured vapors to a surface treatment system such as filter 54.

The chlorinated contaminants are volatile organic compounds which volatilize, or vaporize, readily. If during the soil loosening and blending process the chlorinated contaminants or their end-products become airborne, hood 52 captures the airborne products and directs them to filter 54. Filter 54 may be granular activated carbon, a scrubber, a catalytic oxidizer, or some other system that is configured to substantially prevent the chlorinated contaminants or their end-products from escaping into the atmosphere.

A soil remediation method for removing chlorinated contaminants utilizing system 20 includes blending metal suspension reagent 31 into soil 22 (FIG. 1) while auger 24 (FIG. 1) is rotating. The blending action of auger 24 results in a homogeneous mixture of soil 22 and metal suspension reagent 31. To enhance the effectiveness of the reductive dechlorination, hollow shaft 26 is further configured to deliver hot air and high pressure steam to soil 22. The hot air and high pressure steam may be delivered to hollow shaft 26 through hose 34 or through an alternate source (not shown).

The steam heats soil 22, thermally desorbing the chlorinated contaminants and also volatilizing the non-adsorbed free volatile organic compounds. The hot air carries the volatilized chlorinated contaminants to the surface of soil 22. The volatilized chlorinated contaminants are then captured by hood 52 and treated by filter 54. Hot air and high pressure steam treatment is useful for low permeability soils, such as clay and soils with layers of variable permeability. Soil 22 is first treated by injecting hot air and steam through ejection nozzle 50 into soil 22 as soil 22 is loosened and mixed. Following the hot air and steam treatment, auger 24 blends metal suspension reagent 31 into soil 22 as reagent 31 is ejected by ejection nozzle 50. By this process, the steam and air remove part of the chlorinated contaminants and the zero-valent iron in metal suspension reagent 31 removes the remaining chlorinated contaminants.

In an alternate embodiment, the hot air and steam may be injected into soil 22 substantially concurrent with the injection of metal suspension reagent 31. This single pass process eliminates the costs associated with the two pass approach and reduces the process length.

A process is described whereby chlorinated contaminants are removed by system 20 in-situ. In other words, soil 22 remains generally in place as it is being treated. This in-situ treatment is less costly than physical removal and treatment of soil 22. However, those skilled in the art will recognize that this soil remediation process may be adapted for sites where the depth of the contaminated soil is shallow. In such a case, the contaminated soil can be excavated then mixed with metal suspension reagent 31 in a pugmill, or other such mixing apparatus.

In summary, a soil remediation system and method are provided for the removal of chlorinated contaminants in by reductive dechlorination. A chemically reducing state is created in the soil by the blending of zero-valent iron into the soil. The oxidation of the zero-valent iron causes the chlorinated contaminants to undergo a chemical reduction to degrade the chlorinated contaminants into less hazardous chemical substances. The in-situ soil remediation method provides for cost effective removal of chlorinated contaminants. Although the preferred embodiments of the invention have been illustrated and described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims. For example, other metals having the appropriate valence characteristics may be used. In addition, other soil mixing systems may be utilized to produce a homogeneous mixture of soil and metal suspension reagent.

Claims

-9-CLAIMSWhat is claimed is:

1. A soil remediation system (20) for removing chlorinated contaminants from soil (22), said system (20) comprising: a reagent mixer (32) for producing a metal suspension reagent (31); means (22,50), in fluid communication with said reagent mixer (32), for delivery of said metal suspension reagent (31) to said soil (22); and means (24), coupled to said delivery means (22,50), for blending said metal suspension reagent (31) into said soil (22), said metal suspension reagent (31) causing a reductive dechlorination effect in said soil (22) to remove said chlorinated contaminants.

2. A soil remediation system (20) as claimed in claim 1 wherein said reagent mixer (32) is configured to produce said metal suspension reagent (31) consisting essentially of water, a metal, and a suspension agent.

3. A soil remediation system (20) as claimed in claim 2 wherein said metal is a zero-valent iron, an amount of said zero-valent iron in said metal suspension reagent (31) being in a range of one to five percent of the weight of said soil (22).

4. A soil remediation system (20) as claimed in claim 1 wherein said reagent mixer (32) further comprises a pump (36) configured to propel said metal suspension reagent (31) to said delivery means (26,50).

5. A soil remediation system (20) as claimed in claim 1 further comprising a controller (38) in communication with said delivery means (26,50) for monitoring a mix-proportion of said reagent (31) and said soil (22). -10-

6. A soil remediation system (20) as claimed in claim 1 wherein said delivery means (26,50) comprises: a hollow shaft (26) configured to convey said metal suspension reagent (31); and an ejection nozzle (50) coupled to said hollow shaft (26) for ejecting said metal suspension (31) into said soil (22).

7. A soil remediation system (20) as claimed in claim 6 wherein said blending means is a drill assembly (24), and said ejection nozzle (50) is located proximate said drill assembly (24).

8. A soil remediation system (20) as claimed in claim 7 wherein said drill assembly (24) is configured to blend said metal suspension reagent (31) into said soil (22) to a predetermined soil depth (30) to form a substantially homogeneous mixture of said metal suspension reagent (31) and said soil (22) throughout said predetermined soil depth (30).

9. A soil remediation system (20) as claimed in claim 1 wherein said delivery means (26,50) is further configured to deliver hot air and high pressure steam to said soil (22).

10. A soil remediation system (20) as claimed in claim 1 further comprising a hood (52) coupled to said blending means (24) for capturing vapors of said chlorinated contaminants.

11. A soil remediation system (20) as claimed in claim 10 further comprising a filter (54) coupled to said hood (52) for substantially preventing said chlorinated contaminants from escaping into the atmosphere. -11-

12. A soil remediation method for removing chlorinated contaminants from soil (22), said method comprising the steps of: blending (24) a reagent (31) into said soil (22), said reagent (31) containing particles of a metal; and reducing said chlorinated contaminants through an oxidation of said metal to remove said chlorinated contaminants.

13. A soil remediation method as claimed in claim 12 wherein said metal is zero-valent iron, and said method further comprises the step of mixing (32) an amount of said zero-valent iron with water and a suspension agent to produce said reagent (31), said amount of said zero-valent iron being in a range of one to five percent of the weight of said soil (22).

14. A soil remediation method as claimed in claim 12 wherein said blending step (24) comprises the step of controlling (38) a mix-proportion of said reagent (31) and said soil (22).

15. A soil remediation method as claimed in claim 12 wherein said blending step (24) comprises the step of disbursing said reagent (31) through a predetermined depth (30) of said soil (22), said predetermined depth (30) being a soil depth through which said chlorinated contaminants are present.

16. A soil remediation method as claimed in claim 15 wherein said blending step is performed by a drill assembly (24) to loosen said soil (22), and said blending step further comprises the step of ejecting said reagent (31) through a nozzle (50) located proximate said drill assembly (24) step to produce a substantially homogeneous mixture of said loosened soil (22) and said reagent (32). -12-

17. A soil remediation method as claimed in claim 12 wherein said blending step comprises the step of injecting (50) hot air, high pressure steam, and said reagent (31) into said soil.

18. A soil remediation method as claimed in claim 17 wherein said hot air and said high pressure steam are injected into said soil (22) prior to injecting said reagent (31).

19. A soil remediation method as claimed in claim 12 wherein said chlorinated contaminants are chlorinated volatile organic compounds and said method further comprises the step of capturing (52,54) vapors of said chlorinated volatile organic compounds.

20. A soil remediation system (20) for removing chlorinated contaminants from soil (22), said system (20) comprising: a reagent mixer-pump assembly (32,36) configured to produce a metal suspension reagent (31), said metal suspension reagent (31) consisting essentially of water, zero- valent iron, and a suspension agent; a hollow shaft (26), in fluid communication with said reagent mixer-pump assembly (32,36), and configured to convey said metal suspension reagent (31); an auger (24), coupled to said hollow shaft (26), for uniformly blending said metal suspension reagent (31) into said soil (22); and an ejection nozzle (50) coupled to said hollow shaft (26) in a location proximate said auger (24) for ejecting said metal suspension reagent (31) into said soil (22), said metal suspension reagent (31) producing a reductive dechlorination effect in said soil (22) to remove said chlorinated contaminants.