Engineered in situ anaerobic reactive zones

• US 6,322,700 B1
• Filed: 08/02/2000
• Issued: 11/27/2001
• Est. Priority Date: 04/11/1995
• Status: Expired due to Term

• Current Assignee: Arcadis US Incorporated (Arcadis N.V.)
• Original Assignee: Arcadis Geraghty & Miller Inc. (Arcadis N.V.)
• Inventors: Suthersan, Suthan S.
• Primary Examiner(s): Upton, Christopher
• Application Number:
  US09/630,790
• Time in Patent Office: 482 Days
• Field of Search: 210/603, 210/610, 210/611, 210/747, 210/605, 210/903, 210/908, 210/912, 210/913, 210/614, 210/717, 435/262.5
• US Class Current: 210/610
• CPC Class Codes: B09C 1/002 involving in-situ ground water treatment
• CPC Class Codes: B09C 1/10 microbiologically, biologically or by using enzymes
• CPC Class Codes: B09C 2101/00 In situ
• CPC Class Codes: C02F 2101/20 Heavy metals or heavy metal compounds
• CPC Class Codes: C02F 2101/322 Volatile compounds, e.g. benzene
• CPC Class Codes: C02F 2101/36 containing halogen
• CPC Class Codes: C02F 3/306 Denitrification of water in soil
• CPC Class Codes: Y10S 210/903 Nitrogenous
• CPC Class Codes: Y10S 210/908 Organic
• CPC Class Codes: Y10S 210/912 Heavy metal
• CPC Class Codes: Y10S 210/913 Chromium

Abstract

An in situ method and system for reductive dechlorination, the precipitation of chromium, the precipitation of heavy metals, and microbial denitrification. The invention comprises the formation of in situ anaerobic reactive zones to precipitate and filter out dissolved heavy metals as metallic sulfides, to degrade nitrate to nitrogen gas, to reduce chlorinated hydrocarbons to ethene, and to precipitate and filter out chromium. The invention is comprised of an injection well or wells that extend into a contaminated groundwater. A conduit located within the injection well conveys carbohydrates and sulfates to the contaminated groundwater. Microbes digest the carbohydrates to produce sulfate reducing and methanogenic conditions within the reactive zone that include a dissolved oxygen level less than about 0.5 mg/l, a redox potential less than about −250 mv, and a dissolved organic carbon to contaminant ratio of greater than about 50:1. These biogeochemical conditions lead to the reduction of PCE to TCE to DCE to VC and eventually to ethene. These biogeochemical conditions also lead to the precipitation of heavy metals, the precipitation of chromium, and microbial denitrification.

Claims

1. A method for removing contaminants dissolved in groundwater, said method comprising the steps of:

supplying carbohydrates and sulfates to contaminated groundwater;

wherein microorganisms in the contaminated groundwater metabolize said carbohydrates creating an anaerobic condition which leads to the precipitation of trivalent chromium as chromic hydroxide.

2. The method of claim 1 further comprising:

providing at least one injection well extending from the ground surface to the contaminated groundwater; and

placing a conduit within said at least one injection well, said conduit having a fluid-permeable section below the water table of the contaminated groundwater;

wherein said carbohydrates and sulfates are forced out of said fluid-permeable section into the contaminated groundwater.

3. The method of claim 1 wherein said anaerobic condition comprises:

a dissolved oxygen level less than about 0.5 mg/l;

a redox potential less than about −

250 mv; and

a dissolved organic carbon to contaminant ratio of greater than about 50;

1.

4. A method for removing contaminants dissolved in groundwater, said method comprising the steps of:

supplying carbohydrates and sulfates to contaminated groundwater;

wherein microorganisms in the contaminated groundwater metabolize said carbohydrates creating an anaerobic condition which leads to the precipitation of metal compounds.

5. The method of claim 4 further comprising:

providing at least one injection well extending from the ground surface to the contaminated groundwater; and

placing a conduit within said at least one injection well, said conduit having a fluid-permeable section below the water table of the contaminated groundwater;

wherein said carbohydrates and sulfates are forced out of said fluid-permeable section into the contaminated groundwater.

6. The method of claim 4 wherein said anaerobic condition comprises:

a dissolved oxygen level less than about 0.5 mg/l;

a redox potential less than about −

250 mv; and

a dissolved organic carbon to contaminant ratio of greater than about 50;

1.

7. A method for removing contaminants dissolved in groundwater, said method comprising the steps of:

supplying carbohydrates and sulfates to contaminated groundwater;

wherein microorganisms in the contaminated groundwater are catalysts for the creation of an anaerobic condition which leads to the precipitation of trivalent chromium as chromic hydroxide.

8. The method of claim 7 further comprising:

providing at least one injection well extending from the ground surface to the contaminated groundwater; and

placing a conduit within said at least one injection well, said conduit having a fluid-permeable section below the water table of the contaminated groundwater;

wherein said carbohydrates and sulfates are forced out of said fluid-permeable section into the contaminated groundwater.

9. The method of claim 7 wherein said anaerobic condition comprises:

a dissolved oxygen level less than about 0.5 mg/l;

a redox potential less than about −

250 mv; and

a dissolved organic carbon to contaminant ratio of greater than about 50;

1.

10. A method for removing contaminants dissolved in groundwater, said method comprising the steps of:

supplying carbohydrates and sulfates to contaminated groundwater;

wherein microorganisms in the contaminated groundwater are catalysts for the creation of an anaerobic condition which leads to the precipitation of metal compounds.

11. The method of claim 10 further comprising:

providing at least one injection well extending from the ground surface to the contaminated groundwater; and

placing a conduit within said at least one injection well, said conduit having a fluid-permeable section below the water table of the contaminated groundwater;

wherein said carbohydrates and sulfates are forced out of said fluid-permeable section into the contaminated groundwater.

12. The method of claim 10 wherein said anaerobic condition comprises:

a dissolved oxygen level less than about 0.5 mg/l;

a redox potential less than about −

250 mv; and

a dissolved organic carbon to contaminant ratio of greater than about 50;

1.

13. A method for removing contaminants dissolved in groundwater, said method comprising the steps of:

supplying carbohydrates and sulfates to contaminated groundwater;

wherein microorganisms in the contaminated groundwater are adapted to metabolize said carbohydrates and said sulfates to produce sulfide ions, thereby serving as catalysts for the precipitation of trivalent chromium as chromic hydroxide.

14. The method of claim 13 further comprising:

providing at least one injection well extending from the ground surface to the contaminated groundwater; and

placing a conduit within said at least one injection well, said conduit having a fluid-permeable section below the water table of the contaminated groundwater;

wherein said carbohydrates and sulfates are forced out of said fluid-permeable section into the contaminated groundwater.

15. A method for removing contaminants dissolved in groundwater, said method comprising the steps of:

supplying carbohydrates and sulfates to contaminated groundwater;

wherein microorganisms in the contaminated groundwater are adapted to metabolize said carbohydrates and said sulfates to produce sulfide ions, thereby serving as catalysts for the precipitation of metal compounds.

16. The method of claim 15 further comprising:

providing at least one injection well extending from the ground surface to the contaminated groundwater; and

placing a conduit within said at least one injection well, said conduit having a fluid-permeable section below the water table of the contaminated groundwater;

wherein said carbohydrates and sulfates are forced out of said fluid-permeable section into the contaminated groundwater.