Engineered in situ anaerobic reactive zones

• US 6,632,364 B1
• Filed: 06/08/2001
• Issued: 10/14/2003
• Est. Priority Date: 04/11/1995
• Status: Expired due to Fees

• Current Assignee: Arcadis US Incorporated (Arcadis N.V.)
• Original Assignee: Arcadis G&M Incorporated (Arcadis N.V.)
• Inventors: Suthersan, Suthan S.
• Primary Examiner(s): Upton, Christopher
• Application Number:
  US09/877,948
• Time in Patent Office: 858 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, 435/262
• 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 a reagent to the contaminated groundwater.

The reagent may be a carbohydrate rich solution. 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 from groundwater, said method comprising the steps of:

supplying reagent to contaminated groundwater, whereby microorganisms in the contaminated groundwater metabolize said reagent creating an anaerobic condition sufficient to enable dechlorination of said contaminants; and

maintaining said anaerobic condition while promoting the continuous transformation of a chlorinated compound present in the contaminated groundwater into lesser chlorinated compounds, said transformation resulting in the reduction of said chlorinated compound to a non-chlorinated compound,

and wherein, under said anaerobic condition, microorganisms in said contaminated groundwater are catalysts for the precipitation of metal compounds.

2. The method of claim 1 wherein said anaerobic condition further leads to the precipitation of trivalent chromium as chromic hydroxide.

3. The method of claim 1 wherein said anaerobic condition further leads to microbial denitrification.

4. The method of claim 1 wherein microorganisms in the contaminated groundwater are catalysts of the reduction of VC to ethene.

5. The method of claim 1 wherein said chlorinated compound is selected from the group consisting of PCE, TCE, DCE, and VC.

6. The method of claim 1 wherein, under said anaerobic condition, microorganisms in the contaminated groundwater are catalysts of microbial denitrification.

7. The method of claim 1 wherein at least a portion of the microorganisms in the contaminated groundwater are supplied to the contaminated groundwater.

8. The method of claim 1 wherein the step of supplying said reagent comprises the step of supplying a carbohydrate rich solution.

9. The method of claim 1 wherein the reagent is selected from the group consisting of molasses extract, corn syrup, whey cheese, lactose, milk curd, cheese, fat, sugar, fruit juice, vegetable juice, dextrose, maltose, galactose, starch, fructose, sucrose, cornstarch, and vegetable oil.

10. 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.

11. The method of claim 1 wherein the step of supplying said reagent comprises:

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

placing a pump in fluid communication with said at least one injection well; and

operating said pump to force said reagent into the contaminated groundwater.

12. The method of claim 11 further comprising the step of mixing said reagent in said at least one injection well.

13. The method of claim 11 further comprising:

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 reagent is forcibly expelled from said fluid-permeable, thereby flowing outwardly from said at least one injection well with the natural flow of the contaminated groundwater and creating a three-dimensional reactive zone within the contaminated groundwater.