Insitu anaerobic reactive zone for insitu metals precipitation and to achieve microbial de-nitrification

• US 5,554,290 A
• Filed: 04/11/1995
• Issued: 09/10/1996
• Est. Priority Date: 04/11/1995
• Status: Expired due to Term

• Current Assignee: Piedmont Olsen Hensley, Inc. (Arcadis N.V.)
• Original Assignee: Geraghty & Miller, Inc. (Arcadis N.V.)
• Inventors: Suthersan, Suthan S.
• Primary Examiner(s): Upton, Christopher
• Application Number:
  US08/420,234
• Time in Patent Office: 518 Days
• Field of Search: 210/610, 210/611, 210/747, 210/901, 210/198, 210/1, 210/170, 210/903, 210/717, 210/912, 166/246, 166/312, 166/68, 405/128, 435/262, 435/262.5, 435/264
• 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 210/912 Heavy metal

Abstract

An insitu method and system for removing dissolved heavy metals and nitrates from groundwater is disclosed. The invention comprises the formation of insitu anaerobic reactive zones to precipitate and filter out dissolved heavy metals as metallic sulfides and to degrade nitrate to nitrogen gas. The invention is comprised of an injection well or wells into a saturated zone that contains dissolved heavy metals or nitrate contaminated groundwater. A conduit, located within the injection well, pumps carbohydrates in the case of nitrates, into the contaminated groundwater. Indigenous microbes digest the carbohydrates, producing an anaerobic condition within the reactive zones. In the presence of sulfates, the sulfates are reduced to sulfide ions. The sulfides readily combine with the dissolved heavy metal ions and form insoluble precipitates. The resultant precipitates are filtered out by the soil matrix within and down gradient of the reactive zones. In the case of nitrates, the anaerobic conditions formed within the reactive zones convert the nitrate first to nitrite and then to nitrogen gas which is eventually stripped out of the groundwater.

Claims

1. A method for removing contaminants dissolved in ground water, comprising the steps of:

establishing an injection well from the ground surface to a saturated zone contaminated with heavy metal compounds;

placing a conduit within said injection well, wherein said conduit has a fluid-permeable section below the water table of said contaminated saturated zone; and

supplying carbohydrates and sulfates capable of being utilized by an indigenous population of microorganisms to said conduit such that said carbohydrates and said sulfates are forced out of said fluid-permeable section into said contaminated saturated zone whereby the indigenous population of microorganism will metabolize said carbohydrates leading to the formation of anaerobic conditions and will metabolize said sulfates to produce sulfide ions which will cause the in-situ precipitation of the heavy metal compounds.

2. The method of claim 1, further comprising the step of mixing said carbohydrates and said sulfates in said injection well.

3. The method of claim 1, further comprising the step of supplying an additional population of microorganisms capable of metabolizing carbohydrates and sulfates to said contaminated saturated zone, wherein said additional population of microorganisms will metabolize said carbohydrates leading to the formation of anaerobic conditions and will metabolize said sulfates to produce sulfide ions which will cause the in-situ precipitation of the heavy metal compounds.

4. The method of claim 1, wherein the step of supplying carbohydrates and sulfates comprises the steps of placing a pump in fluid communication with said conduit and operating said pump to force said carbohydrates and said sulfates out of said fluid-permeable section of said conduit.

5. The method of claim 1, wherein the step of supplying carbohydrates and sulfates comprises supplying molasses extract to said conduit.

6. A system for removing dissolved contaminants from ground water, comprising:

an injection well extending from a ground surface to below the water table of said ground water;

a conduit within said injection well, wherein said conduit is substantially impermeable above said water table and has a fluid-permeable section below said water table;

a supply of carbohydrate and sulfates; and

a pump in communication with said conduit for supplying said carbohydrates and sulfates under pressure sufficient to force said carbohydrates and sulfates out of said fluid-permeable section and into said ground water where the indigenous population of microorganisms will metabolize said carbohydrates leading to the formation of anaerobic conditions and will metabolize said sulfates to produce sulfide ions which will cause the in-situ precipitation of heavy metal compounds.

7. The apparatus of claim 6, further comprising a mixing pump within said conduit for mixing said carbohydrates and sulfates.

8. The apparatus of claim 6, further comprising a supply of carbohydrate and sulfate metabolizing microbes.