# Patent

## Title
Bioventing remediation system

## Abstract

Bioventing systems create a bacterial treatment zone at a contaminated site by supplying a hydrocarbon food source to the treatment zone, and recirculating the hydrocarbon to the treatment zone. The bioventing systems may inject, circulate, extract and reinject hydrocarbons such as butane or other alkanes to the subsurface at a contaminated site to create a bacterial treatment zone. Contaminated vapors extracted from the soil and/or groundwater may be reintroduced into the site. Hydrocarbons that are not consumed by the bacteria in the treatment zone may be extracted and recovered for recirculation into the treatment zone.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/403,934 filed Aug. 16, 2002.


FIELD OF THE INVENTION
The present invention relates to remediation of sites contaminated with pollutants such as petroleum pollutants, chlorinated solvents and the like. More particularly, the invention relates to bioventing systems for remediating such sites.
BACKGROUND INFORMATION
Gasoline and other volatile organic compounds such as chlorinated aliphatic hydrocarbons released into the subsurface may become distributed into different phases such as an adsorbed phase (on soil surface), a vapor/volatilization phase (in soil gas), a dissolved phase (in groundwater) and a free phase (e.g., a pure petroleum or chemical product floating on the groundwater table as a light non-aqueous phase liquid (LNAPL) or sinking below the water table as dense non-aqueous phase liquid (DNAPL).
Soil vapor extraction (SVE) is a physical means of removing or reducing concentrations of volatile organic compounds (VOCs) that partition into the vapor phase. SVE technology was developed to remove volatiles from the subsurface. This technology targets the adsorbed, vapor and NAPL phases of the VOCs present in the unsaturated (vadose) portion of the subsurface. Dissolved-phase VOCs found beneath the groundwater table is not directly addressed by using an SVE system.
Remediation by SVE involves applying a vacuum to soils in the unsaturated zone above the water table in order to induce airflow. Contaminated mass removal is achieved by drawing contaminant-free air into the soil void spaces. The contaminant-free air creates a concentration gradient and the compounds diffuse into the air stream. This VOC-laden air is continuously extracted and replaced with contaminant-free air. An additional benefit of SVE is the continuous flow of oxygen into the area where hydrocarbons are adsorbed on the soil. This continuous oxygen supply enhances the biodegradation of the hydrocarbons within the soil matrix.
A typical SVE system consists of one or more vapor extraction wells strategically located. The SVE wells can be placed vertically or horizontally, depending on depth to groundwater and other site-specific characteristics. The piping system is commonly placed underground, primarily to provide extra protection from accidental damage. The piping system usually ends at a common header pipe, which is connected to a blower or a pump depending on the flow and vacuum desired. An air/water separator and or filter is required prior to the vacuum pump in order to protect equipment from moisture and particulates drawn into the system. Discharge from the blower or vacuum pump is either vented to the atmosphere or connected to an off-gas treatment system, depending upon emissions requirements and the nature and extent of VOCs.
SVE alone is not effective for removing heavier material such as diesel fuel, jet fuel or fuel oils, because of the nonvolatile high-molecular weight fractions they contain. Venting techniques have been developed which utilize SVE hardware and vertical piping as a means of introducing or injecting and reinjecting air (oxygen) into the treatment zone. Such venting techniques may be appropriate when the water table is deep and the contaminant has not reached the groundwater.
In-situ air sparging, also known as in-situ air stripping or in-situ volatilization, is a technology utilized to remove VOCs from the subsurface saturated zone. In-situ air sparging, when utilized with an SVE system, may greatly extend the utility of SVE to the saturated zone. Air sparging is a process in which contaminant-free air is injected under pressure (sparged) below the water table of an impacted aquifer system. In air sparging applications, the air injection pressure is the sum of the hydrostatic pressure (also known as breakout pressure), which is a function of submersion depth of the air sparging point, and the air entry pressure of the geologic formation, a function of capillary resistance to pore water displacement.
Volatile compounds exposed to the injected air are transferred to the vapor phase, similar to air stripping. Once captured by an SVE system, the VOC-laden air is transferred to a subsequent emissions treatment system. Air sparging systems must operate in tandem with SVE systems intended to capture this VOC-laden air stream. Implementing an air sparging system without an SVE system can potentially create a net positive pressure in the subsurface, inducing groundwater migration into areas previously less affected by dissolved-phase VOCs. Air sparging systems may also add oxygen to the groundwater, thus accelerating the natural biological decay process.
The primary mechanisms responsible for VOCs removal during operation of air sparging systems are believed to be in-situ stripping of dissolved-phase VOCs, volatilization of dissolved-phase and adsorbed-phase VOCs beneath the water table and in the capillary fringe, and aerobic biodegradation of both dissolved-phase and adsorbed-phase VOCs as a consequence of additional oxygen supplied by the injected air. When an air sparging system is optimized for stimulating biodegradation, it is sometimes referred to as biosparging. Typically biosparging systems are initially operated for volatilization and stripping. The system is then fine-tuned for enhancement of biodegradation.
SUMMARY OF THE INVENTION
The present invention provides bioventing systems which create a bacterial treatment zone at a contaminated site by supplying a hydrocarbon food source to the treatment zone, and recirculating the hydrocarbon to the treatment zone. The bioventing systems may inject, circulate, extract and reinject hydrocarbons such as butane to the subsurface at a contaminated site to create a bacterial treatment zone. In one embodiment, contaminated vapors extracted from the soil and/or groundwater are reintroduced into the site. Hydrocarbons that are not consumed by the bacteria in the treatment zone may be extracted and recovered for recirculation into the treatment zone. Butane is a particularly preferred hydrocarbon food source which stimulates the growth of butane-utilizing bacteria. However, other hydrocarbons, such as other alkanes and the like, may be used as a bacterial food source in addition to butane or in place of butane.
The bioventing system may be used to recirculate butane and/or other hydrocarbons at various locations such as in the unsaturated zone (above the water table), below the water table and/or at the capillary fringe (water table interface). The bioventing system may be used to remediate and restore contaminated soil and/or groundwater. When used to remediate soil alone, the butane may be reinjected above the water table. For arid or dry soils, it may be desirable to inject water in sufficient amounts to provide moisture to promote bacterial growth.
An aspect of the present invention is to provide a bioventing system comprising a source of hydrocarbon, an injector in flow communication with the source of hydrocarbon and a treatment zone, and an extraction vent communicating with the treatment zone.
Another aspect of the present invention is to provide a method of remediating a contaminated site comprising introducing a hydrocarbon bacterial food source to a treatment zone of the site, and extracting at least a portion of the hydrocarbon food source from the treatment zone.
These and other aspects of the present invention will be more apparent from the following description.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is partially schematic elevation view of a bioventing system in accordance with an embodiment of the present invention.
FIGS. 2 and 3 are graphs illustrating petroleum contaminant levels at a site treated with a bioventing system as shown in FIG. 1, before and after treatment with the bioventing system.
FIG. 4 is a partially schematic plan view of a bioventing system in accordance with another embodiment of the present invention.



DETAILED DESCRIPTION
FIG. 1 schematically illustrates a bioventing system 10 in accordance with an embodiment of the present invention. The bioventing system 10 includes a supply of butane 12 or other hydrocarbon bacterial food source and an air intake 14 connected to a compressor 16. Butane and air are fed to a mixing panel 18 which controls the flow of the butane and air to injection wells 20 in the treatment zone. Extraction wells 22 recover a portion of the butane as well as other liquids or gases from the treatment zone. A blower 24 is used to recirculate the recovered materials back to the treatment zone via recirculation injectors 26.
In one embodiment, the butane injection system may operate concurrently with an extraction system, such as a SVE system which is used to maintain a vacuum within vadose zone soils. Effluent from the SVE system may be piped back into the biobutane treatment zone, thus allowing vapor control while reducing operation costs by eliminating the need for carbon replacement or regeneration and by recycling the butane gas. The SVE system may further oxygenate the soil, resulting in enhanced microbial degradation of pollutants such as petroleum compounds. Butane injection may also be applied to traditional bioventing systems that are simply recirculating air into a treatment zone.
The following examples illustrate various aspects of the invention, and are not intended to limit the scope of the invention.
EXAMPLE 1
A butane injection panel was installed at a petroleum contaminated service station in Massachusetts. Three years prior to the installation, the site soil and groundwater were impacted by a release from a leak in a product line associated with a UST. The release also produced gasoline vapors that were detected in a building adjacent to the property. Drilling activities revealed the presence of VOCs in soil and contaminants on the water table. Initially, attempts were made to remediate the site by removing material via an ORS product recovery well and product recovery tank, as well as removal of 500 yards of contaminated soil, followed by installation of a conventional soil vapor extraction (SVE) system. The SVE system operated for 18 months and was shut down without successful remediation of the site. Subsequently, a biofeasibility study was conducted using site-specific groundwater. The data obtained from the study confirmed that butane-utilizing bacteria capable of effectively degrading the target pollutants existed at the site.
A butane injection system was then combined with the existing SVE system, as illustrated in FIG. 1. The butane injection system may be similar to those described in U.S. Pat. Nos. 5,888,396, 6,051,130, 6,110,372, 6,156,203, 6,210,579, 6,244,346 and 6,245,235, which are incorporated herein by reference. The butane injection system is used to stimulate the growth of butane-utilizing bacteria which degrade pollutants in the treatment zone. Examples of butane-utilizing bacteria are described in the aforementioned patents. The butane injection system may operate concurrently with the SVE system, which is used to maintain a vacuum within vadose zone soils to control potential migration of VOCs from the treatment area into adjacent buildings. The SVE system was converted to operate as a bioventing system to further oxygenate soils resulting in enhanced microbial degradation of petroleum compounds in the capillary fringe and vadose zone. The off-gas from the system is piped back into the biobutane treatment zone, thus allowing vapor control while reducing the overall operation and maintenance costs by eliminating the need for carbon replacement or regeneration, and by recycling the butane or other hydrocarbon gas.
Table 1 and FIGS. 2 and 3 show the results of the bioventing process.







TABLE 1







Groundwater Test Data














C5-C8
C9-C12
C9-C10
C9-C18
C19-C36
C11-C22



Ali-
Ali-
Aro-
Ali-
Ali-
Aro-



phatic
phatic
matic
phatic
phatic
matic

















Initial
54
830
1200
19000
2400
30000


Levels


Final
0
0
583
0
0
0


Levels









EXAMPLE 2
A total of six butane/air sparge wells were installed in a treatment area as illustrated in FIG. 4. Each butane/air sparge well may consist of 1-inch or 11⁄4-inch inside diameter, black iron pipe or Schedule 80 PVC fitted with a 2-foot slotted screen, advanced from the ground surface to a clay deposit identified across the site at a depth of 9 feet below grade. FIG. 4 illustrates the location of the injection wells labeled BAI-1 through BAI-6.
These wells were piped to a butane injector located in a treatment shed in the northern portion of the site, as shown in FIG. 4. An objective of the injection system is to oxygenate the groundwater without the customary effects and contaminant dispersal associated with aggressive air-sparging programs. The butane injector pulses butane gas at a selected volume into the flow stream of an air sparging well supplied with air by a compressor. The airflow was controlled to each well using valves. The airflow rate in each air sparge well is anticipated to vary between 3 and 5 cubic feet per minute. In addition, it is anticipated that in order to generate a dissolved butane concentration in groundwater of 10 to 20 ppm in the treatment zone, approximately 2.0 lbs (site total) of liquid butane was injected (as a gas) into the site aquifer daily (approximately 12.8 ft3).
The SVE system previously installed at the site was operated concurrently with the butane biostimulation treatment system and used to maintain a vacuum within vadose zone soils. The SVE system served as a control for potential migration of volatile organic compounds (VOCs) from the treatment area into adjacent buildings. In addition, the SVE system further oxygenated the soils thus resulting in enhanced microbial degradation of petroleum compounds in the capillary fringe and in the vadose zone. VOCs were monitored in each vapor extraction well using a photoionization detector (PID) during site monitoring visits.
The effluent from the SVE system was piped back into the butane biotreatment zone, as shown in FIG. 4, thus allowing for vapor control while reducing the overall O&M costs by eliminating the need for carbon replacement or regeneration and by recycling the butane gas.
The recirculated effluent from the SVE system was monitored using a PID meter during site visits. The level of VOCs concentration measured by the meter is a very good indication of the effectiveness of the butane biotreatment system with particular emphasis on the soil contamination located in the vadose or unsaturated zone. The results of the effluent screening are summarized in Table 2 below.







TABLE 2







VOCs Content of SVE System Effluent










Date of Soil Gas Screening
PID Results (ppm)














Before Butane Bioventing
690



4 Months After Initiation of
95



Butane Bioventing



7 Months After Initiation of
93



Butane Bioventing










The results clearly indicate that the VOCs concentrations in the soil gas were significantly decreased by continuous reinjection into the butane biotreatment zone established in the vadose zone soils. The soil gas represents the SVE system blower effluent prior to reinjection into the subsurface. This is the soil gas effluent normally piped into granular activated carbon canisters for treatment and eventual disposal.
Table 3 is a summary of the groundwater quality data from the site. Butane bioventing was initiated in Month No. 7. Significant improvements in groundwater quality were achieved. It is noted that the GP-3 monitoring well was believed to be located upgradient of the treatment zone of influence.







TABLE 3







Summary of Groundwater Quality Data (System Startup Month No. 7)

















Sample
Analytical






C5-C8
C9-C12
C9-C10


Location
Method
Benzene
Ethylbenzene
MTBE
Naphthalene
Toluene
Xylenes
Aliphatics
Aliphatics
Aromatics




















Month No. 1












GBI-1
MADEP VPH
ND
ND
10.1
ND
ND
ND
ND
ND
ND


GBI-2
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-3
MADEP VPH
ND
ND
196
ND
ND
ND
ND
ND
ND


GBI-4
MADEP VPH
ND
ND
289
ND
ND
122
1,460
1,140
ND


VW-1
MADEP VPH
ND
ND
15,700
ND
120
2,404
22,600
27,800
2.440


VW-2
MADEP VPH
ND
1,510
109,000
ND
504
4,090
37,600
46,900
ND


VW-3
MADEP VPH
2,170
3,130
12,700
ND
34,600
18,110
ND
12,200
ND


VW-4
MADEP VPH
247
1,540
2,500
517
799
10,250
6,610
ND
5,260


VW-6
MADEP VPH
942
1,260
7.800
332
85.8
3,740
18,500
8,470
3.800


VW-7
MADEP VPH
ND
ND
6.13
ND
ND
ND
ND
ND
ND


TRIP
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GP-3
MADEP VPH
1,380
689
140,000
473
9,740
17,520
ND
ND
6,770


Month No. 5


GBI-1
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-2
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-3
MADEP VPH
ND
ND
41
ND
ND
ND
ND
ND
ND


GBI-4
MADEP VPH
ND
ND
200
ND
ND
ND
220
19
160


VW-1
MADEP VPH
ND
ND
16,000
ND
ND
ND
ND
930
ND


VW-2
MADEP VPH
400
ND
24,000
ND
ND
580
620
2,400
960


VW-3
MADEP VPH
130
300
72
130
3,200
1,590
4,800
310
1,900


VW-4
MADEP VPH
360
1,600
7,100
340
440
9,600
1,700
3,600
10,000


VW-6
MADEP VPH
690
1,500
4,500
160
110
3,250
1,900
1,900
6,300


VW-7
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


TRIP
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GP-3
MADEP VPH
ND
ND
74,000
ND
ND
1,500
ND
3,500
3,400


Month No. 8


GBI-1
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-2
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-3
MADEP VPH
ND
ND
497
ND
ND
ND
ND
ND
ND


GBI-4
MADEP VPH
26.8
ND
923
24.9
5.7
14.4
ND
81.6
301


VW-1
MADEP VPH
717
ND
10,600
ND
14.8
321
ND
ND
155


VW-2
MADEP VPH
1.472
292
41,900
337
713
4,012
ND
ND
3,680


VW-3
MADEP VPH
527
820
770
271
11,400
7,040
ND
ND
3,610


VW-6
MADEP VPH
126
1,810
8,700
283
467
3,719
ND
ND
3,810


VW-7
MADEP VPH
38.2
ND
11.5
ND
ND
10
ND
ND
ND


TRIP
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GP-3
MADEP VPH
4,320
1,000
83,300
947
16,900
31,900
ND
ND
9,440


Month No. 11


GBI-1
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-2
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-3
MADEP VPH
ND
ND
1,530
ND
ND
ND
ND
ND
ND


GBI-4
MADEP VPH
ND
ND
922
ND
ND
62.6
908
ND
ND


VW-1
MADEP VPH
ND
ND
5,254
ND
ND
ND
ND
ND
ND


VW-2
MADEP VPH
216
ND
35,200
ND
675
1,500
ND
ND
3,690


VW-3
MADEP VPH
ND
771
587
ND
182
753
ND
ND
3,220


VW-6
MADEP VPH
1,250
1,930
10,600
ND
ND
4,068
ND
ND
9,030


VW-7
MADEP VPH
ND
ND
56.4
ND
ND
ND
ND
ND
ND


TRIP
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GP-3
MADEP VPH
3,950
1,610
210,000
ND
16,600
24,750
ND
ND
19,600


Month No. 14


GBI-1
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-2
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GBI-3
MADEP VPH
ND
ND
6,790
ND
ND
ND
ND
15.4
ND


GBI-4
MADEP VPH
32
28.7
2,510
ND
58
48.7
ND
33.6
352


VW-1
MADEP VPH
5.2
5.4
103
29.3
ND
40.9
ND
ND
303


VW-2
MADEP VPH
551
271
13,100
435
44.3
1,331
ND
1,500
4,710


VW-6
MADEP VPH
513
799
5,170
418
116
1,073
ND
888
3,740


VW-7
MADEP VPH
ND
ND
385.0
ND
ND
ND
ND
39.4
ND


TRIP
MADEP VPH
ND
ND
ND
ND
ND
ND
ND
ND
ND


GP-3
MADEP VPH
740
958
41,400
ND
243
16,920
ND
ND
14,500
















GW-2 STANDARD
2,000
30,000
50,000
6,000
6,000
6,000
1,000
1,000
5,000


GW-3 STANDARD
7,000
4,000
50,000
6,000
50,000
50,000
4,000
20,000
4,000





All concentrations expressed in μg/l (ppb)


Bold values exceed GW-2 and/or GW-3 Standards


VW-4 was dry on Jan. 24, 2002, Apr. 24, 2002 and Jul. 31, 2002


VW-3 was dry on Jul. 31, 2002






Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention.

## Claims

1. A system comprising:
a source of hydrocarbon comprising at least 50 weight percent butane;
an injector in flow communication with the source of hydrocarbon and an in-situ treatment zone;
an extraction vent communicating with the in-situ treatment zone; and
means for recirculating at least a portion of the hydrocarbon to the in situ treatment zone.

2. The system of claim 1, wherein the butane comprises at least 90 weight percent of the hydrocarbon.

3. The system of claim 1, wherein the in situ treatment zone comprises soil.

4. The system of claim 1, wherein the in situ treatment zone comprises groundwater.

5. The system of claim 1, wherein the extraction vent is in flow communication with the injector for recirculating at least a portion of the hydrocarbon to the in situ treatment zone.

6. The system of claim 1, further comprising means for introducing oxygen to the in situ treatment zone.

7. The system of claim 1, further comprising:
a source of oxygen; and
an oxygen injector in flow communication with the source of oxygen and the in situ treatment zone.

8. The system of claim 7, wherein the oxygen is provided in the form of air.

9. A system comprising:
a source of hydrocarbon comprising at least 50 weight percent butane;
an injector in flow communication with the source of hydrocarbon and an in situ treatment zone; and
an extraction vent communicating with the in-situ treatment zone, wherein the extraction vent is in flow communication with the injector for recirculating at least a portion of the hydrocarbon to the in situ treatment zone.