Accelerated Bioremediation as an Alternative to Conventional Remedial Technologies.

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ABSTRACT: Application of bioremediation as an alternative technology to expedite soil and ground-water remediation has been effective in reducing the concentration of hydrocarbons at an affordable cost. Bioremediation processes can be achieved by the addition of biological organisms into the soil and ground water which are contaminated and are microorganism deficient. The microorganism's activities can also be increased by adding nutrients. A combination of microorganisms and nutrients was injected in low permeability soil contaminated with hydrocarbons using geoprobe drilling equipment. Ground-water samples collected prior to the injection and five months after the first application of microorganisms (Micro-Bacâ International, Inc.) and Oxygen Release Compounds (ORCâ , Regenesis, Inc.) showed a significant decrease in dissolved hydrocarbon concentrations in most of the monitoring points. Additional ground-water sampling conducted after seven months of application showed, in most of the areas, that the bioremediation process was still active. The reduction in hydrocarbon concentrations was obtained at a low cost if compared with other remedial technologies which are currently used for similar projects.

INTRODUCTION

Hydrocarbon components from releases of petroleum products into the subsurface are in general degraded by the native microorganisms located in soil and ground water. An increase of biological activity by introducing microorganisms and nutrients can accelerate the biodegradation process of hydrocarbons and remediate the soil and ground water. The following is a description of bioremediation treatment using microorganisms and ORC in order to accelerate the biodegradation process of hydrocarbon compounds at a significant reduction in cost.

SITE DESCRIPTION/MATERIALS AND METHODS

The site (105’ X 45’) is a former gasoline in New York, NY. Following the removal of the underground storage tanks (USTs), a soil-vapor extraction (SVE) system was installed in the former UST excavation which was backfilled, paved and used as a parking lot. Additional subsurface investigations were conducted and concluded that the fine grained sediments mixed with building debris encountered beneath the site continued to exhibit high levels of hydrocarbons and that the ground water which was found at 22 ft bg (feet below grade) also contained dissolved hydrocarbons. The data suggested that the SVE reached the point of diminishing return and for that reason was removed from the site.

After analysis of several additional remedial technologies, bioremediation was selected for this site because it has the potential for significant reduction of hydrocarbon concentrations while causing minimal site disturbance. Soil samples was analyzed in the field for pH and moisture percentage and submitted to a laboratory for analysis of volatile organics, by EPA Method 8020 modified to include MTBE as well as heterotrophic plate counts (HPC) and total organic carbon (TOC). Ground-water samples were analyzed in the field for dissolved oxygen, eH, pH, conductivity, dissolved solids and then analyzed for contaminants as described for soil In order to determine the bioremediation applicability each ground-water sample was also analyzed for nitrate, ammonium, orthophosphate, chemical oxygen demand, sulfate and RCRA metals.

Two types of bioremediation treatment were used at the site. The first treatment consisted of injecting microorganisms into the vadose zone using the Geoprobe drilling unit The second bioremediation treatment consisted of an ORC slurry injection beneath the ground-water level also using the Geoprobe borings. The application of ORC into the ground-water plume was done in order to increase the aerobic biodegradation of the contaminants and to provide additional impact of oxygen to the microorganisms which are the engine of bioremediation process.

The first application of microorganisms and ORC at the site was conducted in April 1997. Eight test borings drilled by geoprobe method were used and a liquid containing microorganisms supplied by Micro-BacR International, Inc. was injected in four borings above the ground-water level; a slurry of ORC manufactured by Regenesis was injected below the ground-water level using four different borings. Data was collected at five months and seven months after the first bioremediation treatment was applied.

RESULTS

Field Results: Bioremediation results are presented in Table 1 and Figure 1. With respect to Table 1, a comparison between the application of microorganisms versus ORC was made in order to determine which application has the potential to accelerate the bioremediation process. The data indicates that following microbe application at Injection Point TB-1 the benzene concentration in ground water decreased in five months by 54% and at seven months to 84%. Values for total BTEX were 44% after five months with a small increase to 40% by Month 7. Similarly, for injection point, TB-6, there was a benzene reduction of 14% after five months and a total of 21% after seven months. The total BTEX was reduced 41% after five months and a small increase to 41% after two more months. The data suggested that the microbe application have been successful in accelerating the bioremediation process during the first five months.

The ORC application shows a similar pattern for benzene (TB-3 and TB-5 injection points) and a higher reduction of total BTEX. For example, at Injection Point TB-3, the total BTEX reduction after five months of ORC application was 80% and increased to 95% after two more months. The data from a second ORC application point (TB-5) showed a smaller reduction of total BTEX (34%) after 5 months but continued to indicate that the bioremediation process was still active after 7 months (51% reduction) following the ORC application.

The data suggest that the ORC application was more efficient then the microbe application. Because the results are completely based on ground-water samples and the ORC application was conducted below the ground-water level while the microorganisms were injected in the vadose zone the effect of ORC application is higher to the ground water. The injection of microorganisms and ORC in two adjacent geoprobe borings at the site stimulated biodegradation and finally resulted in a reduction of the hydrocarbon concentrations in ground water. In addition, the bioremediation treatment reduced the distance where the plume migrates at concentrations that pose a risk to the environment.

A contour map illustrating the overall impact of the treatments on total BTEX at baseline, Month 5 and Month 7 is presented in Figure 1. The highest BTEX concentration prior to the first application was in the TB-3 area. The extent of the plume showing BTEX concentrations between 30,000 and 200,000 ug/l was approximately 40 feet long. After five months, following the application of bioremediation treatment in eight injection points the 30,000 ug/l BTEX concentration plume was reduced to 30 feet. The concentration of dissolved BTEX was reduced substantially in most of the injection points and the plume started to show that the application process was very efficient in the core of the contamination plume.

By November 1997, after seven months of the accelerated bioremediation treatment, the configuration of the dissolved plume indicates that while the concentration of the plume remained in the same location a significant reduction of dissolved BTEX was obtained. The results of ground-water analysis showed that the bioremediation treatment was efficient and a significant reduction of hydrocarbon plume was obtained beneath the site.

Cost Comparison: The cost of the bioremediation treatment was compared with the cost for other remediation technologies which were determined to be feasible for these site conditions. Remediation techniques like soil excavation and disposal, ground-water pumping and treat, and on-site thermal treatment are not feasible because of site conditions (i.e., access, low aquifer yield, low ground-water levels, high cost) and were eliminated. The costs for implementation of remedial technologies as soil-vapor extraction, air sparging/soil-vapor extraction (AS/SVE) and high vacuum extraction were evaluated in comparison with the bioremediation treatment.

Table 2 lists the capital and operations and maintenance costs for each of these remediation technologies. Capital cost for bioremediation treatment includes drilling of Geoprobe borings and application of microbe and ORC treatment for six times during a three-year period. However, based on results obtained at the Manhattan site, it is expected that the bioremediation treatment will take less than three years.

The operation and maintenance cost for the other remediation technologies include monthly visits and sampling of remediation system and quarterly ground-water sampling for a five-year period. The operation and maintenance cost for bioremediation treatment is related to quarterly ground-water sampling and analysis for five years.

CONCLUSIONS

The results of bioremediation treatment indicate that this technology was very effective for remediation of soil and ground water with hydrocarbon components at this site. Significant reduction of BTEX in ground water was obtained by using Geoprobe points for injecting microorganisms and Oxygen Release Compound above or below the ground-water level. The bioremediation technology has the potential to reduce hydrocarbon concentrations from soil and ground water while causing minimal site disturbance. This remediation technology has a low cost, and depending on subsurface conditions, in some cases is more efficient than other available technologies.

 

TABLE 1. Water quality summary.

Sample ID
Date
Benzene (ug/l)
Toluene (ug/l)
E-benzene (ug/l)
Xylenes (ug/l)
BTEX (ug/l)
MTBE (ug/l)
TB-1
4/2/97
7,000
23,000
4,000
20,100
54,100
1,300
TB-1
8/27/97
3,200
14,000
2,000
11,000
30,200
<500
TB-1
11/17/97
1,100
11,000
3,200
17,000
32,300
180
 
TB-3
4/2/97
6,200
52,000
26,000
122,000
206,200
10,000
TB-3
8/27/97
3,200
5,100
6,000
25,000
39,300
6,900
TB-3
11/17/97
3,100
1,600
2,300
2,900
9,900
4,800
 
TB-5
4/2/97
20,000
43,000
5,600
24,500
93,100
33,000
TB-5
8/27/97
14,000
21,000
5,100
21,000
61,100
4,900
TB-5
11/17/97
13,000
17,000
3,400
12,000
45,400
5,600
 
TB-6
4/2/97
14,000
47,000
6,400
31,600
99,000
22,000
TB-6
8/27/97
22,000
22,000
3,300
15,000
52,300
3,800
TB-6
11/17/97
22,000
22,000
4,300
21,000
58,300
2,400
 
TB-7
4/2/97
670
6,600
2,400
10,900
20,570
540
TB-7
8/27/97
230
490
150
490
1,360
76
TB-7
11/17/97
1,200
14,000
3,200
16,000
34,400
300
 
TB-8
4/2/97
<1
270
1,200
3,800
5,270
1,000
TB-8
8/27/97
6
25
330
850
1,211
590
TB-8
11/17/97
<1
8
2
11
21
3,300
 
TB-11
4/2/97
<1
2
<1
5
7
<1
TB-11
8/27/97
1
21
15
120
157
1
TB-11
11/17/97
42
240
72
380
734
4
 
TB-13
4/2/97
<1
<1
<1
<1
<1
7,100
TB-13
8/27/97
2
4
2
12
20
4,900
TB-13
11/17/97
50
910
3,100
13,000
17,060
580

 

TABLE 2. Cost comparison of remediation technology.

Remediation
Technology
Capital Cost
Total Capital Cost
 
Wells, Trenching and Piping
Equipment, Material, Permits and Air Treatment
Bioremediation Treatment
 

Soil-Vapor Extraction (SVE)

$27,000
$19,000
--
$46,000

Air Sparging/SVE

$31,000
$25,000
--
$53,000
High Vacuum Extraction (HVE)
$27,000
$51,500
--
$78,500
Bioremediation Treatment*
--
--
$48,000
$48,000


Remediation Technology
Operation and Maintenance
Total O&M
 
Monthly O&M
Quarterly Ground-Water Monitoring
Years
 
Soil-Vapor Extraction (SVE)
$ 1,000
$ 2,000
5
$100,000
Air Sparging/SVE
$ 1,500
$ 2,000
5
$130,000
High Vacuum Extraction (HVE)
$ 2,000
$ 2,000
5
$160,000
Bioremediation Treatment
$ 0
$ 2,000
3
$ 24,000**

* 6 applications in 3 years
** Based on only 3 years O&M:

TOTAL COST - CAPITAL AND O&M

Soil-Vapor Extraction (SVE): $146,000

Air Sparging/SVE: $183,000

High Vacuum Extraction (HVE): $238,500

Bioremediation Treatment with ORC: $ 72,000

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