Remediate BTEX Sites Using Oxygen
So You Can Avoid
Over-Spending
Lower your bioremediation costs with this simple, low maintenance solution.
Is This Solution a Good Fit For Remediating Your BTEX Site?
BTEX Bioremediation Efforts have never been easier, with this proven, low cost method.
If your answer is YES to these 4 Questions, the Waterloo Emitter is a good fit!
Is BTEX Concentration 10 ppm or less?
Would you like to drastically reduce your Remediation Costs?
Are you using 2", 4" or 6" Wells?
Would you prefer to deploy a very low maintenance solution?
- Enhanced Biormediation
The Waterloo Emitter™ is designed to assist remedial biodegradation of BTEX and other contaminants. It enables oxygen to diffuse through silicone or LDPE tubing in a controlled uniform manner.
- Steady, Direct Diffusion of Oxygen
Emitters are ideal for the bioremediation of BTEX using oxygen. The diffusive process provides immediate bioavailability of molecular oxygen for aerobic biodegradation enhancement.
Engineered for the ControlledContinuous Diffusive Release of:
- Oxygen for aerobic bioremediation
-
Hydrogen for anerobic bioremediation
-
CO2 for pH adjustment
-
SF6, He, Ar for tracer tests
Remediation of a Former Gas Station Site - Within 6 Months!
Vertex Environmental Inc., located in Cambridge, Ontario, specializes in the in-situ remediation of contaminated groundwater. In 2007 they were contracted to clean up a former gas station site in Guelph, Ontario. The contaminant plume containing gasoline and diesel occurs in unconsolidated silty sand to a depth of approximately 3 m (10 ft). The initial plume stretched 30 m (100 ft) long and 15 m (50 ft) wide. Migration towards down gradient receptors was a concern, therefore a solution that worked quickly and effectively was required to help eliminate the potential for exposure. Waterloo Emitters were chosen for the site to diffuse oxygen into the contaminant plume, thereby enhancing the natural biodegradation of BTEX and Petroleum Hydrocarbons (PHCs).
“The Emitters created an effective aerobic reactive zone that attenuated the dissolved petroleum hydrocarbons to below detection limits within a short period of time thus protecting down gradient receptors”
Rick McGregor, M.Sc., MBA, CGWP, P.Geo. Hydrogeologist/Geochemist Vertex Environmental Inc.
Acknowledgement: Solinst thanks Rick McGregor of Vertex Environmental Inc. for providing the details of this application.
This entry was posted in Aerobic Bioremediation and tagged remediation, rick mcgregor, btex remediation, enhanced bioremediation, petroleum hydrocarbons, in-situ remediation, 703 waterloo emitter, contaminated sites on March 23, 2009 by solinst.
FAQs Frequently Asked Questions
QUESTION: How do you maintain the operating pressure of O2 up enough to maintain constant diffusion through the tubing?
ANSWER: We use a simple regulator to control pressure and manual venting of the lines periodically to refresh the gas within the tubing (vent out gases that diffuse from the water INTO the tubing). The use of an automated gas management control system is advised which would include the following basic features: control oxygen pressure (and allow it to be varied by the operator); allow venting of the oxygen lines for brief a period ideally one or more times a day but no less frequently than weekly (operator should be able to adjust this frequency); the duration of the period of venting may depend on the configuration of the supply and venting system, number of emitters, etc. The idea is to be sure to blow out all the gases in the tubing of each emitter and thus refresh them with pure oxygen. allow control of a reasonably large number of emitters with one control system , e.g. up to 10 well’s worth of emitters (more than one emitter could be in each well, but would be connected in series and act like one emitter). Thus if an application required more than 10 well locations, the application should likely be divided into a number of separate CHANNELS, each of which would be separately controlled, vented and monitored have some ability to shut down any channel which develops a leak ideally have ability to alert operator if: pressure to emitters rises beyond specified maximum levels (LDPE = 90psi, Silicone tubing = 25psi) pressure to emitters decreases below a specified minimum level, e.g. due to a leak, exhaustion of oxygen supply, etc.
QUESTION: Have you determined the effects of erosion of the tubing by water, aging of tubing material, or biofouling of the surface for any long-term operation?
ANSWER: Neither polymer has shown signs of aging (i.e. deteriorating performance) over 1.5 years of field use. A reasonable estimate of useful life for silicone tubing would be 2-3 year life under typical operating conditions and groundwater environments (ie. only dissolved contaminants present). It is expected that LDPE would last up to approximately 5 years life under typical operating conditions and groundwater environments.
QUESTION: Any idea on how often the coils need to be serviced or replaced?
ANSWER: The PVC frame should not need replacing, only the polymeric diffusive tubing would need to be replaced as estimated above.
QUESTION: How often does the system need to be monitored to maintain sufficient oxygen release (once a week, twice a week, etc.)?
ANSWER: The gas supply and management system should have an alarm feature to alert operators of low gas supply pressure, leaks, etc.
Technical Bulletin
Leaking Underground Storage Tanks
Over 482,000 sites across the United States have been identified as contaminated due to leaking underground storage tanks (LUST), according to the U.S. EPA web site. Many old fuel storage tanks have corroded and rusted with time, released their contents, and polluted groundwater with MTBE, BTEX and other petroleum hydrocarbons.
The EPA’s federal underground storage tank (UST) regulations have been in place for over ten years now, and 380,000 of these contaminated sites have been successfully cleaned up. Yet, with thousands of tainted sites remaining and future spills and leaks inevitable, the environment and our drinking water remain at risk.
Enhanced Bioremediation
The nature of remedial approaches for LUST sites has significantly evolved over the years. Monitoring natural attenuation is now often the first choice, if not the only choice for LUST site remediation. However, techniques that enhance natural attenuation processes are commonly being used due to their potential to speed up remedial programs.
Waterloo Emitters
The Waterloo Emitter™ is a simple, low cost remedial device designed to enhance the natural biodegradation of petroleum hydrocarbons in groundwater. The Emitter allows the controlled release of oxygen into impacted groundwater, thus creating the ideal conditions to stimulate aerobic biodegradation.
The Waterloo Emitter provides remediation engineers with numerous benefits including:
- Enhancing a naturally occuring process
-
Elimination of contaminants in place
-
No harmful by-products produced
-
Simple installation, operation and monitoring requirements
-
Minimal site disturbance
-
No electricity required
-
Low Cost
Installing Waterloo Emitters increases dissolved oxygen concentrations and enhances biodegradation
The Technology
Designed to install easily in 2", 4" or 6" wells, the Waterloo Emitter simply consists of silicone or polyethylene tubing coiled around a PVC frame. Single or multiple Emitters can be placed in screened wells or open boreholes, spanning the contaminant plume thickness.
The technology is based on diffusion principles whereby a concentration gradient is set up between the inside of the Waterloo Emitter tubing and the groundwater. The transfer of oxygen takes place on a molecular level, providing a steady, regulated supply that is critical to the proper growth and maintenance of the natural in-situ microbial population.
Since groundwater flow around the Emitter is continuous oxygen, equilibrium is never reached between the tubing and the groundwater. This results in a steady diffusion of oxygen into the groundwater with no decrease in concentration due to bubbling.
Summary
At suitable LUST sites, in-situ groundwater bioremediation techniques have the ability to make clean-up faster, more effective, and less expensive.
The Waterloo Emitter provides remediation professionals with a reliable, low cost device, which can be used on its own, or as part of a multi-phase approach to attenuate petroleum contamination in groundwater. The simple use of oxygen allows the Emitter to enhance naturally occurring aerobic biodegradation.
Detailed groundwater monitoring at LUST sites can be provided by Solinst Waterloo and CMT Multilevel Systems. They monitor multiple depth-discrete zones in a single borehole. Transects of installations offer a more precise estimate of contamination across a site, and the ability to track the attenuation process.
In Situ MTBE Biodegradation Supported by Diffusive Oxygen Release
Ryan D. Wilson,* Douglas M. Mackay, and Kate M. Scow
Department of Earth Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada, and Department of Land, Air and Water Resources, University of California, Davis, California 95616
Abstract:
Microcosm studies with sediments from Vandenberg Air Force Base, CA, suggest that native aerobic methyl tert-butyl ether (MTBE)-degrading micro organisms can be stimulated to degrade MTBE. In a series of field experiments, dissolved oxygen has been released into the anaerobic MTBE plume by diffusion through the walls of oxygen-pressurized polymeric tubing placed in contact with the flowing groundwater. MTBE concentrations were decreased from several hundred to less than 10 g/L during passage through the induced aerobic zone, due apparently to in situ biodegradation: abiotic MTBE loss mechanisms were insignificant. Lag time for initiation of degradation was less than 2 months, and the apparent pseudo-first-order degradation rate was 5.3 day-1. Additional MTBE was added in steps to raise the influent concentration to a maximum of 2.1 mg/L. With each step, MTBE was degraded within the pre-established aerobic treatment zone at rates ranging from 4.4 to 8.6 day-1. Excess dissolved oxygen suggested that even higher MTBE concentrations could have been treated. Continued flow through the treatment zone was repeatedly confirmed through tracer and other tests. These and others' results suggest that it is possible to create permeable in situ treatment zones solely by releasing oxygen to support native microbial degradation of MTBE.
Figure 1: Map of the vicinity of site 60, Vandenberg Air Force Base (VAFB), CA. The fine dashed line encloses all MTBE detections greater than 2 g/L (19). The area enclosed by the heavier dashed line is the estimated extent of detectable BTEX species. Noted on the figure are the locations of some of the monitoring conducted as part of our project, notably transects A-C. The close up reveals orientation and scale of two field experiments: (a) the Longitudinal Trench Facility (LTF) and (b) the Panel Test.
Figure 2: Plan view of the LTF. Note that the pea gravel backfill (clear) is in contact with the formation (stippled) at its up gradient and down gradient ends but is separated from it on the sides by an impermeable geotextile. The approximate locations of various wells are depicted.
Figure 3: Schematic of cylindrical oxygen emitter. The frame (detail to left) is constructed to allow relatively unimpeded horizontal flow of groundwater, thus allowing good contact of the water with the coils of tubing. The tubing supports are notched to hold the inner and outer tubing coils at different radial distances from the center.
Figure 4: MTBE vs time at three points along the flow path into and through the LTF. The schematic to the right indicates the locations of the monitoring points. As noted above the graph, the oxygen supply was on during the first 107 days, off until day 192, and back on for the remainder of the time depicted.
Reproduced with permission from Environ. Sci. Technolo. 2002, 36, 190-199. Copyright 2002 Am. Chem. Soc.
Entire publication available at: http://pubs3.acs.org/acs/journals/toc.page?incoden=esthag&indecade=
0&involume=36&inissue=2
Acknowledgements: The project described above has been funded since December 1997 by the American Petroleum Institute and also in part by grants from the California MTBE Research Partnership, Chevron Research and Technology Company, GeoSyntec Consultants, the Oxygenated Fuels Association (OFA), from the National Institute of Environmental Health Sciences (NIH), and the UC Water Resources Center. The authors are thankful to the numerous individuals at Vandenberg Air Force Base for their considerable in-kind support; to the California Central Coast Regional Water Quality Control Board for their continued interest and support; to G. Durrant, C. Naas, and others at the University of Waterloo for help in the field and the lab; to J. Cullen, D. Mason, and L. Zanini (all formerly with Conor Pacific/EFW) for help at various stages of the field work; and to Isaac Wood and Mark Morando (Santa Barbara) for their service as invaluable field research assistants.
Henry's Law, one of the gas laws, states:
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Henry's Law
H = C / P
where,
H = Henry's constant for O2 in water at a given temperature and pressure ( H is different for every gas, temperature, and solvent)
C = concentration of O2 in water
P = Partial pressure of O2
Practical Implications for O2 bio-enhancement remediation techniques:
The solubility of DO in water will increase with depth to contaminated groundwater plume (i.e. depth is proportional to increased pressure and decreased temperature)
Dissolved Oxygen
Bio-enhancing contaminated groundwater with O2 to raise dissolved oxygen levels is commonly performed to create or enhance a natural aerobic biodegradation of contaminants. At standard ambient temperature and pressure (25ºC, 1bar), the solubility of dissolved oxygen in fresh water is approximately 39 mg/L.
The solubility of oxygen in water is dependent on temperature and pressure:
- Temperature: solubility increases with decreasing temperature
- Pressure: solubility increases with increasing partial pressure of oxygen in accordance with Henry's law
Practical Implications for use of the Waterloo Emitter:
- Once the O2 has diffused through the Waterloo Emitter tubing into groundwater (see Fick's Law), the solubility of O2 in water will increase with depth to contaminated groundwater plume, as depth is proportional to increased pressure and decreased temperature i.e. typically, the deeper a Waterloo Emitter is installed, the more soluble O2 becomes
- When a gas is applied to the Emitter there is a direct correlation between an increase in applied pressure and an increase in the amount of gas that will diffuse into the groundwater, however, diffusion is the only mechanism that allows the amendment to be added to the groundwater (see Fick's Law)
In Situ MTBE Biodegradation Supported by Diffusive Oxygen Release
Ryan D. Wilson,* Douglas M. Mackay, and Kate M. Scow
Department of Earth Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada, and Department of Land, Air and Water Resources, University of California, Davis, California 95616
Fisk's Law
Fick's law states that local differences in solute concentration will result in a net flux of solute molecules moving from high concentration regions to low concentration regions.
The Waterloo Emitter™ emits amendment materials (gas or liquid) via a diffusion mechanism in accordance with Fick's first law. The Waterloo Emitter may be described as a Fickian system whereby a polymeric membrane (silicone or LDPE tubing) separates a zone of higher internal concentration (gas or liquid inside the tubing) from a zone of lower external concentration of the same species in the groundwater.
In other words, when an amendment is introduced into the Waterloo Emitter tubing, a concentration gradient is set up between the inside of the tubing and the groundwater. As such, the amendment diffuses across the tubing membrane from the higher concentration inside the tubing to the lower concentration in the groundwater.
In mathematical terms, the net amount of material diffusing across a unit cross-section (J, flux) perpendicular to a membrane of known thickness (x) is proportional to the change in concentration (C, higher concentration less lower concentration) divided by the thickness of the membrane.
At steady state, Fickian diffusion can be approximated by:
J = D (C Waterloo Emitter – C groundwater) / membrane wall thickness, where D is the diffusion coefficient for the membrane material and is expressed in L2 / t (e.g. cm2/s).
Diffusion coefficient for Waterloo Emitter silicone tubing is 6.7E-07 cm2/s
Diffusion coefficient for Waterloo Emitter LDPE tubing is 1.73E-08 cm2/s
Practical Implications for used of the Waterloo Emitter
- The net flux of liquid or gaseous amendment across the diffusive tubing will be dependent on the background level of amendment (e.g. dissolved oxygen) in groundwater. Therefore, lower background groundwater concentrations will result in a higher flux from the Waterloo Emitter™
- For liquid amendments, the net flux of liquid amendment across the diffusive tubing will be dependent on the concentration of the liquid amendment used. Therefore, higher concentrations correspond to a higher chemical gradient which will result in a higher flux from the Waterloo Emitter
-
For gaseous amendments, the net flux of gaseous amendment across the diffusive tubing will be dependent on the pressure (which is proportional to the concentration) within the diffusive tubing of the Waterloo Emitter. Therefore, higher pressure will result in a higher flux from the Waterloo Emitter ™)
-
In gas release applications, mass is released from the tubing on a molecular basis and immediately dissolves in the groundwater thus there are significantly reduced mass transfer limitations compared to commonly used gas sparging (bubbling) techniques
-
Diffusion will occur until there is equilibration inside and outside of the tubing. With the Waterloo Emitter, the amendment can be replenished constantly and, since groundwater flow around the Emitter is continuous, equilibration is never reached. This results in steady, controlled diffusion into the groundwater, without any decrease in concentration due to bubbling
-
When oxygen is used as the amendment gas, it provides a regulated supply of dissolved oxygen that is critical to the proper growth and maintenance of a natural in-situ microbial population. This allows for enhanced aerobic bioremediation of contaminated groundwater.
Copyright 2024. All Rights Reserved Solinst Canada Ltd.