Air sparging

Air sparging, also known as in situ air stripping[1] and in situ volatilization is an in situ remediation technique, used for the treatment of saturated soils and groundwater contaminated by volatile organic compounds (VOCs) like petroleum hydrocarbons[2] which is a widespread problem for the ground water and soil health.[3][4][5][6][7][8] The vapor extraction has manifested itself into becoming very successful and practical when it comes to disposing of VOCs.[9] It was used as a new development when it came to saturated zone remediation when using air sparging. Being that the act of it was to inject a hydrocarbon-free gaseous medium into the ground where contamination was found.[9] When it comes to situ air sparging it became an intricate phase process that was proven to be successful in Europe since the 1980s. Currently, there have been further development into bettering the engineering design and process of air sparging.[9]

Mechanism

Air Sparging is a subsurface contaminant remediation technique that involves the injection of pressurized air into contaminated ground water[1][10][11] causing hydrocarbons to change state from dissolved to vapor state.[12] The air is then sent to the vacuum extraction systems to remove the contaminants.[13][14] The extracted air or "off vapors" are treated to remove any toxic contaminants.[15]

Methods and treatment

Soil vapor Extraction (SVE) involves the use of multiple air injection points and multiple soil vapor extraction points that can be installed in contaminated soils to extract vapor phase contaminants above the water table. Contamination must be at least 3 feet deep beneath the ground surface in order for the system to be effective. A blower is attached to wells, usually through a manifold, below the water table creating pressure. The pressurized air forms small bubbles that travel through the contamination in and above water column. The bubbles of air volatilize contaminants and carry them to the unsaturated soils above. Vacuum points are installed in the unsaturated soils above the saturated zone. The vacuum points extract the vapors through to a Soil Vapor Extraction system. In order for the vacuum to avoid pulling the air from the surface, the ground has to be covered with a tarp or other method of sealing out surface air. Surface air intrusion into the system reduces efficiency and can reduce the accuracy of system metrics. The tarp is used to stop vapors from breakthrough to the surface above.[16] Soil vapor Extraction

The air sparging system treats the off-gases (referred as contaminated vapors and extracted air). The vapor is treated with granulated activated carbon prior to release to the atmosphere.[16] For example, arsenic-contaminated groundwater were treated by air sparging and what the treatment does is remove arsenic at certain percentage using solution of iron and arsenic only at a molar ratio of 2. Treatment using air sparging is beneficial as groundwater contains high amounts of dissolved iron, which contains the theoretical capacity for the treatment.[17]

Applicability

Air sparging is generally applied for commercial usage. Air sparging contaminant groups are VOCs and fuels found in groundwater. Air sparging is usually applied to the lighter gasoline constituents such as benzene, ethylbenzene, toluene, and xylene. This method is typically not applied on the heavier gasoline products such as kerosene and diesel fuels.[18] The usage of air sparging is commonly applied when cleaning up contaminated water under buildings and obstacles to prevent the further contamination of that water source. The usage of air sparging and SVE is safe when properly conducted. This makes sure only clean air that meets a certain quality standard is released, therefore it does not pose a threat when the proper sample method is done to make sure that hazardous gases do not exit into the atmosphere.[19]

References
  1. "Air Sparging". CPEO.
  2. Johnson, R.L.; et al. (Nov 1993). "An Overview of In Situ Air Sparging". Groundwater Monitoring & Remediation. 13 (4): 127–135. doi:10.1111/j.1745-6592.1993.tb00456.x.
  3. Redddy, Krishna R.; A. Adams, Jeffrey. "Cleanup of Chemical Spills Using Air Sparging" (PDF). Archived from the original (PDF) on 2013-12-02.
  4. Di Julio, S. S.; Drucker, A. S. "Air-Sparging Remediation: A Study on Heterogeneity and Air Mobility Reduction" (PDF). Journal of Hazardous Substance Research. 3.
  5. "Technology Overview Report" (PDF). Ground-Water Remediation Technologies Analysis Center. Oct 1996.
  6. "Air Sparging". Water and Soil Bio-Remediation. Archived from the original on 2013-12-02. Retrieved 2013-11-25.
  7. Reddy, Krishna R.; Tekola, Luesgald (2004). "Remediation of DNAPL source zones in groundwater using air sparging" (PDF). Land Contamination & Reclamation. 12 (2): 67–83. doi:10.2462/09670513.641. Archived from the original (PDF) on 2016-03-04.
  8. Bass, David H; et al. (2000). "Performance of air sparging systems: a review of case studies". Journal of Hazardous Materials. 72 (2–3): 101–119. doi:10.1016/S0304-3894(99)00136-3.
  9. Marley, Michael C.; Hazebrouck, David J.; Walsh, Matthew T. (1992-05-01). "The Application of In Situ Air Sparging as an Innovative Soils and Ground Water Remediation Technology". Ground Water Monitoring & Remediation. 12 (2): 137–145. doi:10.1111/j.1745-6592.1992.tb00044.x. ISSN 1745-6592.
  10. "Air Sparging Equipment Applications". Enviro-Equipment, Inc, Environmental Equipment & Supplies: Rental, Sales, Service & Repair.
  11. Ji, Wei; et al. (Nov 1993). "Laboratory Study of Air Sparging: Air Flow Visualization". Groundwater Monitoring & Remediation. 13 (4): 115–126. doi:10.1111/j.1745-6592.1993.tb00455.x.
  12. "A Citizen's Guide to Soil Vapor Extraction and Air Sparging" (PDF). EPA, United States Environmental Protection Agency, Office of Solid Waste and Emergency Response. Sep 2012.
  13. Suthersan, Suthan S. (1999). "In Situ Air Sparging" (PDF). Remediation Engineering : Design Concepts.
  14. "Underground Storage Tanks". U.S. Environmental Protection Agency. 2013-12-19.
  15. None, United States Environmental Protection Agency (30 November 2017). "A Citizen's Guide to Soil Vapor Extraction and Air" (PDF). EPA. Retrieved 30 November 2017.
  16. "A Citizen's Guide to Soil Vapor Extraction and Air Sparging". Environmental Protection Agency. 2015-04-09.
  17. MacBean, Edward A.; Brunsting, Joseph H. (April 2014). "In situ treatment of arsenic-contaminated groundwater by air sparging". Journal of Contaminant Hydrology. 159: 20–35. doi:10.1016/j.jconhyd.2014.01.003. PMID 24561624.
  18. “Air Sparging.” Air Sparging, www.cpeo.org/techtree/ttdescript/airspa.htm.
  19. EPA,OSWER,OSRTI, US. "A Citizen's Guide to Soil Vapor Extraction and Air Sparging | US EPA". EPA United States. Environmental Protection Agency.

Further reading
  • Nyer, Evan K; Suthersan, Suthan S (Nov 1993). "Air Sparging: Savior of Ground Water Remediations or just Blowing Bubbles in the Bath Tub?". Groundwater Monitoring & Remediation. 13 (4): 87–91. doi:10.1111/j.1745-6592.1993.tb00453.x.
  • Ji, Wei; et al. (1993). "Laboratory study of air sparging: Air flow visualization". Groundwater Monitoring & Remediation. 13 (4): 115–126. doi:10.1111/j.1745-6592.1993.tb00455.x.
  • Marley, Michael C.; Hazebrouck, David J.; Walsh, Matthew T. (1992). "The application of in situ air sparging as an innovative soils and ground water remediation technology". Ground Water Monitoring & Remediation. 12 (2): 137–145. doi:10.1111/j.1745-6592.1992.tb00044.x.
  • Johnson, Richard L.; et al. (1993). "An overview of in situ air sparging". Ground Water Monitoring & Remediation. 13 (4): 127–135. doi:10.1111/j.1745-6592.1993.tb00456.x.
  • Cabassud, C.; et al. (2001). "Air sparging in ultrafiltration hollow fibers: relationship between flux enhancement, cake characteristics and hydrodynamic parameters". Journal of Membrane Science. 181 (1): 57–69. doi:10.1016/s0376-7388(00)00538-x.
  • Hinchee, Robert E., ed. Air sparging for site remediation. Vol. 2. CRC Press, 1994.
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