Air sparging

Last updated September 12, 2023

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] a widespread problem for the ground water and soil health.^[3]^[4]^[5]^[6]^[7]^[8] Vapor extraction has become a very successful and practical method of VOC remediation.^[9] In saturated zone remediation, air sparging refers to the injection a hydrocarbon-free gaseous medium into the ground where contamination has been 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 developments 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 (0.91 m) 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]

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]

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.^[17] 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.^[18]

Arsenic-contaminated groundwater can be treated by air sparging to remove a certain percentage of arsenic in a solution of iron and arsenic 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.^[19]

Related Research Articles

Environmental remediation deals with the removal of pollution or contaminants from environmental media such as soil, groundwater, sediment, or surface water. Remedial action is generally subject to an array of regulatory requirements, and may also be based on assessments of human health and ecological risks where no legislative standards exist, or where standards are advisory.

Bioremediation broadly refers to any process wherein a biological system, living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings. The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment. In comparison to conventional physicochemical treatment methods bioremediation may offer considerable advantages as it aims to be sustainable, eco-friendly, cheap, and scalable. Most bioremediation is inadvertent, involving native organisms. Research on bioremediation is heavily focused on stimulating the process by inoculation of a polluted site with organisms or supplying nutrients to promote the growth. In principle, bioremediation could be used to reduce the impact of byproducts created from anthropogenic activities, such as industrialization and agricultural processes. Bioremediation could prove less expensive and more sustainable than other remediation alternatives.

<span class="mw-page-title-main">Soil contamination</span> Pollution of land by human-made chemicals or other alteration

Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity, agricultural chemicals or improper disposal of waste. The most common chemicals involved are petroleum hydrocarbons, polynuclear aromatic hydrocarbons, solvents, pesticides, lead, and other heavy metals. Contamination is correlated with the degree of industrialization and intensity of chemical substance. The concern over soil contamination stems primarily from health risks, from direct contact with the contaminated soil, vapour from the contaminants, or from secondary contamination of water supplies within and underlying the soil. Mapping of contaminated soil sites and the resulting cleanups are time-consuming and expensive tasks, and require expertise in geology, hydrology, chemistry, computer modeling, and GIS in Environmental Contamination, as well as an appreciation of the history of industrial chemistry.

Soil vapor extraction (SVE) is a physical treatment process for in situ remediation of volatile contaminants in vadose zone (unsaturated) soils. SVE is based on mass transfer of contaminant from the solid (sorbed) and liquid phases into the gas phase, with subsequent collection of the gas phase contamination at extraction wells. Extracted contaminant mass in the gas phase is treated in aboveground systems. In essence, SVE is the vadose zone equivalent of the pump-and-treat technology for groundwater remediation. SVE is particularly amenable to contaminants with higher Henry’s Law constants, including various chlorinated solvents and hydrocarbons. SVE is a well-demonstrated, mature remediation technology and has been identified by the U.S. Environmental Protection Agency (EPA) as presumptive remedy.

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<span class="mw-page-title-main">Rhizofiltration</span>

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<span class="mw-page-title-main">1,2,3-Trichloropropane</span> Chemical compound

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References

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↑ Reddy, Krishna R.; Tekola, Luesgald (2004). "Remediation of DNAPL source zones in groundwater using air sparging" (PDF). Land Contamination & Reclamation. 12 (2): 67–83. Retrieved 22 March 2023– via University of Illinois at Chicago.
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↑ "Underground Storage Tanks". U.S. Environmental Protection Agency. 2013-12-19.
↑ 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.
1 2 "A Citizen's Guide to Soil Vapor Extraction and Air Sparging". Environmental Protection Agency. 2015-04-09.
↑ “Air Sparging.” Air Sparging, www.cpeo.org/techtree/ttdescript/airspa.htm.
↑ EPA,OSWER,OSRTI, US. "A Citizen's Guide to Soil Vapor Extraction and Air Sparging | US EPA". EPA United States. Environmental Protection Agency.
↑ 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. Bibcode:2014JCHyd.159...20B. doi:10.1016/j.jconhyd.2014.01.003. PMID 24561624.